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Item 1A. Risk Factors.

Certain risk factors can significantly impact our business, liquidity, capital resources, results of operations, financial condition, and debt ratings. These risk factors might affect, alter, or change actions in executing our long-term capital strategy. Examples include, without limitation, contributing capital to any or all of our ten property and casualty insurance subsidiaries ("Insurance Subsidiaries"), issuing additional debt and/or equity securities, repurchasing our existing debt and/or equity securities, or increasing or decreasing common stockholders' dividends. We operate in a continually changing business environment, and new risk factors emerge from time to time. Consequently, we can neither predict such new risk factors nor assess their potential future impact on our business, if any.

Risks Related to our Insurance Operations

We are subject to losses from catastrophic events.

Losses from natural and human-made catastrophes can negatively impact our financial results. Examples include hurricanes, tornadoes, windstorms, earthquakes, hail, severe convective storms, severe winter weather, derechos, floods, and fires, some related to climate change, and criminal and terrorist acts, including cyber-attacks, civil unrest, and explosions. The frequency and severity of these catastrophes are inherently unpredictable, and the frequency and severity of catastrophe losses have increased globally in recent years. In many cases, the increase in catastrophe losses relate to small- to- medium-sized events that primary insurers retain and do not cede to reinsurers. Although we use sophisticated catastrophe modeling techniques to manage our catastrophe exposure, catastrophe models provide estimates that may materially differ from actual exposure and loss experience. For example, catastrophe models did not fully estimate the potential for some recent catastrophe loss activity (such as Winter Storm Elliott freeze losses in December 2022) and the concurrent recent economic inflation on construction costs.

Our insurance operations primarily write risks in the Eastern, Midwestern, and Southwestern regions of the U.S. Our most significant natural and/or human-made catastrophe exposures are (i) hurricanes impacting the Eastern U.S., (ii) severe convective storms, including hailstorms and tornadoes, (iii) winter storms, (iv) earthquakes, and (v) terrorism events. Single storms could adversely impact our financial results, but it is also possible that we could experience more than one severe catastrophic event in any given calendar year. We track our severe weather and catastrophe losses using definitions and

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information we obtain from Insurance Services Office, Inc.'s ("ISO") Property Claim Services unit, an internationally recognized authority on insured property losses from catastrophes in the U.S., Puerto Rico, and the U.S. Virgin Islands.

Certain factors can impact our estimates of ultimate costs for natural and/or human-made catastrophes, including:

•Inability to access portions of the affected areas after a catastrophic event;

•Scarcity of necessary labor and materials that delay repairs and increase our loss costs;

•Regulatory uncertainties, including new or expanded interpretations of coverage;

•Residual market assessment-related increases in our catastrophe losses;

•Potential fraud and inflated repair costs, partly driven by (a) demand surge post-event and (b) opportunistic service providers;

•Higher loss expenses due to shortages of claims adjusters available to appraise damage;

•Late claims reporting;

•Escalation of business interruption costs due to infrastructure disruption; and

•Whether the U.S. Secretary of the Treasury certifies an event as a terrorist act under TRIPRA.

Natural catastrophes

Temperature changes can impact weather patterns and the frequency and/or severity of catastrophes, including hurricanes, severe convective storms, wildfires, and flooding — all of which could cause our catastrophe losses to increase relative to historical levels.

A significant component of climate change risk is that the frequency and severity of extreme weather events may evolve differently relative to historical levels – leading to greater model uncertainty.Climate change models project significant differences in global regional warming above pre-industrial levels, depending on future levels of climate mitigation and geographic location. These global regional differences, whether attributable to nature or human activities, include increases in (i) mean temperature in most land and ocean regions, (ii) hot extremes in most inhabited regions, (iii) heavy precipitation in several regions, and (iv) the probability of drought and precipitation deficits in some regions.

Human-made catastrophes

Cyber Attacks and Incidents

The risk of a wide-scale criminal or terrorist cyber-attack has become more significant and has drawn increased attention from IT and national security experts, U.S. policymakers, the U.S. military, and the insurance industry. There is general recognition that a wide-scale cyber-attack that simultaneously impacts multiple victims is more likely, and insurance industry systemic risk has increased. We have identified three primary sources of potential insured exposure to cyber losses: (i) cyber-specific policies designed to cover both first-party and third-party losses; (ii) affirmative cyber coverage grants included in other types of policies, such as commercial property or businessowners policies; and (iii) "silent cyber" exposures, otherwise known as non-affirmative cyber exposures, which describes cyber risk that is neither expressly covered nor excluded in insurance policies. This exposure may exist if courts, regardless of intent, interpret policy forms without specific related coverage exclusions to provide coverage for a cyber-related incident.

We provide cyber-specific policies to our commercial lines and personal lines customers through 100% reinsured solutions with highly-rated specialty cyber markets. These solutions allow us to meet our customers' needs for cyber insurance while mitigating our underwriting risk as we develop our expertise in the cyber insurance market.

Beyond our cyber-specific policies, our other insurance policies provide some first- and third-party cyber coverages:

•We offer limited first-party affirmative cyber coverage in our commercial property and businessowners' policy forms. We limited our "silent cyber" exposure through an affirmative coverage grant subject to a sub-limit.

•Our base property forms typically include a coverage grant of $2,000 or $10,000. Most of our property policies also contain an affirmative endorsement providing "virus and harmful code" coverage subject to a sub-limit. Over 90% of our policies with virus/harmful code coverage on commercial property, businessowners', commercial output policy, or inland marine forms have sub-limits of $25,000 or lower. For policies effective October 1, 2022 and later, we implemented cyber incident exclusions that exclude malicious cyber except for the sub-limited coverage provided in the base ISO coverage forms and our property and businessowners' property “virus and harmful code” extension endorsements. These exclusions clarify coverage and have no premium impact.

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•Most of our general liability and businessowners' policies exclude cyber-related liability losses, except for "bodily injury." Our specific cyber-exclusion and liability forms' lack of affirmative sub-limited cyber coverage, effectively limit most "silent cyber" exposure.

•By statute, workers compensation policies do not have cyber exclusions, and a cyber-attack-related workplace injury could trigger coverage.

Terrorism

We are required to participate in TRIPRA, now extended to December 31, 2027, for our Standard Commercial Lines and E&S Lines business. TRIPRA rescinded all previously approved coverage exclusions for terrorism and requires private insurers and the U.S. government to share the risk of loss on future acts of terrorism certified by the U.S. Secretary of the Treasury. Under TRIPRA, each participating insurer must pay a significant deductible of specified losses before federal assistance is available. Our $543 million deductible is based on a percentage of our prior year’s applicable Standard Commercial Lines and E&S Lines premiums. In 2024, the federal government will pay 80% of losses above the deductible, with the insurer retaining 20%. Although TRIPRA will mitigate some of our loss exposure to a large-scale terrorist attack, our deductible could have a material adverse effect on our results of operations, liquidity, financial condition, financial strength, and debt ratings. If the U.S. Secretary of the Treasury does not certify specific terrorist events, we could be required to pay terrorism-related covered losses without TRIPRA's risk-sharing benefits. We also could be required to pay terrorism-related losses for customers who declined terrorism coverage.

Our primary workers compensation policies are required to cover terrorism risk, so TRIPRA applies to those policies. Insureds with non-workers compensation commercial policies can accept or decline our terrorism coverage or negotiate with us for other terms. In 2023, 85% of our Standard Commercial Lines non-workers compensation policyholders purchased terrorism coverage that included nuclear, biological, chemical, and radioactive ("NBCR") events. TRIPRA also applies to cyber liability insurance policies reported under a Terrorism Risk Insurance Program-eligible line of insurance.

Many states mandate that commercial property policies cover fire following an act of terrorism - regardless of whether the insured purchased terrorism coverage. We also sometimes elect to provide terrorism coverage for lines of business not included in TRIPRA, such as Commercial Automobile. TRIPRA has never covered personal lines of business. Our Standard Personal Lines homeowner policies exclude nuclear losses but not biological, chemical, or conventional terrorism losses. Our current reinsurance programs cover some losses from conventional foreign and domestic terrorism acts but not NBCR events.

An increase in natural or man-made catastrophe losses, including a systemic cyber-attack that produces an aggregation of property and/or casualty cyber losses, will reduce our net income and stockholders’ equity and could have a material adverse effect on our liquidity, financial strength, and debt ratings. The closer a catastrophe occurs to the end of a reporting period, the more likely we have limited information to estimate loss and loss expense reserves, increasing the uncertainty of our estimates. More comprehensive claims information available after a reporting period may result in reserve changes in subsequent periods.

Our loss and loss expense reserves may not adequately cover actual losses and expenses.

We maintain reserves for our estimated liability for loss and loss expense associated with reported and unreported insurance claims. Estimating loss and loss expense reserves is inherently uncertain, and there is no method for precisely estimating the ultimate liability for the settlement of claims. We base our loss and loss expense reserve estimates on our internal in-depth reserve review, which uses our loss experience, claims payment and reporting patterns, and our view of underlying claims frequency and severity trends. We supplement the estimates with other subjective considerations, including projected impacts from economic, political, social, and legal developments or trends, such as inflation, continually evolving trends driven by the post-COVID-19 pandemic environment, judicial trends and tort decisions, and various state legislative initiatives. We cannot predict the timing or impact of these developments or trends with certainty, and we cannot be sure the reserves we establish are adequate or will be so in the future.

We review our reserve position quarterly and adjust the reserve position accordingly. An increase in reserves (i) reduces net income and stockholders' equity, and (ii) could have a material adverse effect on our liquidity, financial strength, and debt ratings. As we underwrite new business and renew existing business, we estimate future loss cost trends in pricing our products to generate an adequate risk-adjusted return. If our future loss cost trend estimates prove to be understated, our pricing of future new and renewal business could be inadequate to cover actual loss costs, and our future loss and loss expense reserves could be understated.

Three examples of how loss and loss expense reserves might be affected by economic, political, social, or legal developments or trends are:

•If economic inflation, including medical inflation, is higher than our assumptions, our loss and loss expense reserves

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for our longer tail lines of business could be insufficient. For example, 2022 inflation rates reflected in the overall consumer price index ("CPI"), the Core CPI, and the Producer Price Index, were higher than 2021. While inflation moderated in 2023, it remains elevated relative to the Federal Reserve’s long-term 2% target. The workers compensation line of business is particularly susceptible to inflation because of its extended payment pattern and exposure to medical care services and commodities. While medical inflation has been benign for several years, these medical care costs could have a more material impact on our overall loss and loss expense reserves if they were to rise significantly or persist at a higher level for an extended period. Our short-tail property lines of business are also susceptible to inflation because of their exposure to increased labor and material costs.

•Social inflation refers to the phenomenon where societal factors, such as attitudes, perceptions, and cultural changes, contribute to increased insurance claims costs and litigation. It often leads to higher payouts in legal settlements and impacts insurance premiums for businesses and individuals. This inflation is driven by various factors, including changing jury attitudes, increased litigation funding, and larger awards in court cases. Social inflation can affect all lines of business, but the automobile liability, general liability, and corresponding umbrella lines of business that involve third-party claimants tend to be more susceptible to social inflationary impacts. Our reserve for loss and loss expense could be insufficient if the social inflation impacts exceed our assumptions.

•Various states have expanded or could expand the statute of limitations for civil actions alleging sexual abuse. By retroactively permitting previously time-barred claims, these "reviver" laws may result in insurance claims that could significantly increase loss costs and require re-evaluating previously-established reserves or creating new reserves. Since reviver statutes have been enacted, we have received some notices of claims or potential claims for acts alleged to have occurred, some dating as far back as the 1950s. Without prior experience, we cannot estimate how many "reviver" claims notices we may receive. Most notices (i) are blanket notices sent by attorneys representing claimants unsure of the alleged assailant or supervising entity's insurer or policy (if any) and (ii) may not implicate any of our or a predecessor's insurance policies. For those we determine implicate one of our or a predecessor's policy, we (i) have investigated or are investigating facts, (ii) have evaluated policy terms, (iii) believe we have appropriate coverage defenses to most of these claims and/or sufficient reinsurance protections, and (iv) have considered these factors in establishing our reserves, which we believe provide a reasonable estimate of the aggregate ultimate net exposure for these claims. Our coverage positions may be challenged through litigation or otherwise, so we face litigation risks. These are discussed further below in the Risk Factor entitled, "We are engaged in ordinary routine legal proceedings incidental to our insurance operations that are inherently unpredictable and could impact our reputation and/or have a material adverse effect on our consolidated results of operations or cash flows in particular quarterly or annual periods."

For further discussion on our loss and loss expense reserves, please see the "Critical Accounting Policies and Estimates" section of Item 7. "Management’s Discussion and Analysis of Financial Condition and Results of Operations." and Note 2. "Summary of Significant Accounting Policies" in Item 8. "Financial Statements and Supplementary Data." of this Form 10-K.

Our ability to reduce our risk exposure depends on the availability and cost of reinsurance.

We transfer a significant portion of our underwriting risk to third parties through reinsurance contracts. These contracts provide reimbursement of losses exceeding specified amounts or percentages of premiums. Typically, our reinsurance coverages align with the coverages offered under our primary insurance policies.

The availability, quality, amount, and cost of reinsurance depend on market conditions, including traditional privately placed reinsurance, retrocessional reinsurance, and catastrophe bond market capacity. Most of our reinsurance contracts have annual terms. Consequently, reinsurance costs may fluctuate significantly, not necessarily correlating to the loss experience of our specific book of business. State insurance regulators generally permit us to consider catastrophe reinsurance expense in our filed rates and rating plans. However, the conditions and timing of regulatory approval may not align with the actual expense of new reinsurance terms. Disproportionate increases in our reinsurance expense that we cannot include in our filed rates and rating plans will reduce our earnings. If we cannot negotiate desired reinsurance amounts or terms, we may experience increased reinsurance expense and increased risk retention on individual or aggregate claim losses that could limit our ability to write future business.

Commercial property and homeowners coverages have historically accounted for most of our catastrophe-related claims. To limit our exposure to catastrophe losses, we purchase catastrophe reinsurance. Our reinsurance coverage may prove to be inadequate, particularly if:

•We do not purchase sufficient amounts of reinsurance because of defects or inaccuracies in the various modeling

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software programs we use to analyze our Insurance Subsidiaries' risk;

•A major catastrophe loss exceeds (i) the purchased reinsurance limit or (ii) the financial capacity of one or more of our reinsurers even if the loss is within the purchased limit;

•The combination of multiple catastrophe events in a single year is such that our Insurance Subsidiaries' insured losses exceed the aggregate limits of the catastrophe reinsurance treaty or our Insurance Subsidiaries experience an unusually large number of catastrophe losses that fall below our per occurrence reinsurance retention;

•Our reinsurance counterparties (i) are unable to access their reinsurance markets, or retrocessions, (ii) suffer significant financial losses, (iii) are sold, (iv) cease writing reinsurance business, or (v) are unable or unwilling to satisfy their contractual obligations to us; or

•The catastrophe losses insured in our primary policies are excluded from coverage in our reinsurance contracts.

Recent economic, geopolitical, and insured loss events have increased global reinsurance market uncertainty. Reinsurance prices have increased, and the availability of reinsurance has reduced due to the impacts of (i) social inflation on liability claim outcomes, including exceptionally high jury awards, (ii) reduced capacity due to reinsurer investment portfolio losses, (iii) weakened Euro-United States dollar currency exchange rates, (iv) challenged reinsurer profitability in recent years, and (v) investor and reinsurer concerns about the potential impacts of climate change. While reinsurance market conditions stabilized somewhat in 2023, purchasers of reinsurance continue to face higher pricing, less reinsurance availability and more market uncertainty than they did pre-2022. We face increased underwriting risk for exposure to specific primary policy losses from risks, like cyber and communicable diseases, now principally excluded from coverage under our reinsurance treaties. Our reinsurance contracts also contain coverage terms restricting our ability to cede certain types of potential losses related to terrorism. Increased underwriting risk could increase our net loss and loss expense, increasing our underwriting results volatility. Decreased reinsurance capacity would also increase our underwriting risk if we cannot fully place our target reinsurance treaty coverage on renewal. If our reinsurers have difficulty collecting their retrocession programs or reinstating retrocession coverage after a large loss, our reinsurance claims may not be timely or fully paid.

Even with the benefits of reinsurance, our catastrophe risk exposure could have a material adverse effect on our results of operations, liquidity, financial condition, financial strength, and debt ratings.

We are exposed to credit risk.

We face credit risk in several areas of our insurance operations, including from:

•Our reinsurers, which are obligated to make us payments under our reinsurance agreements. Reinsurance credit risk can fluctuate over time, increasing during periods of high industry catastrophe and liability losses. Reinsurers generally manage their significant loss exposure through their own reinsurance programs, or retrocessions, and we do not always have the full details about them. If our reinsurers experience difficulty collecting on their retrocession programs or reinstating retrocession coverage after a large loss, we may not receive timely or full payment of our reinsurance claims. This means that we have direct and indirect counterparty credit risk to our reinsurers and the reinsurance industry, which is a global but concentrated market.

•Certain life insurance companies, if they fail to fulfill their contractual obligations to our policyholders or claimants under annuities we purchased as part of structured claims settlements.

•Some of our independent distribution partners, who collect premiums from policyholders for us.

•Some policyholders, who are directly obligated to us for premium and/or deductible payments, the timing of which may be impacted by mandated payment moratoriums.

Our exposure to credit risk could have a material adverse effect on our results of operations, liquidity, financial condition, financial strength, and debt ratings.

We depend on distribution partners.

We market and sell our insurance products through independent, non-employee distribution partners. Independent distribution partners have – and we expect will continue to have – a significant role in overall insurance industry premium production. While our customers find advantages in using independent distribution partners, our reliance on independent distribution partners presents risks and challenges, including:

•Competition in our distribution channel, as we must market our products and services to independent distribution partners who have access to products from multiple carriers and markets.

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•Brand recognition challenges because we closely coordinate marketing with our distribution partners and some customers do not differentiate their insurance agent from their insurer.

•Our market share growth is tied to our distribution partners' market share. Consequently, growth in our Standard Personal Lines could be more limited than in our Standard Commercial Lines. Competitors have focused on lower-cost "direct-to-customer" distribution models emphasizing digital ease and efficiencies to address the discrepancy in agency control of standard personal lines business. Continued advancements in "direct-to-customer" distribution models may impact our independent distribution partners' overall market share, make it more difficult for us to grow, or require us to establish relationships with more distribution partners.

•Aggregation and consolidation of our independent distribution partners and their market share. Some publicly traded and private equity-backed independent distribution partners have deployed consolidation strategies to acquire other independent distribution partners and increase their market share ("Aggregators") over the last decade. If more of our independent distribution partners become Aggregators or Aggregators acquire them, Aggregator demands and influence on our business could increase. For example, Aggregators could develop and implement strategies to consolidate their business with fewer insurers and demand higher base and supplemental commissions. Aggregators accounted for approximately 43% of our DPW at December 31, 2023, up from 33% three years ago. No one distribution partner is responsible for 10% or more of our combined insurance operations' premium.

Our financial condition and results of operations are impacted by our independent distribution partners' success in marketing and selling our products and services.

National and global economic conditions could adversely and materially affect our business, results of operations, financial condition, and growth.

Unfavorable economic developments, such as increased inflation levels, could adversely affect our earnings if our policyholders need less insurance coverage, cancel existing insurance policies, modify coverage, or choose not to renew with us. Inflation could significantly impact our claims severity across multiple lines of business and could result in adverse reserve development. An economic downturn could also lead to increased credit and premium receivable risk, failure of reinsurance counterparties and other financial institutions, limitations on our ability to issue new debt, reduced liquidity, and declines in our investments' fair value and financial strength ratings. These potential events and other economic factors could adversely and materially affect our business, results of operations, financial condition, and growth. During 2023, 26% of DPW in our Standard Commercial Lines business was based on payroll or sales of our underlying policyholders. An economic downturn in which our policyholders have declining revenue or employee count could adversely affect our total written premium, including audit and endorsement premium.

We write business domestically in the United States, and our insurance operations do not have direct exposure to businesses or individuals in Russia, Ukraine, Israel, or the West Bank. We do not have material exposure to investments subject to embargoes or Russian reinsurance counterparties. However, ongoing wars and conflicts are impacting global economic, banking, commodity, and financial markets by exacerbating ongoing economic challenges, including inflation and supply chain disruption, which influence insurance loss costs, premiums, and investment valuation. The Israeli-Hamas war is creating global political tension that could result in some countries taking political or economic actions, such as Iran's support for the Houthi rebels in Yemen, that could impact the U.S. and global economies.

A downgrade or a potential downgrade in our financial strength or credit ratings could result in a loss of business and have a material adverse effect on our financial condition and results of operations.

A significant financial strength rating downgrade, particularly from AM Best Company ("AM Best"), would affect our ability to write new or renewal business. Most policyholders are required by various third-party agreements, primarily with lenders, to maintain insurance policies from a carrier with a minimum rating from AM Best or Standard & Poor's Global Ratings. Credit rating downgrades could also make it more expensive to access capital markets. We cannot predict rating actions issued by nationally recognized statistical rating organizations that might adversely affect our business or our potential responses. Any significant downgrade in our financial strength and credit ratings below an "A-" could have a material adverse effect on our results of operations, liquidity, financial condition, financial strength, and debt ratings. For additional information on our current financial strength and credit ratings, refer to "Overview" in Item 1. "Business." of this Form 10-K.

Markets for insurance products and services are highly competitive and subject to rapid technological change, and we may be unable to compete effectively.

We offer our insurance products and services in a highly competitive market characterized by (i) consumer and business price sensitivity, (ii) aggressive price competition, and (iii) improvements based on performance characteristics and large data sets. These factors can compact underwriting margins, new products and services, evolving industry standards, and rapid adoption of

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technological advancements. Our ability to compete depends heavily on our timely and consistent introduction of innovative new products and services.

We face substantial competition from a wide range of property and casualty insurance companies for customers, distribution partners, and employees. Competitors include public, private, and mutual insurance companies. Many competitors are larger and may have lower relative operating costs, lower capital costs, or greater capacity to absorb or diversify more risk while maintaining their financial strength ratings. Other competitors, such as mutual or reciprocal companies, are owned by or operated cooperatively for insureds and, unlike us, do not have shareholders who evaluate ROE performance. Consequently, some competitors may be able to price their products more competitively.

The Internet has emerged as a significant competitive digital marketplace for existing and new competitors. Established insurance competitors are beginning to explore broader digital Internet offerings and implement artificial intelligence ("AI"). New competitors with variations on traditional business models have emerged. Because the Internet makes it easier and less expensive to bundle products and services, it is also possible that non-insurance companies conducting business on the Internet could enter the insurance business or form strategic alliances with insurers. Changes in competitors and competition, particularly on the Internet, could cause changes in the supply or demand for insurance and adversely affect our business.

The increasing importance of the Internet, technology, AI, and digital strategies in our industry also demands that we attract and retain employees in difficult-to-fill data science, advanced analytics, and information technology ("IT") roles. If we cannot attract and retain such employees, our results of operations and financial condition could be materially and adversely affected.

We have less loss experience data than our larger competitors.

Insurers depend on access to reliable data about their policyholders and loss experience to build complex analytics and predictive models that assess risk profitability, reserve adequacy, adverse claim development potential, recovery opportunities, fraudulent activities, and customer buying habits. Because we use and depend on the aggregated industry loss data assembled by rating bureaus under the antitrust exemptions of the McCarran-Ferguson Act, we likely would be at a competitive disadvantage to larger insurers if Congress repealed the McCarran-Ferguson Act.

We expect the importance of data science and analytics to increase, becoming more complex and accurate with larger sets of relevant data. Some larger competitors have significantly more data about the performance of their underwritten risks. In comparison, we may not have sufficient volumes of loss experience data to analyze and project our future costs as accurately or granularly. We supplement our data with industry loss experience from Verisk, American Association of Insurance Services, Inc., the National Council on Compensation Insurance, Inc., and other publicly available sources. While relevant, industry data may not correlate specifically to the performance of our underwritten risks or be as predictive as data on a larger book of our own business.

We are subject to various modeling risks that could have a material adverse impact on our business results.

We rely on complex financial and other statistical models, developed internally and by third parties, to predict (i) underwriting results on individual risks and our overall portfolio, (ii) claims fraud and other claims impacts, such as escalation, (iii) impacts from catastrophes, (iv) enterprise risk management capital scenarios, and (v) investment portfolio changes. We rely on these financial and other statistical models to analyze historical loss costs and pricing, claims severity and frequency trends, catastrophe losses, reinsurance attachment and exhaustion points, investment performance, portfolio risk, and our economic capital position. Flaws or limitations in financial and statistical models and their embedded assumptions could increase losses. For example, a significant component of climate change risk is that the frequency and severity of extreme weather events may evolve differently relative to historical levels – leading to greater model uncertainty. In addition, increasing insurance regulatory interest in data and model use, combined with any potential restrictions on traditional rating factors or model use, could have a material adverse impact on our financial condition and operating results. Our statistical models are extremely useful in monitoring and controlling risk, but are no substitute for senior management's experience or judgment.

Risks Related to Our Investments Segment

Our investments are exposed to credit risk, interest rate fluctuation, and changes in value.

We depend on income from our investment portfolio for a significant portion of our revenue and earnings. Our investments can be negatively affected by (i) liquidity, (ii) credit deterioration, (iii) financial results, (iv) public equity and/or debt market changes, (v) economic conditions, including heightened levels of economic inflation, (vi) political risk, (vii) sovereign risk, (viii) interest rate fluctuations, or (ix) other factors, including climate change risk and civil unrest.

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Our investment portfolio's value is subject to credit risk from our held securities' issuers, guarantors, and financial guarantee insurers, and other counterparties in certain transactions. Defaults on any of our investments by any issuer, guarantor, financial guarantee insurer, or other counterparty could reduce our net investment income and increase net realized investment losses. We are subject to the risk that the issuers or guarantors of our fixed income securities may default on principal and interest payment obligations.

Additionally, we are exposed to interest rate risk, primarily related to the market price and cash flow variability associated with changes in interest rates. Consequently, the amount of our cash and cash equivalents and the value and liquidity of our marketable and non-marketable securities may fluctuate substantially. Future fluctuations in the value of our cash, cash equivalents, and marketable and non-marketable securities could result in significant losses that have a material adverse impact on our financial condition and operating results.

Our investment portfolio is exposed to climate change-related transition and physical investment risks.

•Transition risks arise from society’s transition to a low-carbon economy, driven by policy and regulations, low-carbon technology advances, and shifting public sentiment and societal preferences. This transition to renewable energy sources may lead to (i) stranded assets in sectors with high carbon footprints or those closely tied to carbon-based economic activity, such as the fossil fuel and automotive industries, (ii) increased costs for infrastructure reinvestment and replacement, and litigation defense of carbon-intensive sectors, (iii) lower corporate profitability, (iv) lower property values, and (v) lower household wealth. The Paris Agreement Capital Transition Assessment defines the carbon-intensive sectors as the most exposed to transition risks: oil and gas, coal, power, automotive, cement, aviation, and steel. As of December 31, 2023 and December 31, 2022, carbon-intensive sectors within our fixed income securities portfolio represented about 4% of our total invested assets.

•Physical investment risks include the risk of investment losses on our commercial and residential mortgage-backed securities exposed to climate-related catastrophic losses that can cause business disruption, destroy capital, increase costs to recover from disasters, reduce revenue, and cause population displacement and migration. These, in turn, can lower residential and commercial property values, household wealth, and corporate profitability, potentially creating financial and credit market losses impacting insurer asset values. As of December 31, 2023, about 70% of our residential mortgage-backed securities were backed by government agencies. We generally invest in the top tranches of commercial mortgage-backed securities, which limit potential losses from property value declines. As of December 31, 2023, about 75% of our commercial mortgage-backed securities had "AAA" credit ratings.

Significant future investment value declines could require further losses recorded on securities we sell and credit losses. For more information regarding market interest rate, credit, and equity price risk, see Item 7A. "Quantitative and Qualitative Disclosures About Market Risk." of this Form 10-K.

We are subject to the risks inherent in investing in private limited partnerships.

Our alternative investments include private limited partnerships that invest in various strategies, such as private equity, private credit, and real assets. The primary assets and liabilities underlying these limited partnership investments generally do not have quoted prices in active markets for the same or similar assets. Consequently, their valuation is subject to a higher level of subjectivity and unobservable inputs than most of our other investments. We record these limited partnership investments under the equity method of accounting, so valuation decreases could negatively impact our results of operations.

Determining the amount of credit losses taken on our investments is highly subjective and could materially impact our results of operations or our financial position.

The determination of the amount of credit losses taken on our investments is based on our quarterly evaluation and assessment of our investments and known and inherent risks associated with the various asset classes. Our allowance for credit losses is subject to significant judgments and assumptions regarding changes in economic conditions, estimated future cash flows, and the accuracy of third-party information used in internal assessments. We revise our evaluations and assessments as conditions change and new information becomes available. There can be no assurance that management has accurately assessed the level of credit losses recorded in our Financial Statements. For further information about our evaluation and considerations for determining whether a security has a credit loss, please refer to "Critical Accounting Policies and Estimates" in Item 7. "Management’s Discussion and Analysis of Financial Condition and Results of Operations." of this Form 10-K.

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Risks Related to Evolving Laws, Regulations, and Public Policy Debates

We are subject to complex and changing laws, regulations, and public policy debates that expose us to regulatory scrutiny, potential liabilities, increased costs, reputational harm, and other adverse effects on our business.

Our operations are subject to complex and changing state and federal laws, regulations, and public policy debates on subjects, including, without limitation, the following:

•Pricing and underwriting practices;

•Claims practices;

•Loss and loss expense reserves;

•Exiting geographic markets and/or canceling or non-renewing policies;

•Sustainability-related issues, including sustainability investment mandates;

•Climate change, including potential liability for related public disclosures;

•Assessments for guaranty funds and second-injury funds, and other mandatory assigned risks and reinsurance;

•The types, quality, and concentration of investments we make;

•Minimum capital requirements for the Insurance Subsidiaries;

•Dividends from our Insurance Subsidiaries to the Parent;

•Privacy and data security;

•Tax;

•Antitrust;

•Consumer protection;

•Advertising;

•Sales;

•Billing and e-commerce;

•Intellectual property ownership and infringement;

•Digital platforms;

•Internet, telecommunications, and mobile communications;

•Media and digital content;

•Availability of third-party software applications and services;

•Labor and employment;

•Anti-money laundering; and

•Workplace environmental, health, and safety issues.

Changes to laws and regulations can adversely affect our business by increasing our costs, limiting our ability to offer a product or service to customers, requiring changes to our business practices, or otherwise making our products and services less attractive.

While we underwrite risks only in the U.S., international regulatory developments, primarily capital adequacy and risk management requirements in the European Union ("EU"), may influence U.S. regulators as they develop or revise domestic regulatory standards.

We have implemented policies and procedures designed to ensure compliance with applicable laws and regulations. However, we can provide no assurance that our employees, contractors, or independent distribution partners will not violate such laws and regulations or our policies and procedures. To some degree, we have multiple regulators whose authority may overlap and may have different interpretations and/or regulations related to the same legal issues. Consequently, we have the risk that one regulator's position or interpretation may conflict with another regulator on the same point. For example, if Congress passed legislation regulating insurer solvency oversight and state regulators remained responsible for rate approval, we could be subject to a conflicting regulatory framework that could impact our profitability and capital adequacy. The cost of complying with various laws and regulations, potentially conflicting laws and regulations, and changes in those laws and regulations, could have a material adverse effect on our results of operations, liquidity, financial condition, financial strength, and debt ratings.

Insurers are subject to regulatory, political, and media scrutiny. We are subject to government market conduct reviews and investigations, legal actions, and penalties. There can be no assurance that our business will not be materially adversely affected by the outcomes of such examinations, investigations, or media scrutiny in the future. If we are found to have violated laws and regulations, it could materially adversely affect our reputation, financial condition, and operating results.

Our business is subject to various state, federal, and other laws, rules, policies, and other obligations regarding data use and protection.

We are subject to federal and state laws relating to collecting, using, retaining, securing, and transferring personally identifiable

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information ("PII"). Federal laws include the Gramm-Leach-Bliley Act, the Fair Credit Reporting Act, the Drivers Privacy Protection Act, the Health Insurance Portability and Accountability Act, and Unfair and Deceptive Acts and Practices laws. Several states, like New York, Nevada, Colorado, Virginia, and California, have passed laws in this area, and other jurisdictions are considering imposing additional restrictions or creating new rights concerning PII. These laws continue to develop and may be inconsistent from jurisdiction to jurisdiction. Complying with emerging and changing requirements may cause us to incur substantial costs or require us to change our business practices. Noncompliance could result in significant reputational harm, penalties, and legal liability.

The EU adopted the General Data Protection Regulation ("GDPR") in 2016, but it was not effective until 2018. GDPR regulates data protection and privacy in the EU and transfers of personal data outside the EU. GDPR’s main tenet is to give individuals primary control over their personal data. Because we do not write coverages in the EU, GDPR does not directly impact us. Some U.S. states have subsequently incorporated individual-control mechanisms into state privacy laws. Future EU data privacy actions likely will influence U.S. regulators over time.

We make statements about our use and disclosure of PII in our privacy policy on our website, and in other public venues. We could be subject to litigation or governmental actions if we fail to comply with these public statements or federal and state privacy-related and data protection laws and regulations. Such proceedings could impact our reputation and result in penalties, including ongoing audit requirements and significant legal liability.

We are engaged in ordinary routine legal proceedings incidental to our insurance operations that are inherently unpredictable and could impact our reputation and/or have a material adverse effect on our consolidated results of operations or cash flows in particular quarterly or annual periods.

We are engaged in ordinary routine legal proceedings incidental to our insurance operations that include:

•Defense of or indemnity for third-party suits brought against our insureds;

•Defense of actions brought against us by our insureds who disagree with our coverage decisions, some of which allege bad faith claims handling and seek extra-contractual damages, punitive damages, or other penalties;

•Actions we file, primarily for declaratory judgment, seeking confirmation that we have made appropriate coverage decisions under our insurance contracts;

•Actions brought against competitors or us alleging improper business practices and sometimes seeking class status. Such actions historically have included issues and allegations, without limitation, related to (i) unfairly discriminatory underwriting practices, including the impact of credit score usage, (ii) managed care practices, such as provider reimbursement, and (iii) automobile claims practices; and

•Actions we file against third parties and other insurers for subrogation and recovery of other amounts we paid on behalf of our insureds.

From time to time, legal proceedings in which we are involved may receive media attention based on their perceived newsworthiness and/or relationship to various broad economic, political, social, and legal developments or trends. Such media stories could negatively impact our reputation.

We expect any potential ultimate liability for ordinary routine legal proceedings incidental to our insurance business will not be material to our consolidated financial condition after considering estimated loss provisions. Litigation outcomes, however, are inherently unpredictable, even with meritorious defenses. The time a case is in litigation also is unpredictable, as state court dockets are increasingly overcrowded. Generally, the longer a case is in litigation, the more expensive it can become. Because the amounts sought in certain actions are large or indeterminate, any adverse outcomes could have a material adverse effect on our consolidated results of operations or cash flows in particular quarterly or annual periods.

Additionally, we do not have any material litigation risks related to climate change.

Risks Related to Our Corporate Structure and Governance

We are a holding company, and our ability to declare dividends to our shareholders, pay indebtedness, and enter into affiliate transactions may be limited because our Insurance Subsidiaries are regulated.

Restrictions on our Insurance Subsidiaries' ability to pay dividends, make loans or advances to the Parent, or enter into transactions with affiliates may materially affect our ability to pay dividends on our preferred and common stock or repay our indebtedness. Based on these restrictions, there is a maximum ordinary annual dividend amount the Insurance Subsidiaries can provide the Parent. Our Insurance Subsidiaries' ability to pay dividends or make loans or advances is subject to the approval or review of our domiciliary state insurance regulators. For additional details regarding dividend restrictions, see Note 22.

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"Statutory Financial Information, Capital Requirements, and Restrictions on Dividends and Transfers of Funds" in Item 8. "Financial Statements and Supplementary Data." of this Form 10-K.

The Parent’s ability to pay dividends to its stockholders is also impacted by covenants in its credit agreement (the "Line of Credit") among the Parent, the named lenders (the "Lenders"), and Wells Fargo Bank, National Association, as Administrative Agent. These covenants obligate the Parent to, among other things, maintain a minimum consolidated net worth and a maximum ratio of debt to capitalization. Our preferred stock's terms limit the Parent's ability to declare or pay dividends on, or purchase, redeem, or otherwise acquire shares of its common stock or any shares of the Parent that rank junior to, or on parity with, the preferred stock if the Parent does not declare and pay (or set aside) dividends on the preferred stock for the last preceding dividend period. For additional details about the Line of Credit's financial covenants, see Note 11. "Indebtedness" in Item 8. "Financial Statements and Supplementary Data" of this Form 10-K. For additional details about conditions related to our preferred stock, see Note 17. "Equity" in Item 8. "Financial Statements and Supplementary Data" of this Form 10-K.

Because we are a New Jersey corporation and an insurance holding company, we may be less attractive to potential acquirers and our common stock's value could be adversely affected.

We are a New Jersey company, and provisions of the New Jersey Shareholders' Protection Act and our Amended and Restated Certificate of Incorporation may discourage, delay, or prevent us from being acquired. A supermajority of our shareholders must approve (i) certain business combinations with interested shareholders or (ii) any amendment to the related provisions of our Amended and Restated Certificate of Incorporation unless certain conditions are met. These conditions may relate to, among other things, the interested stockholder's acquisition of stock, the approval of the business combination by disinterested members of our Board and disinterested stockholders, and the price and payment of the consideration proposed in the business combination. In addition to considering the effects of any action on our shareholders (including any offer or proposal to acquire the Parent), our Board may consider (i) the long-term, and short-term interests of the Parent and our shareholders, including the possibility that the Parent’s continued independence may best serve these interests, (ii) the effects of the action on the Parent's employees, suppliers, creditors, and customers, and (iii) the effects of the action on the community in which the Parent operates.

These provisions of our Amended and Restated Certificate of Incorporation and New Jersey law could deprive our common shareholders of an opportunity to receive a premium over the prevailing market price in a hostile takeover and could adversely affect the value of our common stock.

Because we own insurance subsidiaries, any party seeking to acquire 10% or more of our common stock must seek prior approval from the subsidiaries' domiciliary insurance regulators and file extensive information about their business operations and finances. The New Jersey Department of Banking and Insurance Commissioner, who regulates seven of our Insurance Subsidiaries, also considers whether (i) the acquisition of control of an insurer would be adverse to the public interest or the protection of existing and future policyholders or (ii) persons seeking control would use control adversely to the public interest or the protection of policyholders.

Risks Related to Our General Operations

We and our distribution partners and vendors are subject to attempted cyber-attacks and other cybersecurity and system availability risks.

Our business heavily relies on IT and application systems connected to or accessed from the Internet. Consequently, a malicious cyber-attack could affect us. Our systems also house proprietary and confidential information about our operations, employees, agents, and customers and their employees and property, including PII. A malicious cyber-attack on (i) our systems, (ii) our distribution partners or their key operating systems, and (iii) any other of our third-party partners or vendors and their key operating systems may interrupt our ability to operate, damage our reputation and result in monetary damages that are difficult to quantify, and have a material adverse effect on our results of operations, liquidity, financial condition, financial strength, and debt ratings.

Through encryption and authentication technologies, we have implemented systems and processes intended to mitigate or secure our IT systems and prevent unauthorized access to, or loss of, sensitive data. Cyber-attacks continue to evolve daily, so our security measures may not be sufficient for all eventualities. We may be vulnerable to hacking, employee error, malfeasance, system error, faulty password management, or other irregularities. These risks may be higher or lower for our third-party providers depending on the maturity of their security program, and we review their control environments to the extent possible and practical, aligning the risk exposure with our business requirements and risk tolerances. Any disruption or breach of our systems or data security could damage our reputation, result in monetary damages that are difficult to estimate, and have a material adverse effect on our results of operations, liquidity, financial condition, financial strength, and debt ratings. To mitigate this risk, we have and expect to continue to (i) conduct employee education programs and tabletop exercises and (ii) develop and invest in a variety of controls to prevent, detect, and appropriately react to cyber-attacks, including frequently

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testing our systems' security and access controls. We have insurance coverage for certain cybersecurity risks, including privacy breach incidents, which may be insufficient to indemnify against all arising losses or types of claims.

In addition to the risk of cyber-attacks, we face system availability risk. Our business relies heavily on various IT and application systems. We have robust business continuity plans designed to minimize the duration and impact of an unexpected loss of availability of any of these systems. Nevertheless, we could experience an event that impacts one or more of these systems, including those based in facilities where our vendors or we operate. This may interrupt our ability to conduct business and negatively impact our results of operations, despite our business continuity plans.

Our long-term strategy to deploy operational leverage is dependent on the success of our risk management strategies, and their failure could have a material adverse effect on our financial condition or results of operations.

As an insurer, we assume risk from our policyholders. Our long-term strategy includes using above-average operational leverage compared to the U.S. standard commercial and personal lines industry average, measured as the ratio of NPW to our equity or statutory surplus. We balance and mitigate our operational leverage risk with several risk management strategies within our insurance operations to achieve a balance of growth and profit, including an underwriting risk appetite focused on small-to-medium-sized accounts. We accomplish this by employing significant reinsurance, a disciplined reserving approach, and a conservative investment philosophy. These strategies have inherent limitations. We cannot be certain that an event or series of unanticipated events will not occur and result in greater than expected losses. Given our higher-than-industry average operating leverage, an event or series of unanticipated events could have a more material adverse effect on our results of operations, liquidity, financial condition, financial strength, and debt ratings compared to our industry.

Item 1B. Unresolved Staff Comments.

None.

Item 1C. Cybersecurity.

Risk Management and Strategy

Our business heavily relies on various IT and application systems that contain proprietary and confidential information about our operations, employees, agents, claimants, customers, and their employees and property, including personally identifiable information. These systems are connected to and/or accessed from the Internet, making them susceptible to cyber-attacks. A cyber-attack on our systems, distribution partners and their key operating systems, or any other third-party partners or vendors and their key operating systems may materially affect us. Potential impacts include prolonged interruption of our business operations, reputational harm, or substantial monetary damages. For a detailed description of the risks related to cybersecurity, refer to the "Risks Related to our General Operations" section in Item 1A. "Risk Factors." of this Form 10-K.

We have a dedicated unit, led by the Senior Vice President ("SVP") of Enterprise Strategy and Execution, to implement cybersecurity controls, assess and report on cybersecurity risks, and consult with our ERM unit, which is responsible for identifying, measuring, monitoring, and reporting on key enterprise-wide risks, including cybersecurity risks.

We work with industry-leading security consulting and technology partners and employ a "defense-in-depth" approach that uses multiple security measures to protect the integrity of our proprietary and confidential information. This approach aligns with the National Institute of Standards and Technology Cyber Security Framework and provides preventative, detective, and responsive measures to identify and manage risks. We periodically review our strategy and modify its implementation based on threat trends, program maturity, the results of assessments, and the advice of third-party security consultants. We have documented policies, procedures, and guidelines related to information security, known as our "Written Information Security Program." Our program (i) balances responsiveness to rapidly changing threats with ensuring our IT security environment's sustainability and overall effectiveness and (ii) is reasonably likely to defend against risks of cybersecurity threats that would have a material impact on our business strategy, results of operations, or financial condition. This program focuses on the following six key areas used to monitor various IT performance and security metrics:

•Proactive cybersecurity processes, including vulnerability scanning, penetration testing, and periodic program assessments by outside security consultants and assessors;

•Reactive cybersecurity processes that we regularly evaluate using incident response and disaster recovery exercises based on realistic scenarios;

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•Endpoint technology that includes encryption, threat management, monitoring, investigation support, and backups;

•Identity and access management controls that often include multi-factor authentication and additional safeguards for staff granted elevated privileges;

•Employee cyber risk awareness and training that covers cybersecurity threats and actions to prevent or report attacks; and

•Third-party risk management and security standards, including due diligence, continuous monitoring, cyber risk scoring, and contractual obligations. We review third-party control environments when possible and practical, aligning the risk exposure with our business requirements and risk tolerances.

Board Governance and Management

The Executive Vice President ("EVP") & Chief Information Officer ("CIO") and the SVP of Enterprise Strategy and Execution provide quarterly written and in-person updates on the strength of our cyber risk control environment, emerging cyber threat issues, and the results of external assessments by outside security consultants and assessors to the Board’s Audit Committee, which was responsible for the oversight of our ERM process in 2023. Effective January 1, 2024, the Board created a Risk Committee responsible for oversight of our ERM framework and practices, and to assist the Board in overseeing our operational activities and identifying and reviewing related risks, including our cyber risks and strategy.

In addition, the cybersecurity team, managed by the SVP of Enterprise Strategy and Execution, receives oversight and executive support through engagement with our ERC. The ERC is responsible for the holistic evaluation, management, and supervision of our aggregate risk profile. Similarly, the team works with our ERM function on business alignment and procuring cybersecurity insurance.

The following describes the expertise of key members of management and our committees who are responsible for assessing, managing, and presenting quarterly updates to the Board’s Risk Committee about our cybersecurity risks:

•John Bresney, EVP & CIO, reports directly to our Chief Executive Officer and is responsible for all of our IT operations, including oversight of the SVP of Enterprise Strategy and Execution’s implementation of our cybersecurity program and enforcement of our cybersecurity policies. We have employed him for approximately 30 years, and he has held various technology and information security roles of increasing responsibility. He has a bachelor’s degree in information systems and business, a Master’s Certificate in Project Management, and a Columbia University CIO Program Certificate.

•Robert McKenna, SVP of Enterprise Strategy and Execution, reports to our CIO and leads the implementation of our cybersecurity program, enforcement of our cybersecurity policies, technology planning, projects driving IT strategy, and enterprise IT risk management. He also oversees cybersecurity incidents under our Security Incident Response Plan ("IRP"). We have employed him for approximately 21 years in related positions of increasing responsibility. He has over 27 years of technology and information security experience. He has a master’s degree in business administration, a Certificate in Project Management, and is a Certified Insurance Counselor.

•Christopher Cunniff, SVP and CRO, reports formally to the Chief Financial Officer and on an interim-basis to our Chief Executive Officer, leads our Reinsurance and ERM teams, and chairs the ERC and the Emerging Risk Committee. We have employed him for approximately six years, and he previously was our SVP of Actuarial Reserving. He has over 32 years of insurance industry experience, serving in various key leadership positions. He has a bachelor’s degree in mathematics, is a fellow of the Casualty Actuarial Society, and is a member of the American Academy of Actuaries.

Our IRP describes the circumstances that require internal and external notifications of cybersecurity incidents that (i) relate to any of our computer systems or networks and compromise the confidentiality, integrity, or availability of the systems or networks, (ii) compromise the confidentiality, integrity, or availability of any sensitive data that belongs to us or a third party and is in our care or custody, or (iii) involve one or more third parties with whom we share sensitive data. It describes the (i) involvement of the SVP of Enterprise Strategy and Execution, (ii) escalation process of such incidents to senior management, including the General Counsel, CIO, Chief Financial Officer, CRO, and Chief Executive Officer, (iii) reporting process to the Risk Committee and Board, and (iv) the notification and disclosure process to customers, distribution partners, regulators, and

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the SEC. The IRP also provides guidance on how to evaluate potential cyber events and suspicious cyber occurrences. We engage outside legal counsel and technical experts to regularly review the IRP and use internal teams and outside advisors with specialized skills to support the response and recovery efforts of proprietary and confidential information.

For additional information on our overall corporate governance structure and internal process of assessing our other significant risks, see the "Corporate Governance, Sustainability and Social Responsibility" section in Item 1. "Business." of this Form 10-K.

Item 2. Properties.

Our headquarters is a 315,000-square-foot building on an owned 56-acre site zoned for office and professional use in Branchville, New Jersey. We lease all our other operating facilities from unrelated parties. The principal office locations of our insurance operations are listed in the "Geographic Markets" section of Item 1. "Business." of this Form 10-K. Our Investments operations are principally located in leased space in Farmington, Connecticut. Our facilities provide adequate space for our present needs. Additional space should be available on reasonable terms, if needed.

Item 3. Legal Proceedings.

Incidental to our insurance operations, we are routinely engaged in legal proceedings with inherently unpredictable outcomes that could have a material adverse effect on our consolidated results of operations or cash flows in particular quarterly or annual periods. For additional information regarding our legal risks, refer to Item 1A. "Risk Factors." and Note 21. "Litigation" included in Item 8. "Financial Statements and Supplementary Data." of this Form 10-K. As of December 31, 2023, we have no material pending legal proceedings that could have a material adverse effect on our consolidated financial condition, results of operations, or cash flows.

Item 4. Mine Safety Disclosures.

Not applicable.

PART II

Item 5. Market For Registrant’s Common Equity, Related Stockholder Matters and Issuer Purchases of Equity Securities.

(a) Market Information

Our common stock is traded on the Nasdaq Global Select Market under the symbol "SIGI."

(b) Holders

Our transfer agent’s records reflect that we had 2,783 common stockholders of record as of January 31, 2024.

Dividends on shares of our common stock are declared and paid at the discretion of the Board of Directors (the "Board") based on our results of operations, financial condition, capital requirements, contractual restrictions, and other relevant factors. We expect to continue to pay quarterly cash dividends on shares of our common stock.

On November 1, 2023, the Board approved a 17% increase in our common stock dividend to $0.35 per share. On January 31, 2024, the Board declared a $0.35 per share quarterly cash dividend on common stock payable March 1, 2024, to stockholders of record as of February 15, 2024.

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(d) Securities Authorized for Issuance under Equity Compensation Plans

The following table provides information about our common stock authorized for issuance under equity compensation plans as of December 31, 2023:

(a) (b) (c)

Equity compensation plans approved by security holders — $ — 4,877,332

1Includes 1,049,788 shares available for issuance under our Employee Stock Purchase Plan (2021); 1,508,712 shares available for issuance under the Stock Purchase Plan for Independent Insurance Agencies; and 2,318,832 shares for issuance under the Selective Insurance Group, Inc. 2014 Omnibus Stock Plan ("Stock Plan"). Future grants under the Stock Plan can be made, among other things, as stock options, restricted stock units, or restricted stock.

(e) Performance Graph

The following chart, produced by Research Data Group, Inc., depicts our performance for the period beginning December 31, 2018, and ending December 31, 2023, comparing total stockholder return on our common stock to the total return of (i) the NASDAQ Composite Index and (ii) a select group of peer companies comprised of NASDAQ-listed companies in SIC Code 6330-6339, Fire, Marine, and Casualty Insurance.

We have not incorporated this performance graph into any other filings we have made with the SEC. Unless we specifically state otherwise, it will not be incorporated by reference into any future SEC filings. This performance graph shall not be deemed "soliciting material" or be "filed" with the SEC unless we specifically request so or incorporate it by reference in any SEC filings we make.

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(f) Purchases of Equity Securities by the Issuer and Affiliated Purchasers

The following table provides information about our purchases of our common stock in the fourth quarter of 2023:

1We purchased these shares from employees to satisfy tax withholding obligations associated with the vesting of their restricted stock units.

2On December 2, 2020, we announced our Board authorized a $100 million share repurchase program with no set expiration or termination date. Our repurchase program does not obligate us to acquire any particular amount of our common stock. Management will determine the timing and amount of any share repurchases under the authorization at its discretion based on market conditions and other considerations.

Item 6. Reserved.

Not applicable.

Item 7. Management’s Discussion and Analysis of Financial Condition and Results of Operations.

Forward-Looking Statements

The terms "Company," "we," "us," and "our" refer to Selective Insurance Group, Inc. (the "Parent"), and its subsidiaries, except as expressly indicated or the context otherwise requires. Certain statements in this Annual Report on Form 10-K, including information incorporated by reference, are “forward-looking statements” defined in the Private Securities Litigation Reform Act of 1995 (“PSLRA”). The PSLRA provides a forward-looking statement safe harbor under the Securities Act of 1933 and the Securities Exchange Act of 1934. These statements discuss our intentions, beliefs, projections, estimations, or forecasts of future events and financial performance. They involve known and unknown risks, uncertainties, and other factors that may cause our or our industry's actual results, activity levels, or performance to materially differ from those in or implied by the forward-looking statements. In some cases, forward-looking statements include the words “may,” “will,” “could,” “would,” “should,” “expect,” “plan,” “anticipate,” “target,” “project,” “intend,” “believe,” “estimate,” “predict,” “potential,” “pro forma,” “seek,” “likely,” “continue,” or comparable terms. Our forward-looking statements are only predictions; we cannot guarantee or assure that such expectations will prove correct. We undertake no obligation to publicly update or revise any forward-looking statements for any reason except as required by law.

We discuss factors that could cause our actual results to differ materially from our project, forecasts, or estimates in forward-looking statements in Item 1A. “Risk Factors.” of this form 10-K. These risk factors may not be exhaustive. We operate in a constantly changing business environment, and new risk factors may emerge at any time. We can neither predict these new risk factors nor assess their impact, if any, on our businesses or the extent to which any factor or combination of factors may cause actual results to differ materially from any forward-looking statements. Given these risks, uncertainties, and assumptions, the forward-looking events we discuss in this report might not occur.

Introduction

We classify our business into four reportable segments:

•Standard Commercial Lines;

•Standard Personal Lines;

•Excess and Surplus Lines ("E&S Lines"); and

•Investments.

For more details about these segments, refer to Note 1. "Organization" and Note 12. "Segment Information" in Item 8. "Financial Statements and Supplementary Data." of this Form 10-K.

We write our Standard Commercial and Standard Personal Lines products and services through nine of our insurance subsidiaries, some of which participate in the federal government's National Flood Insurance Program's ("NFIP") Write Your Own Program ("WYO"). We write our E&S products through another subsidiary, Mesa Underwriters Specialty Insurance Company, a nationally-authorized non-admitted platform for customers who generally cannot obtain coverage in the standard marketplace. Collectively, we refer to our ten insurance subsidiaries as the "Insurance Subsidiaries."

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The following is Management's Discussion and Analysis ("MD&A") of our consolidated financial condition and results of operations. Included in the MD&A is an evaluation of the amounts and certainty of cash flows from operations and outside sources, trends, and uncertainties that may have a material impact in future periods. The MD&A discusses and analyzes our 2023 results compared to 2022. Investors should read the MD&A in conjunction with Item 8. "Financial Statements and Supplementary Data." of this Form 10-K. For discussion and analysis of our 2022 results compared to 2021, refer to Item 7. "Management’s Discussion and Analysis of Financial Condition and Results of Operations." of our Annual Report on Form 10-K for the fiscal year ended December 31, 2022.

In the MD&A, we will discuss and analyze the following:

•Critical Accounting Policies and Estimates;

•Financial Highlights of Results for Years Ended December 31, 2023, 2022, and 2021;

•Results of Operations and Related Information by Segment;

•Federal Income Taxes; and

•Liquidity and Capital Resources.

Critical Accounting Policies and Estimates

We have identified the policies and estimates critical to our business operations and the understanding of our results of operations. The policies and estimates we considered most critical to the preparation of the Financial Statements involved (i) reserves for loss and loss expense, (ii) investment valuation and the allowance for credit losses on available-for-sale ("AFS") fixed income securities, and (iii) reinsurance.

Reserves for Loss and Loss Expense

Significant time can elapse between the occurrence of an insured loss, the reporting of the claim to us, and the final settlement and payment of the claim. Insurers establish reserves as balance sheet liabilities to recognize liabilities for unpaid loss and loss expense. The following tables provide case and incurred but not reported ("IBNR") reserves for loss and loss expenses and reinsurance recoverable on unpaid loss and loss expense as of December 31, 2023 and 2022:

Loss and Loss Expense Reserves

1Includes our flood loss exposure related to our participation in the NFIP's WYO program, to which we cede 100% of our flood losses.

2Includes general liability (97% of net reserves) and commercial auto liability coverages (3% of net reserves).

3Includes commercial property (90% of net reserves) and commercial auto property coverages (10% of net reserves).

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Loss and Loss Expense Reserves

1Includes our flood loss exposure relates to our participation in the NFIP's WYO program, to which we cede 100% of our flood losses.

2Includes general liability (96% of net reserves) and commercial auto liability coverages (4% of net reserves).

3Includes commercial property (90% of net reserves) and commercial auto property coverages (10% of net reserves).

The Insurance Subsidiaries' net loss and loss expense reserves duration was approximately 3.1 years at both December 31, 2023 and December 31, 2022.

How reserves are established

Reserve for loss and loss expense include case reserves on reported claims and IBNR reserves. Case reserves are estimated for each individual claim based on facts and circumstances known at the time. Case reserves may be adjusted up or down as the claim's specific facts and circumstances change. IBNR reserves are established at more aggregated levels and include provisions for (i) claims not yet reported, (ii) future development on reported claims, (iii) closed claims that could reopen in the future, and (iv) anticipated salvage and subrogation recoveries.

We perform quarterly internal reserve reviews using our own loss experience, with consideration given to various internal and external factors. Changes in claim dynamics may inherently alter paid and reported development patterns. While the selections in our reserve analyses aim to account for these impacts, estimated reserves involve an increased risk of variability. In addition to our internal reserve reviews, an external consulting actuary performs an independent semiannual review of our reserves. We do not rely on the external consulting actuary's report to determine our recorded reserves; however, we review and discuss our observations on trends, key assumptions, and actuarial methodologies with our consulting actuary. While not required, our independent consulting actuary issues the annual statutory Statements of Actuarial Opinion for our Insurance Subsidiaries. For additional information on our accounting policy for reserve for loss and loss expense, refer to Note. 2. "Summary of Significant Accounting Policies" in Item 8. "Financial Statements and Supplementary Data." of this Form 10-K.

Range of Reasonable Reserve Estimates

We have estimated a range of reasonable reserve estimates for net loss and loss expense of $4,253 million to $5,004 million at December 31, 2023. This range reflects low and high reasonable reserve estimates determined by judgmentally adjusting the methods, factors, and assumptions selected within the internal reserve review. This approach produces a range of reasonable reserve estimates but does not represent a distribution of all possible outcomes. Therefore, the final outcomes may be greater than or less than these amounts.

The range of reasonable reserve estimates increased as of December 31, 2023, relative to December 31, 2022. This increase was primarily related to reserve growth commensurate with our net premiums earned ("NPE") growth.

Changes in Reserve Estimates (Loss Development)

Our quarterly reserving process may lead to changes in the recorded reserves for prior accident years, referred to as favorable or unfavorable prior year loss and loss expense development. In 2023, we experienced net unfavorable prior year loss

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development of $10.0 million, compared to net favorable development of $78.9 million in 2022 and $82.9 million in 2021. The following table summarizes prior year development by line of business:

(Favorable)/Unfavorable Prior Year Loss and Loss Expense Development

Businessowners' policies 7.6 (7.3) (0.4)

Commercial property 0.7 (1.6) (2.6)

Bonds — (10.0) —

E&S casualty lines (5.0) (5.0) (7.0)

E&S property lines (1.6) (2.5) (0.8)

A detailed discussion of recent reserve development by line of business follows.

Standard Market General Liability Line of Business

At December 31, 2023, our general liability line of business had recorded reserves, net of reinsurance, of $1.9 billion, representing 41% of our total net reserves. In 2023, this line experienced unfavorable reserve development of $55.0 million, attributable to social inflationary impacts driving increased loss severities in accident years 2015 through 2020. We see these social inflationary impacts as an industry dynamic with higher propensity for attorney representation and litigation, longer settlement times, and higher settlement values. In 2022, this line experienced favorable development of $5.0 million, attributable to favorable inception-to-date claim frequencies in accident years 2020 and 2021.

This line of business has experienced a long-term historical trend of meaningful severity increases, largely offset by decreases in claim frequencies. In response to potentially increasing social inflationary impacts, we have been embedding higher severity assumptions in our initial loss ratio estimates in recent years, which are materializing in actual results. The trend of lower frequencies has continued, while prior year severities have developed adversely. Despite this, initial estimates for less mature accident years have remained stable. However, if the favorable frequency trend moderates or severities continue to emerge higher than expected, there could be impacts to ultimate loss estimates for this line.

The general liability line of business presents a diverse set of exposures. Various factors influence losses and loss trends, including legislative enactments, judicial decisions, and economic and social inflation. Economic inflation directly impacts our claims severities by increasing the costs of raw materials, medical procedures, and labor. Social inflation may impact both the frequency and severity of claims by affecting (i) the propensity for a claimant to file a claim, (ii) the percentage of claimants who engage lawyers, and (iii) the nature of judicial verdicts, broader liability interpretations, and amounts of associated awards, which influence future settlement values. We monitor claim litigation rates regularly. We have observed modest increases in the percentage of claims with attorney involvement in recent periods, partly due to more litigious coverages, such as management liability coverage. This trend and the impact of previous court closures continue to affect the time to settle claims.

We have exposure to abuse or molestation claims, mainly through insurance policies that we (i) underwrite through our Community and Public Services ("CAPS") strategic business unit and (ii) issue to schools, religious institutions, day-care facilities, and other social services. These customers within our CAPS business unit represented approximately 10% of our total Standard Commercial Lines NPW in 2023 and 2022. We continue to actively manage policy limits and monitor each jurisdiction's statute of limitations to ensure our rate level accounts for the changing exposure, to the extent regulatorily possible. While these underwriting and pricing actions have been necessary to position the portfolio for future profitability, they have limited our CAPS growth in recent years.

We also have exposure to abuse or molestation claims from enacted state laws that extend the statute of limitations or permit windows for abuse or molestation claims and lawsuits that statutes of limitations previously barred. Consequently, we may receive claims decades after the alleged acts involving complex claims coverage determinations, potential litigation, higher defense costs, and the need to collect from reinsurers under older reinsurance agreements. Our claims and actuarial departments actively monitor these claims to identify changes in frequency or severity and any emerging or shifting trends.

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While this should help us better understand this rapidly evolving exposure, the ultimate impact of social, political, and legal trends remains highly uncertain, which could significantly impact the ultimate settlement values for these claims.

Standard Market Workers Compensation Line of Business

At December 31, 2023, our workers compensation line of business had recorded reserves, net of reinsurance, of $804 million, representing 17% of our total net reserves. During 2023, this line experienced favorable reserve development of $74.5 million, primarily due to improved loss severities in accident years 2021 and prior. Similarly, this line experienced favorable reserve development during 2022 of $70.0 million related to favorable inception-to-date claim frequencies in accident year 2020 and improved loss severities in accident years 2020 and prior. During both 2023 and 2022, the lower-than-expected loss emergence was partly due to (i) medical inflation that was lower than initially anticipated and (ii) various claims initiatives we have implemented. Because of the length of time injured workers can receive related medical treatment, decreases in medical inflation can cause favorable loss development over an extended number of accident years.

A variety of issues can impact the workers compensation line of business, such as:

Unexpected changes in medical cost inflation – The industry currently is experiencing an extended period of lower medical claim cost inflation. However, medical costs are beginning to rise, though to a lesser degree than the recent elevated economic inflation measured by the Consumer Price Index. Offering some protection are wage increases, which are used as the rating basis for workers compensation coverage and continue to outpace medical inflation. Changes to our historical workers compensation medical costs and potential changes in future medical inflation can add reserve variability;

Changes in statutory workers compensation benefits – Statutory benefit changes may affect all outstanding claims, including past and not-yet-settled claims. Depending on the social and political climate, these changes may either increase or decrease associated claim costs; and

Changes in utilization of the workers compensation system –These changes may be driven by economic, legislative, or other changes, like increased prescriptions for pharmaceuticals, more complex medical procedures, changes in permanently injured workers' life expectancy, and health insurance availability.

Standard Market Commercial Automobile Line of Business

At December 31, 2023, our commercial automobile line of business had recorded reserves, net of reinsurance, of $959 million, representing 20% of our total net reserves. In 2023, this line experienced unfavorable prior year reserve development of $8.0 million, primarily due to increased loss expenses in accident years 2022 and prior. In 2022, this line experienced unfavorable prior year reserve development of $22.5 million, driven by increased severities in the 2021 accident year.

The commercial automobile line has experienced unfavorable trends in recent years that has negatively affected results for us and the industry. Pre-pandemic, increased frequencies were attributable to increased miles driven, likely related to lower unemployment, poor road quality, and increased distracted driving. The pandemic and the governmental "stay-at-home" orders issued in early 2020 dramatically reduced miles driven and road traffic, significantly reducing claims frequency that year. At the same time, the industry reported dramatic increases in risky driving behaviors, such as speeding, distracted driving, and driving under the influence. In addition, traffic deaths per mile driven increased significantly. With increased miles driven in subsequent years, fatality rates per mile driven have tempered but remain well above pre-pandemic levels. Risky driving behaviors and the impacts of social inflation continue to pressure this line's claim severities. As of year-end 2023, frequencies remained somewhat below pre-pandemic levels due to changes in commuting patterns.

Increased property damage and physical damage severities relate to (i) elevated repair costs for increasingly complex vehicles that incorporate more technology, (ii) extended periods of rental reimbursement costs for claims, and (iii) inflationary impacts and disruptions to the supply chain, although these have moderated in recent quarters.

Over the last several years, we have taken actions to improve the profitability of this line of business, including:

•Taking meaningful rate and underwriting actions on our renewal portfolio. We continue to leverage our predictive modeling and analytical capabilities that provide guidance and automatic retrieval of relevant public information on existing and potential policyholders to provide more granular insights about where we should focus our actions.

•Reducing premium leakage by improving the quality of our rating information, including validating application information with third-party data and obtaining more detailed vehicle usage information.

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•Aggressively managing new business pricing and hazard mix. Deploying co-underwriting by our regional underwriters and corporate underwriting teams' subject matter experts for selected higher hazard classes to improve risk-driver recognition and exposure-based pricing.

Standard Market Personal Automobile Line of Business

At December 31, 2023, our personal automobile line of business had recorded reserves, net of reinsurance, of $130 million, representing 3% of our total net reserves. This line experienced unfavorable prior year reserve development of $15.3 million in 2023, primarily due to increased loss severities in accident year 2022. This line experienced modest unfavorable prior year reserve development of $0.5 million in 2022.

Some of the same issues affecting the commercial automobile line also impact this line. The COVID-19-related frequency reduction was even more pronounced for the personal automobile line than the commercial automobile line. Frequencies rebounded post-pandemic and have nearly returned to pre-pandemic levels. In addition to the COVID-19-related temporary impacts, the underlying trends of increased vehicle repair costs and poor road quality are likely causes of rising severities, exacerbated by riskier driving behaviors, including distracted driving trends. We continue recalibrating our predictive models and refining our underwriting and pricing approaches, including prioritizing rate filings state-by-state, to mitigate these rising severities. These filed rate increases began to take effect on a written basis during the first quarter of 2023 and continued to take effect through the end of 2023. We expect the number of rate filings and their rate impacts to continue to increase throughout 2024. While we believe these underwriting and pricing changes will ultimately lead to improved profitability and greater stability, the resulting changes to our exposure profile may impact paid and reported development patterns, increasing the uncertainty in the reserves in the near-term.

E&S Casualty Lines of Business

At December 31, 2023, our E&S casualty lines of business had recorded reserves, net of reinsurance, of $532 million, representing 11% of our total net reserves. Our E&S casualty lines results have improved over recent years. In 2023, this line experienced favorable prior year reserve development of $5.0 million, primarily due to improved loss severities in accident years 2021 and prior. In 2022, this line experienced favorable prior year reserve development of $5.0 million, primarily attributable to favorable policy inception-to-date claim frequencies and improved loss severities in accident years 2020 and 2021.

Some of the risk factors for the general liability line also affect the E&S casualty lines. These include (i) economic inflation, such as materials and labor costs and (ii) social inflationary trends, such as increased attorney involvement, broader liability findings, and more generous settlement awards.

We made underwriting operational changes that improved E&S casualty lines performance. Before 2023, our underwriting operations had substantially exited several targeted business classes with historically volatile results, including commercial automobile liability, liquor liability, and snow removal. We have shifted more policy acquisitions to middle market business without materially increasing the portfolio's overall risk profile.

The following E&S casualty claims operational changes have created further casualty improvements:

•We created a dedicated E&S claims team in our corporate claims function, bringing greater expertise and consistency to E&S claims handling.

•We created separate specialized claims teams for "litigated," "non-litigated," and "high exposure" claims.

•We implemented the following legal operational and expense improvement initiatives:

◦Increased the use of employed staff counsel lawyers to defend covered claims litigation;

◦Consistent with our policies' terms related to covered claims, the duty to defend, and regulatory standards, enhanced processes for legal budgeting and expense management; and

◦Implemented a process to review the effectiveness of outside counsel defending our insureds.

While we believe these underwriting and claims operational changes have improved our underwriting experience, these changes have inherent risks. Changes in portfolio composition or our claims processes may affect paid and reported development patterns. While our reserve analyses incorporate methods that adjust for these changes, estimated reserves have a greater risk of fluctuation.

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Other impacts that create additional loss and loss expense reserve uncertainty

Claims Initiative Impacts

Our Claims Department continually identifies areas for improvement and efficiency to increase our value proposition to policyholders. These improvements may lead to claims practice changes affecting average case reserve levels and claims settlement rates, directly impacting the data used to project ultimate loss and loss expense. While these changes may increase uncertainty in our estimates in the short term, we expect refined claims process management to be the longer-term benefit.

Our internal reserve analyses incorporate actuarial projection methods that make adjustments for changes in case reserve adequacy and claims settlement rates. These methods adjust our historical loss experience to the current case adequacy or settlement rate level, providing a more consistent basis for projecting future development patterns. Like all projection methods, these have their own associated assumptions and judgments. Accordingly, no single method can be considered definitive.

Unanticipated Changes in Economic Inflation

United States ("U.S.") monetary policy and global economic conditions bring additional uncertainty related to inflationary trends. Changes in inflation affect the ultimate settlement costs for many of our lines of business, with the greatest reserve impact on the longer-tailed lines, such as general liability and workers compensation. Uncertainty about future inflation or deflation creates the potential for additional reserve variability in these lines of business.

Sensitivity analysis: Potential impact on reserve estimates due to changes in key assumptions

Our process to establish reserves includes a variety of key assumptions, such as:

•The selection of loss and loss expense development factors;

•The weight applied to each individual actuarial projection method;

•Projected future loss trends; and

•Expected claim frequencies, severities, and ultimate loss and loss expense ratios for the current accident year.

The importance of any single assumption depends on several considerations, such as line of business and accident year. If the actual experience emerges differently than the assumptions underlying the reserve process, possible changes in our reserve estimates could be material to the results of operations in future periods. Below are sensitivity tests highlighting potential impacts to loss and loss expense reserves for the major casualty lines of business under different scenarios. These tests consider each assumption and line of business individually without considering the correlation between lines of business and accident years. Therefore, the results do not constitute an actuarial range. While the figures represent possible impacts from variations in certain key assumptions, there is no assurance that future loss and loss expense emergence will be consistent with our current or alternative assumptions.

Changes in internal and external trends and operational changes may manifest as changes in loss and loss expense development patterns. These patterns are a key assumption in the reserving process. In addition, the current accident year expected loss and loss expense ratios are key assumptions. These ratios are developed through a rigorous process of projecting recent accident years' experience to an ultimate settlement basis. They are then adjusted to the current accident year's pricing and loss cost levels. The impact of underwriting portfolio and claims handling practice changes is also quantified and reflected where appropriate. As with all estimates, the ultimate loss and loss expense ratios may differ from those currently estimated.

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The sensitivities of loss and loss expense reserves to these key assumptions are illustrated below for the major casualty lines. The first table displays estimated impacts from changes in expected reported loss and loss expense development patterns for our major casualty lines of business. It shows line of business reserve impacts if the actual calendar year incurred amounts are greater or less than current expectations by the selected percentages. While judgmental, the selected percentages by line are based on the reserve range analysis and the actual historical reserve development for the line of business. The second table displays the estimated impacts of changes to the expected loss and loss expense ratios for the current accident year. It shows reserve impacts by line of business if the expected loss and loss expense ratios for the current accident year are greater or less than current expectations by the selected percentages.

Reserve Impacts of Changes to Expected Loss and Loss Expense Reporting Patterns

Workers compensation 15 (85) 85

Commercial automobile liability 12 (105) 105

Personal automobile liability 20 (20) 20

Workers compensation 10 (35) 35

Commercial automobile liability 10 (65) 65

Personal automobile liability 10 (10) 10

There is some overlap between the impacts shown in the two tables. For example, increases in the calendar year development would ultimately impact our view of the current accident year's loss and loss expense ratios. However, these tables provide perspective on the sensitivity of each key assumption. While the changes represent outcomes based on reasonably likely changes to our underlying reserving assumptions, they do not represent a range of possible outcomes. Our reserves could increase or decrease significantly from what the tables reflect.

Asbestos and Environmental Reserves

Our general liability, businessowners' policies, and homeowners reserves include exposure to asbestos and environmental claims. The emergence of these claims occurs over an extended period and can be unpredictable. The total recorded net loss and loss expense reserves for these claims were $19.1 million as of December 31, 2023, and $20.3 million as of December 31, 2022, with asbestos claims constituting approximately 18% of these reserves in 2023 and 23% in 2022.

Environmental claims have arisen primarily from insured landfill exposures in municipal government and small non-manufacturing commercial risks, and leaking underground storage tanks under homeowners policies. Asbestos claims have arisen primarily from policies issued to (i) various distributors of asbestos-containing products, such as electrical and plumbing materials and (ii) contractors exposed to or handling asbestos-containing products, such as heating, ventilation, and air conditioning contractors. We handle our asbestos and environmental claims in a centralized and specialized asbestos and environmental claim unit. That unit establishes case reserves on individual claims based on the then-known facts and circumstances, which IBNR reserves supplement.

Estimating IBNR reserves for asbestos and environmental claims is difficult because these claims have delayed and inconsistent reporting patterns. In addition, significant uncertainties are associated with estimating critical reserve assumptions, such as average clean-up costs, third-party costs, potentially responsible party shares, allocation of damages, litigation and coverage costs, and potential state and federal legislative changes.

Other Latent Exposures

We also have other latent and continuous trigger exposures in our ongoing portfolio. Examples include claims for construction defect and abuse or molestation, including in states that have increased and expanded the statute of limitations. We manage our exposure to these liabilities through our underwriting and claims practices and a dedicated claims unit, similar to our handling of asbestos and environmental claims. The impact of social, political, and legal trends on these claims remains highly uncertain, so the adequacy of our related loss and loss expense reserves to cover these claims remain highly uncertain. These exposures remain in our ongoing portfolio and are reserved in aggregate, with other exposures within the line of business

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reserves.

Investment Valuation and the Allowance for Credit Losses on AFS Fixed Income Securities

Investment Valuation

Accounting guidance defines the fair value of our investment portfolio as the exit price or amount that would be (i) received to sell an asset or (ii) paid to transfer a liability in an orderly transaction between market participants. When determining an exit price, we must rely on observable market data, if available. Most securities in our equity portfolio have readily determinable fair values and are recorded at fair value with changes in unrealized gains or losses recognized through income. Our AFS fixed income securities portfolio is recorded at fair value, and the related unrealized gains or losses are reflected in stockholders' equity, net of tax. For our AFS fixed income securities portfolios, fair value is a key factor in the measurement of (i) losses on securities for which we have the intent to sell, and (ii) changes in the allowance for credit losses.

The fair value of approximately 91% of our investments measured at fair value are classified as either Level 1 or Level 2 in the fair value hierarchy and are priced using observable inputs for identical or similar assets. About 9% are classified as either (i) Level 3 and are based on unobservable market inputs because the related securities are not traded on a public market, or (ii) not leveled because the related securities are measured at fair value using net asset value per share (or its practical expedient). For additional information, refer to the following sections within Item 8. "Financial Statements and Supplementary Data." of this Form 10-K: (i) item (d) of Note 2. "Summary of Significant Accounting Policies" for descriptions of the levels within the fair value hierarchy and the valuation techniques used for our Level 3 securities, and (ii) Note 7. "Fair Value Measurements" for quantitative information on the unobservable inputs in our securities measured using Level 3 inputs.

Allowance for Credit Losses on AFS Fixed Income Securities

When fixed income securities are in an unrealized loss position and we do not intend to sell them, we record an allowance for credit losses for the portion of the unrealized loss related to an expected credit loss. We estimate expected credit losses on these securities by performing a risk-adjusted discounted cash flow ("DCF"). The allowance for credit losses is the excess of amortized cost over the greater of (i) our estimate of the present value of expected future cash flows or (ii) fair value. The allowance for credit losses cannot exceed the unrealized loss, and therefore it may fluctuate with changes in the security's fair value. We also consider the need to record losses on securities in an unrealized loss position for which we have the intent to sell.

We analyze unrealized losses for credit loss in accordance with our existing accounting policy, which includes performing DCF analyses on securities at the lot level and analyzing these DCFs using various economic scenarios. In performing these DCF analyses, we calculate the present value of future cash flows using various models specific to the major security types in our portfolio. These models use security-specific information and forecasted macroeconomic data to determine possible expected credit loss scenarios based on projected economic changes. The forecasted economic data incorporated into the models is based on the Federal Reserve Board’s annual supervisory stress test review on certain large banks and financial institutions.

We also can incorporate internally-developed forecast information into the models as we deem appropriate. In developing our best estimate of the allowance for credit losses, we consider our outlook on the probability of the various scenarios occurring.

Based on these analyses, we recorded an allowance for credit losses on our AFS fixed income securities portfolio of $28.2 million at December 31, 2023, and $45.7 million at December 31, 2022. After considering the allowance for credit losses, the remaining unrealized losses on this portfolio were $403.4 million at December 31, 2023 and $537.2 million at December 31, 2022. The decrease in 2023 compared to 2022 was primarily driven by a decrease in benchmark U.S. Treasury rates and, to a lesser extent, a tightening of credit spreads. If the security-specific and macroeconomic assumptions in our DCF analyses or our outlook on the occurrence probability of our DCF model scenarios were to change, our allowance for credit losses and the resulting credit loss expense or benefit will negatively or positively impact our results of operations. Factors considered in determining the allowance for credit losses require significant judgment, including our evaluation of the security's projected cash flow stream.

For additional information regarding our allowance for credit losses on AFS fixed income securities, see item (c) of Note 2. "Summary of Significant Accounting Policies" and item (i) of Note 5. "Investments" within Item 8. "Financial Statements and Supplementary Data." of this Form 10-K, respectively.

Reinsurance

Reinsurance recoverables on paid and unpaid loss and loss expense represent our estimates of the amounts we will recover from reinsurers. Each reinsurance contract is analyzed to ensure sufficient risk is transferred to record the transactions appropriately as reinsurance in the Financial Statements. Amounts recovered from reinsurers are recognized as assets contemporaneously and

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in a manner consistent with the paid and unpaid losses associated with the reinsured policies. An allowance for credit losses on our reinsurance recoverable balance is recorded based on an evaluation of balances due from reinsurers and other available information, including collateral we hold under the terms and conditions of the underlying agreements. Reinsurers often purchase and rely on their retrocessional reinsurance programs to manage their capital position and improve their financial strength ratings. Details about retrocessional reinsurance programs are not always transparent, making it difficult to assess our reinsurers' exposure to counterparty credit risk. Other factors impact our reinsurer's credit quality, such as their reserve adequacy, investment portfolio, regulatory capital position, catastrophe aggregations, and risk management practices. In addition, contractual language interpretations and willingness to pay valid claims can impact our allowance for estimated uncollectible reinsurance. Our allowance for estimated uncollectible reinsurance was $1.7 million at December 31, 2023, and $1.6 million at December 31, 2022. We continually monitor developments that may impact recoverability from our reinsurers, for which we have contractual remedies if necessary. For further information regarding reinsurance, see the "Reinsurance" section below in "Results of Operations and Related Information by Segment" and Note 9. "Reinsurance" in Item 8. "Financial Statements and Supplementary Data." of this Form 10-K.

Financial Highlights of Results for Years Ended December 31, 2023, 2022, and 20211

Financial Data:

Key Metrics:

Per Common Share Amounts:

Dividends declared per share to common stockholders 1.25 1.14 10 1.03 11

Non-GAAP Information2:

Non-GAAP operating income per diluted common share 5.89 5.03 17 6.27 (20)

1Refer to the Glossary of Terms attached to this Form 10-K as Exhibit 99.1 for definitions of terms used in this financial review.

2Non-GAAP operating income, non-GAAP operating income per diluted common share, and non-GAAP operating ROE are measures comparable to net income available to common stockholders, net income available to common stockholders per diluted common share, and ROE, respectively, but exclude after tax net realized and unrealized gains and losses on investments included in net income. Adjusted book value per common share is a measure comparable to book value per common share, but excludes total after-tax unrealized gains and losses on investments included in accumulated other comprehensive income (loss). These non-GAAP measures are important financial measures that we, analysts, and investors use because the timing of realized and unrealized investment gains and losses on securities in any given period is largely discretionary. In addition, net realized and unrealized investment gains and losses on

investments could distort the analysis of trends.

Reconciliations of our GAAP to non-GAAP measures are provided in the tables below:

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Non-GAAP operating income per diluted common share $ 5.89 5.03 6.27

Reconciliation of ROE to non-GAAP operating ROE 2023 2022 2021

Tax on reconciling items — (1.1) 0.2

The components of our ROE and non-GAAP operating ROE are as follows:

Standard Commercial Lines segment 5.0 % 4.6 0.4 pts 5.9 (1.3) pts

Standard Personal Lines segment (2.5) (0.2) (2.3) 0.1 (0.3)

Net realized and unrealized investment gains (losses) (0.1) (3.6) 3.5 0.5 (4.1)

In 2023, we generated an ROE of 14.3% compared to 8.8% in 2022. Our non-GAAP operating ROE of 14.4% in 2023 was above our target non-GAAP operating ROE of 12% and above our 2022 non-GAAP operating ROE of 12.4%, which marks a significant milestone for us as this was our tenth consecutive year generating double-digit non-GAAP operating ROE. We also exceeded $4 billion of net premiums written ("NPW") for the first time in our nearly 100-year history, as we achieved 16% NPW growth in 2023 compared to 2022. We view our 2023 results as a significant achievement in a year with elevated uncertainty of loss trends influenced by economic and social inflation, the unusual frequency and severity patterns resulting from the pandemic and its longer-term residual impacts, and a heightened frequency of catastrophe losses. Our results reflect the success of our underwriting discipline, active management of our investment portfolio, and profitable growth strategies.

The 2.0-point increase in our non-GAAP operating ROE in 2023, compared to 2022, included the following:

•An increase in after-tax net investment income of $77.3 million, or 3.0 points, in 2023, compared to 2022. The 2023 increase was attributable to greater after-tax net investment income earned on our fixed income securities portfolio. This portfolio benefited from higher book yields we earned on the investment of operating and investing cash flows in the higher interest rate environment over the past two years.

•An increase in Standard Commercial Lines and E&S Lines after-tax underwriting income of $30.1 million, or 1.1 points, in 2023, compared to 2022. These segments represent 90% of our business and delivered underwriting results at or better than our 95% combined ratio target. The 2023 increase was attributable to lower non-catastrophe property loss and loss expenses and improved underwriting expenses, partially offset by higher net catastrophe losses and lower favorable prior year casualty reserve development.

•An increase in Standard Personal Lines after-tax underwriting losses of $56.9 million, or 2.3 points, in 2023, compared

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to 2022, which partially offset the improvements in our other segments. Higher net catastrophe losses and unfavorable prior year casualty reserve development negatively impacted this segment in 2023.

Overall pre-tax net catastrophe losses increased $98.6 million in 2023, compared to 2022. We were impacted by 66 Property Claim Services ("PCS") named events in 2023, compared to 56 in 2022. In addition, favorable prior year casualty reserve development decreased $79.5 million in 2023, compared to 2022, primarily driven by $55 million of unfavorable prior year casualty reserve development in our general liability line of business in 2023 compared to favorable development of $5 million in 2022. While down year-over-year, we reported our 18th consecutive year of net favorable prior year casualty reserve development.

For additional information on our insurance segment results, refer to the insurance segment sections below.

Our ROE was up 3.5 points in 2023 compared to 2022 due to a decrease in net realized and unrealized investment losses. The decrease in net realized and unrealized investment losses was primarily due to (i) a credit loss benefit recorded on our AFS fixed income securities portfolio in 2023, compared to credit loss expense recorded in 2022, and (ii) an increase in valuations reflecting the current public equities market. The 2023 credit loss benefit reflected the decrease in benchmark U.S. Treasury rates and, to a lesser extent, a tightening of credit spreads.

Outlook

2023 marks our tenth consecutive year of double-digit non-GAAP operating ROE. Over those ten years, our operating ROE was 12.2%, exceeding our target of 12%. Our target is set approximately 300 to 400 basis points above our weighted average cost of capital. Throughout the market cycle and under various interest rate environments, we believe a 95% combined ratio should allow us to meet our operating ROE target. Based on current interest rates and the elevated contribution of net investment income to operating ROE, we expect to produce an operating ROE in excess of our target, as was the case in 2023. Our combined ratio target allows us to remain focused on disciplined underwriting and profitable growth while being a stable insurance carrier for our customers and distribution partners.

With our strong capital position and operational results, we are well-positioned to navigate the on-going challenges of elevated economic and social inflation and financial market volatility. In 2024, we will focus on delivering on our strategy for disciplined and profitable growth within our insurance operation segments by:

•Standard Commercial Lines

◦Achieving Standard Commercial Lines renewal pure price increases that reflect our current profitability and forward loss trend expectations;

◦Continuing to expand our Standard Commercial Lines market share by (i) increasing our share towards our 12% target of our agents' premiums, (ii) strategically appointing new agents, and (iii) maximizing new business growth in the small business market through the use of our enhanced small business platform; and

◦Expanding our geographic footprint. In 2022, we began writing Standard Commercial Lines business in Vermont, Alabama, and Idaho. We expect to write new business in West Virginia and Maine in early 2024, and Washington, Oregon, and Nevada in late 2024. Over time, we plan to expand our Standard Commercial Lines footprint into most of the contiguous U.S.

•E&S Lines

◦Achieving E&S Lines renewal pure price increases that reflect our current profitability and forward loss trend expectations; and

◦Continuing to invest in product expansion, risk evaluation, and operational efficiency for middle market E&S accounts.

•Standard Personal Lines

◦Aggressively pursuing profitability on our Standard Personal Lines segment by prioritizing additional rate filings on a state-by-state basis and further refining our pricing factors. These filed rate increases began to take effect early in 2023, increasing in number and magnitude throughout the year, and are expected to continue through 2024. We expect our overall written renewal rate to range from approximately 20% to 25% in 2024, subject to regulatory approvals. In addition, other underwriting actions include the following:

▪Seeking to improve our homeowners line of business profitability through the introduction of new policy terms and conditions, including (i) coverage for older roofs based on depreciation schedules rather than replacement cost, and (ii) implementing mandatory wind/hail deductibles in states exposed to severe convective storms, where allowed by law; and

▪Continuing the migration of our Standard Personal Lines products and services towards customers in

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the mass affluent market, where we believe we can be more competitive with our strong coverage and servicing capabilities.

In addition, we will continue developing our culture centered on the values of diversity, equity, and inclusion that foster innovation, idea generation, and the development of a group of specially trained leaders who can guide us successfully into the future.

For 2024, our full-year guidance is as follows:

•A GAAP combined ratio of 95.5%, including net catastrophe losses of 5.0 points. Our combined ratio estimate assumes no prior year casualty reserve development;

•After-tax net investment income of $360 million that includes $32 million of after-tax net investment income from our alternative investments;

•An overall effective tax rate of approximately 21.0%, which assumes an effective tax rate of 20.5% for net investment income and 21% for all other items; and

•Weighted average shares of 61.5 million on a fully diluted basis, which assumes no share repurchases we may make under our authorization.

Our guidance implies a healthy ROE outlook for 2024 that exceeds our 12% target, with ample runway to continue our trajectory of profitable growth. We have the team, sophisticated tools, and disciplined execution to effectively manage through market dynamics, and believe we are operating from a position of strength.

Results of Operations and Related Information by Segment

Insurance Operations

The following table provides quantitative information for analyzing the combined ratio:

Insurance Operations Results:

Less:

Combined Ratios:

Dividends to policyholders ratio 0.2 0.1 0.1 0.2 (0.1)

The NPW growth of 16% in 2023 compared to 2022 reflected (i) overall renewal pure price increases, and (ii) higher direct new business, as shown in the following table:

Renewal pure price increases 6.8 % 5.1 4.9

Our NPW growth in 2023 also benefited from strong retention and exposure growth on renewal policies.

The increase in NPE in 2023 compared to 2022 resulted from the same impacts to NPW described above.

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Loss and Loss Expenses

The loss and loss expense ratio increased 2.2 points in 2023 compared to 2022, primarily due to the following:

We had higher net catastrophe losses in 2023 compared to 2022. In 2023, 66 PCS named events impacted our footprint, compared to 56 in 2022. In 2023 and 2022, net catastrophe losses primarily impacted our commercial property and homeowners line of business, with 2023 events also impacting our E&S property lines.

Details of the prior year casualty reserve development were as follows:

(Favorable)/Unfavorable Prior Year Casualty Reserve Development

Businessowners' policies — (11.0) (2.0)

Bonds — (10.0) —

Total Standard Commercial Lines (15.5) (81.0) (74.0)

Homeowners — — —

Personal automobile 14.0 — —

Total Standard Personal Lines 14.0 — —

Total (favorable) prior year casualty reserve development $ (6.5) (86.0) (81.0)

(Favorable) impact on loss ratio (0.2) pts (2.5) (2.7)

In addition, the loss and loss expense ratio was impacted by a decrease in current year casualty loss costs of 0.8 points in 2023, compared to 2022, primarily due to the mix of business from the impact of premium growth in 2023 compared to 2022.

For additional qualitative discussion on prior year reserve development, current year casualty loss costs, and non-catastrophe property loss and loss expenses, refer to the insurance segment sections below.

Underwriting Expenses

The underwriting expense ratio decreased 0.9 points in 2023 compared to 2022, primarily due to premium growth outpacing the growth in underwriting expenses.

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Standard Commercial Lines Segment

Insurance Segments Results:

Less:

Combined Ratios:

Dividends to policyholders ratio 0.2 0.2 — 0.2 —

NPW growth of 13% in 2023 compared to 2022 reflected (i) renewal pure price increases, (ii) higher direct new business, and (iii) strong retention as shown in the table below. In addition, NPW growth in 2023 benefited from exposure growth on renewal policies.

For the Year Ended December 31,

Direct new business premiums $ 597.5 $ 512.5

Renewal pure price increases on NPW 7.0 5.4

The increase in NPE in 2023 compared to 2022 resulted from the same impacts to NPW described above.

The 1.0-point increase in the loss and loss expense ratio in 2023 compared to 2022 was primarily driven by the following:

Our loss and loss expenses in 2023 experienced elevated net catastrophe losses compared to 2022, as discussed in the "Insurance Operations" section above. Refer to the line of business sections below for qualitative discussion on the significant drivers of favorable prior year casualty reserve development and non-catastrophe property loss and loss expenses.

In addition, the loss and loss expense ratio was impacted by a decrease in current year casualty loss costs of 1.0 point in 2023 compared to 2022, primarily due to (i) the mix of business from the impact of premium growth in 2023, partially offset by (ii) an increase in current year casualty loss costs in our commercial automobile line of business. Refer to the "Commercial Automobile" section below for a qualitative discussion on these current year loss costs.

The underwriting expense ratio decreased 0.9 points in 2023 compared to 2022, primarily due to premium growth outpacing the growth in underwriting expenses.

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The following is a discussion of our most significant Standard Commercial Lines of business:

General Liability

Renewal pure price increases 5.4 4.5 n/a 4.4 n/a

% of total Standard Commercial Lines NPW 33 33 33

1n/a: not applicable.

NPW growth of 13% in 2023 compared to 2022 benefited from exposure growth on renewal policies, strong retention, renewal pure price increases, and higher direct new business.

The combined ratio increased 4.7 points in 2023 compared to 2022, primarily driven by unfavorable prior year casualty reserve development in 2023, as follows:

($ in millions) (Favorable) Prior Year Casualty Reserve Development

The unfavorable prior year casualty reserve development in 2023 was primarily driven by increased loss severities in accident years 2015 through 2020 attributable to social inflationary impacts. We see this as an industry dynamic with higher propensity for attorney representation and litigation, longer settlement times, and higher settlement values. The 2022 favorable prior year casualty reserve development was primarily attributable to favorable inception-to-date claim frequencies in accident years 2021 and 2020.

This line of business has experienced a long-term historical trend of meaningful severity increases, which have been largely offset by decreases in claim frequencies. In response to potential social inflationary impacts, we have been embedding higher severity assumptions in our initial loss ratio estimates in recent years, which are materializing in actual results. The trend of lower frequencies has continued, while prior year severities have developed adversely. Despite this, initial estimates for less mature accident years have remained stable. However, if the favorable frequency trend moderates and severities continue to emerge higher than expected, there could be impacts on ultimate loss estimates for this line.

The combined ratio was also impacted by a decrease in the underwriting expense ratio of 1.2 points in 2023 compared to 2022, primarily due to premium growth outpacing the growth in underwriting expenses.

Commercial Automobile

Renewal pure price increases 9.8 8.1 n/a 8.3 n/a

% of total Standard Commercial Lines NPW 30 30 30

1n/a: not applicable.

NPW growth of 14% in 2023 compared to 2022 benefited from renewal pure price increases, higher direct new business, and strong retention. The higher new business and strong retention contributed to a 5% growth of in-force vehicle counts as of December 31, 2023, compared to December 31, 2022.

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The combined ratio decreased 4.1 points in 2023 compared to 2022, primarily driven by the following:

Loss and loss expenses in 2023 compared to 2022 experienced (i) lower non-catastrophe property loss and loss expenses, as inflationary and supply chain impacts have moderated, partially offset by (ii) elevated net catastrophe losses, as discussed in the "Insurance Operations" section above.

The unfavorable prior year casualty reserve development in 2023 was primarily due to increased loss expenses in accident years 2022 and prior. The 2022 unfavorable prior year casualty reserve development was primarily due to increased severities in the 2021 accident year.

The combined ratio was also impacted by a decrease in the underwriting expense ratio of 1.0 point in 2023 compared to 2022, primarily due to premium growth outpacing the growth in underwriting expenses.

Commercial Property

Renewal pure price increases 9.8 6.2 n/a 6.0 n/a

% of total Standard Commercial Lines NPW 20 18 18

1n/a: not applicable.

NPW growth of 21% in 2023 compared to 2022 benefited from renewal pure price increases, exposure growth on renewal policies, strong retention, and higher direct new business.

The combined ratio decreased 3.2 points in 2023 compared to 2022, primarily driven by the following:

The lower non-catastrophe property loss and loss expenses were primarily due to lower frequencies compared to 2022. We continue to manage our long-term profitability through (i) price increases and (ii) targeted underwriting actions, including an ongoing focus on appropriate policy terms and conditions and achieving accurate insurance-to-value ratios. The elevated net catastrophe losses are further discussed in the "Insurance Operations" section above.

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Workers Compensation

Renewal pure price increases (decreases) (1.5) (0.5) n/a 0.1 n/a

% of total Standard Commercial Lines NPW 12 12 12

1n/a: not applicable.

NPW decreased 1% in 2023 compared to 2022 due to renewal pure price decreases and a slight decrease in retention.

The combined ratio decreased 1.5 points in 2023 compared to 2022, driven by higher favorable prior year casualty reserve development, as follows:

The favorable prior year casualty reserve development in 2023 was primarily due to improved loss severities driven by continued favorable medical cost trends in accident years 2021 and prior. The favorable prior year casualty reserve development in 2022 was primarily due to continued favorable medical trends in accident years 2020 and prior, and favorable inception-to-date claim frequencies in accident year 2020.

Standard Personal Lines Segment

Insurance Segments Results:

Less:

Combined Ratios:

NPW increased 30% in 2023 compared to 2022, primarily due to (i) higher direct new business, (ii) stronger retention, (iii) renewal pure price increases, (iv) higher homeowners coverage amounts due to inflation adjustments, and (v) higher average policy sizes from our mass affluent market strategy. In the third quarter of 2021, we transitioned our personal lines strategy to targeting customers in the mass affluent market, where we believe our strong coverage and servicing capabilities will be more competitive. Over 65% of new business in our homeowners line of business in 2023 had dwelling coverage values over $500,000.

Direct new business premiums1 $ 116.5 $ 62.9

Renewal pure price increases on NPW 5.2 0.7

1Excludes our flood direct premiums written, which is 100% ceded to the NFIP and therefore, has no impact on our NPW.

The increase in NPE in 2023 compared to 2022 resulted from the same impacts on NPW discussed above.

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The loss and loss expense ratio increased 19.5 points in 2023 compared to 2022, driven by the following:

Net catastrophe losses in both 2023 and 2022 exceeded our 10-year historical average, with 2023 being elevated over 2022, as discussed in the "Insurance Operations" section above.

We experienced elevated non-catastrophe property loss and loss expenses in 2023 compared to 2022, driven by higher personal automobile physical damage losses and homeowners property losses. The higher automobile damage losses resulted from increased claim frequencies, driven in part by increased miles driven. Higher homeowners property losses were attributable to elevated severities due to (i) higher construction costs impacted by economic inflation and (ii) increasing home values due to higher average policy sizes from our mass affluent market strategy.

The unfavorable prior year casualty reserve development in 2023 was primarily attributable to increased loss severities in accident year 2022. There was no prior year casualty reserve development in 2022.

In addition, the loss and loss expense ratio was impacted by a 6.4-point increase in current year casualty loss costs in 2023 compared to 2022 from (i) elevated prior year severities, which influenced our current year severity estimates, and (ii) increased claim frequencies in the current year.

We are aggressively managing this business by continuing to prioritize additional rate filings on a state-by-state basis to mitigate these inflationary impacts, and refining our pricing factors. These filed rate increases began to take effect early in 2023, increasing in number and magnitude throughout the year, and are expected to continue through 2024. We expect our overall written renewal rate to range from approximately 20% to 25%, subject to regulatory approvals. In addition, we are seeking to improve profitability within our homeowners' line of business by introducing new policy terms and conditions, including (i) coverage for older roofs based on a schedule of factors rather than replacement cost and (ii) implementing mandatory wind/hail deductibles in states exposed to severe convective storms, where allowed by law.

E&S Lines Segment

Insurance Segments Results:

Less:

Combined Ratios:

Loss and loss expense ratio 54.3 % 58.8 (4.5) pts 62.6 % (3.8) pts

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NPW growth of 24% in 2023 compared to 2022, reflected renewal pure price increases and higher direct new business as shown in the table below. NPW growth in 2023 also benefited from property and casualty exposure growth on renewal policies driven by higher rates associated with increased construction costs resulting from economic inflation.

Direct new business premiums $ 209.5 156.3

Renewal pure price increases on NPW 6.9 % 7.3

The increase in NPE in 2023 compared to 2022 resulted from the same impacts to NPW discussed above.

The loss and loss expense ratio decreased 4.5 points in 2023 compared to 2022, primarily driven by a 4.6-point decrease in current year casualty loss costs in 2023 compared to 2022. Our E&S casualty lines results have improved over recent years, benefiting from several underwriting and claims initiatives and strong rate increases. The decrease in current year casualty loss costs reflects the impacts of these actions.

In addition, the loss and loss expense ratio was impacted by the following:

We experienced elevated net catastrophe losses in 2023 compared to 2022, as discussed in the "Insurance Operations" section above. The favorable prior year casualty reserve development in 2023 was primarily due to improved loss severities in accident years 2021 and prior. The favorable prior year casualty reserve development in 2022 was primarily attributable to favorable inception-to-date claim frequencies and lower loss severities in accident years 2021 and 2020.

Reinsurance

We use reinsurance to protect our capital resources and insure against losses on property and casualty risks that we underwrite above the amount of losses we are willing to accept. We use two main reinsurance vehicles: (i) a reinsurance pooling agreement among our Insurance Subsidiaries through which each company agrees to share in premiums and losses based on certain specified percentages; and (ii) reinsurance treaties and arrangements with third parties that cover various policies that we issue to our customers.

Reinsurance Pooling Agreement

The primary purposes of the Insurance Subsidiaries' reinsurance pooling agreement are to:

•Pool or share proportionately the underwriting profit and loss results of property and casualty insurance underwriting operations through reinsurance;

•Reduce administration expenses; and

•Permit all the Insurance Subsidiaries to obtain a uniform rating from AM Best Company ("AM Best").

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The following illustrates the pooling percentages by Insurance Subsidiary as of December 31, 2023:

Insurance Subsidiary Pooling Percentage

Selective Insurance Company of America ("SICA") 32.0%

Selective Way Insurance Company ("SWIC") 21.0%

Selective Insurance Company of South Carolina ("SICSC") 9.0%

Selective Insurance Company of the Southeast ("SICSE") 7.0%

Selective Insurance Company of New York ("SICNY") 7.0%

Selective Casualty Insurance Company ("SCIC") 7.0%

Selective Auto Insurance Company of New Jersey ("SAICNJ") 6.0%

Mesa Underwriters Specialty Insurance Company ("MUSIC") 5.0%

Selective Insurance Company of New England ("SICNE") 3.0%

Selective Fire and Casualty Insurance Company ("SFCIC") 3.0%

Reinsurance Treaties and Arrangements

By entering into reinsurance treaties and arrangements, we can increase our underwriting capacity, accepting larger individual risks and aggregations of risks without directly increasing our capital or statutory surplus. Under our reinsurance treaties, we cede to our reinsurers a portion of our incurred losses from an individual policy or group of policies in exchange for a portion of the premium on those policies. Amounts not reinsured below a specified dollar threshold are known as retention. Reinsurance does not legally discharge us from liability under the terms and limits of our policies, but it does make our reinsurers liable to us for the amount of liability we cede to them. Our reinsurers often rely on their own reinsurance programs, or retrocessions, to manage their large loss exposures. The size of the global reinsurance community is relatively small. If our reinsurers cannot collect on their retrocessional programs, it may impair their ability to pay us for the amounts we cede to them.

Consequently, our reinsurers present us with direct, indirect, and contingent counterparty credit risk. We attempt to mitigate this credit risk by (i) pursuing relationships with reinsurers rated “A-” or higher by AM Best and/or (ii) obtaining collateral to secure reinsurance obligations. Some of our reinsurance treaties permit us to terminate or commute them – or require the reinsurer to post collateral if the reinsurer's financial condition or rating deteriorates. We monitor our reinsurers' financial condition and review the quality of reinsurance recoverables and reserves for uncollectible reinsurance. For additional information regarding our reinsurance counterparty credit risk, see Note 9. "Reinsurance" in Item 8. "Financial Statements and Supplementary Data." of this Form 10-K.

We have reinsurance contracts that separately cover our property and casualty insurance business that can be categorized as follows:

•Property Reinsurance, which includes our (i) property excess of loss treaties purchased for protection against large individual property losses and (ii) property catastrophe treaties and a property catastrophe bond transaction to provide protection for the overall property portfolio against severe catastrophic events. We also purchase a limited amount of facultative reinsurance, primarily for large individual property risks greater than our property excess of loss treaty capacity.

•Casualty Reinsurance, which provides protection for both individual large casualty losses and catastrophic casualty losses involving multiple claimants or insureds. We also may use (i) facultative reinsurance, primarily for large individual casualty risks in excess of our treaty capacity and (ii) quota share capacity for certain new or higher severity casualty lines of business.

•Terrorism Reinsurance, which provides a federal reinsurance backstop, behind the protection built into our property and casualty reinsurance treaties, for terrorism losses covered under the Terrorism Risk Insurance Program Reauthorization Act (“TRIPRA”). For further information about TRIPRA, see Item 1A. “Risk Factors.” of this Form 10-K.

•Flood Reinsurance, for which all of the premiums and losses related to our participation in the WYO (for which we also receive a servicing fee) are 100% ceded to the federal government.

Property Reinsurance

Property Catastrophe Reinsurance Program

Our 2024 property catastrophe reinsurance program includes an excess of loss treaty and an indemnity reinsurance agreement with a special purpose insurer that issued a catastrophe bond (discussed more fully below). This program provides coverage of

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$1.1 billion in excess of a $100 million retention. Compared to our expiring program, we extended the exhaustion limit by $290 million and increased our retention by $40 million to respond to our growing property portfolio. In addition, we eliminated co-participations throughout the program. The overall net purchased limits increased to $1.1 billion, from $810 million in the expiring treaty.

We renewed our property catastrophe treaty, which covers our standard market and E&S business, effective January 1, 2024. The highest layer of the treaty provides 35% coverage of the $500 million in excess of $700 million layer. The property catastrophe treaty excludes coverage for communicable disease but retains (i) coverage for strike, riot, civil unrest, severe convective storms, and other traditionally-covered property perils, (ii) coverage for conventional terrorism losses in most geographic areas, and (iii) limited coverage for cybersecurity risks.

To provide additional, fully collateralized coverage at the top end of our property catastrophe reinsurance program, we secured property catastrophe protection through a per occurrence excess of loss indemnity reinsurance agreement effective December 9, 2023, with High Point Re Ltd. ("High Point Re"), an independent Bermuda special purpose insurer. The reinsurance agreement meets the accounting guidance requirements to be accounted for as reinsurance. In connection with the reinsurance agreement, High Point Re issued Series 2023-1, Class A Principal-at-Risk Variable Rates Notes to unrelated investors totaling $325 million, consistent with the coverage provided under the reinsurance agreement. The proceeds were deposited in a reinsurance trust account. The reinsurance agreement provides us with coverage of up to $325 million for the three-year period from December 9, 2023, through December 31, 2026, for property catastrophe losses from named storms, earthquakes, severe thunderstorms, winter storms, wildfires, meteorite impacts, and volcanic eruptions in all states except California, Florida, Texas, and Louisiana. The reinsurance agreement's attachment point and exhaustion limit may be reset annually to adjust the expected loss of the layer within a predetermined range. For the 2024 treaty year, this reinsurance agreement provides us with coverage for 65% of losses in the $500 million in excess of $700 million layer. The reinsurance agreement is collateralized, which is provided by High Point Re using proceeds from the issuance of the Series 2023-1 Notes.

Reinsurance agreements have credit risk associated with collecting amounts due from reinsurers. With High Point Re, that risk is reduced because the collateralized reinsurance trust account is funded with money market funds domiciled in the U.S. The money market funds invest solely in cash or high-quality direct obligations of the U.S. government, such as U.S. treasury bills and other short-term securities backed by the U.S. government.

SIGI US Equity

SIGI · 10-K · period ended 2023-12-31

Item 1A. Risk Factors.

Item 1B. Unresolved Staff Comments.

Item 1C. Cybersecurity.

Item 2. Properties.

Item 3. Legal Proceedings.

Item 4. Mine Safety Disclosures.

Item 5. Market For Registrant’s Common Equity, Related Stockholder Matters and Issuer Purchases of Equity Securities.

Item 6. Reserved.

Item 7. Management’s Discussion and Analysis of Financial Condition and Results of Operations.

SIGI US Equity☆

SIGI · 10-K · period ended 2023-12-31

Item 1A. Risk Factors.

Item 1B. Unresolved Staff Comments.

Item 1C. Cybersecurity.

Item 2. Properties.

Item 3. Legal Proceedings.

Item 4. Mine Safety Disclosures.

Item 5. Market For Registrant’s Common Equity, Related Stockholder Matters and Issuer Purchases of Equity Securities.

Item 6. Reserved.

Item 7. Management’s Discussion and Analysis of Financial Condition and Results of Operations.

SIGI US Equity