BIIB US Equity

BIOGEN INC.

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Health Care · Biological Products, (No Diagnostic Substances) · CIK 875045 · FYE 1231

$209.23

+3.62 (+1.76%)

USD · as of 2026-07-29 · marketstack

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Institutional ownership· 13F filers holding BIIB · 2026-Q1 methodology → sources →

995 holders

% of shares outstanding held

90.9%

Shares held (13F)

134,255,944

Reporting holders

995

Top holders

largest 100 of 995 · Δ vs 2025-Q4

#	Holder	Shares	Value	% of shares out	Δ QoQ
1	BlackRock, Inc.	15,974,60116.0M	$2.9B	10.82%	ADD 8%
2	PRIMECAP MANAGEMENT CO/CA/	14,757,60714.8M	$2.7B	10.00%	—
3	FMR LLC	12,807,54112.8M	$2.3B	8.68%	ADD 36%
4	VANGUARD CAPITAL MANAGEMENT LLC	9,537,4179.5M	$1.7B	6.46%	NEW†
5	STATE STREET CORP	7,167,9227.2M	$1.3B	4.86%	—
6	VANGUARD PORTFOLIO MANAGEMENT LLC	6,531,7276.5M	$1.2B	4.42%	NEW†
7	GEODE CAPITAL MANAGEMENT, LLC	4,342,6024.3M	$793M	2.94%	ADD 3%
8	WELLINGTON MANAGEMENT GROUP LLP	2,961,6413.0M	$543M	2.01%	TRIM -17%
9	MORGAN STANLEY	2,170,9402.2M	$398M	1.47%	TRIM -7%
10	JPMORGAN CHASE & CO	2,016,0092.0M	$378M	1.37%	ADD 9%
11	AQR CAPITAL MANAGEMENT LLC	1,923,5571.9M	$346M	1.30%	ADD 26%
12	Invesco Ltd.	1,745,2551.7M	$320M	1.18%	ADD 5%
13	Boston Partners	1,700,0781.7M	$312M	1.15%	—
14	NORTHERN TRUST CORP	1,446,5791.4M	$265M	0.98%	—
15	UBS AM, a distinct business unit of UBS ASSET MANAGEMENT AMERICAS LLC	1,377,5681.4M	$253M	0.93%	—
16	Legal & General Group Plc	1,349,8321.3M	$247M	0.91%	TRIM -8%
17	T. Rowe Price Investment Management, Inc.	1,160,9891.2M	$213M	0.79%	TRIM -40%
18	BANK OF AMERICA CORP /DE/	1,156,3691.2M	$212M	0.78%	ADD 2%
19	CHARLES SCHWAB INVESTMENT MANAGEMENT INC	1,149,3941.1M	$211M	0.78%	—
20	VAN ECK ASSOCIATES CORP	1,079,8611.1M	$198M	0.73%	—
21	DIMENSIONAL FUND ADVISORS LP	1,079,1191.1M	$198M	0.73%	ADD 12%
22	DEUTSCHE BANK AG\	1,063,8281.1M	$195M	0.72%	ADD 12%
23	GOLDMAN SACHS GROUP INC	1,051,0941.1M	$193M	0.71%	TRIM -4%
24	Pictet Asset Management Holding SA	913,328913,328	$168M	0.62%	TRIM -4%
25	VANGUARD FIDUCIARY TRUST CO	825,531825,531	$151M	0.56%	NEW
26	Point72 Asset Management, L.P.	809,617809,617	$148M	0.55%	TRIM -71%
27	Alyeska Investment Group, L.P.	805,050805,050	$148M	0.55%	TRIM -21%
28	Amundi	790,827790,827	$145M	0.54%	ADD 38%
29	Bank of New York Mellon Corp	788,523788,523	$145M	0.53%	TRIM -3%
30	Robeco Institutional Asset Management B.V.	763,174763,174	$140M	0.52%	ADD 25%
31	FRED ALGER MANAGEMENT, LLC	733,194733,194	$134M	0.50%	TRIM -8%
32	MASSACHUSETTS FINANCIAL SERVICES CO /MA/	720,629720,629	$134M	0.49%	—
33	Employees Provident Fund Board	704,196704,196	$129M	0.48%	—
34	FIRST TRUST ADVISORS LP	673,958673,958	$124M	0.46%	ADD 19%
35	PRICE T ROWE ASSOCIATES INC /MD/	672,427672,427	$123M	0.46%	TRIM -15%
36	Balyasny Asset Management L.P.	650,046650,046	$119M	0.44%	ADD 7%
37	AustralianSuper Pty Ltd	616,193616,193	$113M	0.42%	ADD 29%
38	Artemis Investment Management LLP	571,571571,571	$105M	0.39%	ADD 152%
39	BARCLAYS PLC	551,474551,474	$101M	0.37%	TRIM -58%
40	ROYAL BANK OF CANADA	531,377531,377	$97M	0.36%	—
41	UBS Group AG	523,450523,450	$96M	0.35%	TRIM -18%
42	Zurcher Kantonalbank (Zurich Cantonalbank)	522,155522,155	$96M	0.35%	ADD 15%
43	Caisse de depot et placement du Quebec	518,694518,694	$95M	0.35%	TRIM -12%
44	CITIGROUP INC	500,507500,507	$92M	0.34%	TRIM -13%
45	BNP PARIBAS FINANCIAL MARKETS	471,068471,068	$86M	0.32%	TRIM -7%
46	HSBC HOLDINGS PLC	463,652463,652	$85M	0.31%	TRIM -54%
47	Swiss National Bank	430,600430,600	$79M	0.29%	ADD 7%
48	National Pension Service	401,667401,667	$74M	0.27%	ADD 40%
49	Candriam S.C.A.	381,768381,768	$70M	0.26%	ADD 16%
50	Patient Capital Management, LLC	379,741379,741	$70M	0.26%	TRIM -34%
51	Nuveen, LLC	358,838358,838	$66M	0.24%	TRIM -4%
52	Sumitomo Mitsui Trust Group, Inc.	356,291356,291	$65M	0.24%	TRIM -4%
53	Vanguard Global Advisers, LLC	343,768343,768	$63M	0.23%	NEW
54	California Public Employees Retirement System	340,903340,903	$62M	0.23%	ADD 3%
55	Mitsubishi UFJ Asset Management Co., Ltd.	334,413334,413	$61M	0.23%	ADD 5%
56	LSV ASSET MANAGEMENT	333,739333,739	$61M	0.23%	ADD 5%
57	ADAGE CAPITAL PARTNERS GP, L.L.C.	333,457333,457	$61M	0.23%	ADD 13%
58	VICTORY CAPITAL MANAGEMENT INC	320,785320,785	$59M	0.22%	ADD 30%
59	Man Group plc	318,745318,745	$58M	0.22%	TRIM -6%
60	FIL Ltd	318,056318,056	$58M	0.22%	—
61	Fisher Asset Management, LLC	312,618312,618	$57M	0.21%	ADD 7%
62	Gotham Asset Management, LLC	298,437298,437	$55M	0.20%	ADD 8%
63	Swedbank AB	289,840289,840	$53M	0.20%	ADD 25%
64	CAUSEWAY CAPITAL MANAGEMENT LLC	280,783280,783	$51M	0.19%	TRIM -46%
65	RHUMBLINE ADVISERS	275,438275,438	$50M	0.19%	—
66	AEGON ASSET MANAGEMENT UK Plc	258,735258,735	$47M	0.18%	—
67	VANGUARD ASSET MANAGEMENT, Ltd	249,778249,778	$46M	0.17%	NEW
68	ACADIAN ASSET MANAGEMENT LLC	248,489248,489	$46M	0.17%	ADD 33%
69	THOMPSON SIEGEL & WALMSLEY LLC	248,343248,343	$46M	0.17%	ADD 9%
70	KBC Group NV	234,692234,692	$43M	0.16%	ADD 340%
71	MARSHALL WACE, LLP	229,879229,879	$42M	0.16%	TRIM -40%
72	Sofinnova Investments, Inc.	229,521229,521	$42M	0.16%	NEW
73	CALIFORNIA STATE TEACHERS RETIREMENT SYSTEM	220,687220,687	$40M	0.15%	TRIM -3%
74	BNP PARIBAS ASSET MANAGEMENT Holding S.A.	215,436215,436	$40M	0.15%	TRIM -12%
75	Qube Research & Technologies Ltd	212,921212,921	$39M	0.14%	NEW
76	ALLIANCEBERNSTEIN L.P.	212,897212,897	$37M	0.14%	ADD 16%
77	RENAISSANCE TECHNOLOGIES LLC	203,396203,396	$37M	0.14%	TRIM -49%
78	Hudson Bay Capital Management LP	201,367201,367	$37M	0.14%	TRIM -9%
79	Logos Global Management LP	200,000200,000	$37M	0.14%	—
80	KLP KAPITALFORVALTNING AS	199,177199,177	$37M	0.13%	ADD 4%
81	SG Americas Securities, LLC	195,668195,668	$36M	0.13%	ADD 6%
82	PRINCIPAL FINANCIAL GROUP INC	187,059187,059	$34M	0.13%	—
83	Allianz Asset Management GmbH	178,049178,049	$33M	0.12%	TRIM -28%
84	PRUDENTIAL FINANCIAL INC	163,887163,887	$30M	0.11%	TRIM -54%
85	IEQ CAPITAL, LLC	152,076152,076	$28M	0.10%	ADD 9%
86	ExodusPoint Capital Management, LP	151,993151,993	$28M	0.10%	NEW
87	Aberdeen Group plc	151,144151,144	$28M	0.10%	ADD 8%
88	LETKO, BROSSEAU & ASSOCIATES INC	150,865150,865	$28M	0.10%	ADD 16%
89	FRANKLIN RESOURCES INC	144,448144,448	$26M	0.10%	ADD 2%
90	PANAGORA ASSET MANAGEMENT INC	142,065142,065	$26M	0.10%	ADD 4335%
91	O'SHAUGHNESSY ASSET MANAGEMENT, LLC	141,324141,324	$26M	0.10%	ADD 28%
92	Palo Alto Investors LP	140,719140,719	$26M	0.10%	TRIM -23%
93	SUSQUEHANNA INTERNATIONAL GROUP, LLP	140,299140,299	$26M	0.10%	TRIM -79%
94	CITADEL ADVISORS LLC	138,093138,093	$25M	0.09%	ADD 242%
95	Russell Investments Group, Ltd.	135,841135,841	$25M	0.09%	ADD 14%
96	AMERIPRISE FINANCIAL INC	132,603132,603	$24M	0.09%	—
97	Eurizon Capital SGR S.p.A.	129,204129,204	$24M	0.09%	—
98	TD Asset Management Inc	127,268127,268	$23M	0.09%	TRIM -6%
99	WELLS FARGO & COMPANY/MN	127,134127,134	$23M	0.09%	ADD 7%
100	STATE BOARD OF ADMINISTRATION OF FLORIDA RETIREMENT SYSTEM	124,212124,212	$23M	0.08%	—

† a filer this large appearing as NEW usually reflects a renamed or succeeded filing entity (the old name stops filing the same quarter) — not a brand-new position.

Rows rank by the value each filer reported — 13F filers price their own positions, so a holder with fewer shares can rank just above one with more.

Holder trends· top 15 holders · shares held over 6 quarters

green added · red trimmed

Holder

2024-Q4

2025-Q1

2025-Q2

2025-Q3

2025-Q4

2026-Q1

Latest value

BlackRock, Inc.

15.5M

15.2M

13.6M

14.8M

16.0M

$2.9B

PRIMECAP MANAGEMENT CO/CA/

16.0M

15.9M

15.8M

15.0M

14.8M

$2.7B

FMR LLC

758K

1.3M

1.7M

1.3M

9.4M

12.8M

$2.3B

VANGUARD CAPITAL MANAGEMENT LLC

—

9.5M

$1.7B

STATE STREET CORP

7.4M

7.5M

7.3M

7.2M

$1.3B

VANGUARD PORTFOLIO MANAGEMENT LLC

—

6.5M

$1.2B

GEODE CAPITAL MANAGEMENT, LLC

3.7M

3.8M

3.9M

4.1M

4.2M

4.3M

$793M

WELLINGTON MANAGEMENT GROUP LLP

4.9M

4.7M

4.8M

4.2M

3.6M

3.0M

$543M

MORGAN STANLEY

1.8M

2.0M

2.3M

2.2M

$398M

JPMORGAN CHASE & CO

2.1M

1.5M

1.0M

2.5M

1.9M

2.0M

$378M

AQR CAPITAL MANAGEMENT LLC

540K

1.4M

1.8M

1.5M

1.9M

$346M

Invesco Ltd.

2.1M

2.3M

2.4M

1.7M

$320M

Boston Partners

—

1.7M

$312M

NORTHERN TRUST CORP

1.6M

1.5M

1.4M

$265M

UBS AM, a distinct business unit of UBS ASSET MANAGEMENT AMERICAS LLC

1.5M

1.7M

1.4M

$253M

Shares reported each quarter by the largest current holders. Green = added vs the prior filing, red = trimmed, grey = roughly held; a dash is a quarter with no 13F on file (a gap is skipped, not read as an exit). 13F is filed up to 45 days after quarter-end. Up to 40 quarters (10 years) available — use the selector above.

Institutional footprint by quarter

Line breaks are honest gaps — quarters with no 13F record, or a suppressed % — never interpolated. % of shares outstanding uses today's share count for every quarter (the only count stored).

Quarter	Holders	Shares held	% shares out	Value held
2026-Q1	995	134,255,944	90.9%	$24.6B
2025-Q4

Short interest has its own tab now — open SI →

Source: SEC Form 13F — every institution manager (≥ $100M in 13F securities) reporting a long US-listed position, across ~10,250 filers over 10 years of history. 13F is long-only, US-listed, filed up to 45 days after quarter-end.

Activists & large holders· Schedule 13D/G beneficial owners · BIIB

Large holders — 13G, passive (top 5 of 6 by % of class)

Holder	% of class	Type	As of
FMR LLC	11.3%	QII	2026-05-29	SEC →
PRIMECAP MANAGEMENT CO/CA/	10.2%	QII	2025-09-30	SEC →
BlackRock, Inc.	8.5%	QII	2025-03-31	SEC →
VANGUARD CAPITAL MANAGEMENT LLC	7.48%	QII	2026-03-31	SEC →
STATE STREET CORP	5%	QII	2025-09-30

Institutional ownership· 13F filers holding BIIB · 2026-Q1 methodology → sources →

995 holders

% of shares outstanding held

90.9%

Shares held (13F)

134,255,944

Reporting holders

995

Top holders

largest 100 of 995 · Δ vs 2025-Q4

#	Holder	Shares	Value	% of shares out	Δ QoQ
1	BlackRock, Inc.	15,974,60116.0M	$2.9B	10.82%	ADD 8%
2	PRIMECAP MANAGEMENT CO/CA/	14,757,60714.8M	$2.7B	10.00%	—
3	FMR LLC	12,807,54112.8M	$2.3B	8.68%	ADD 36%
4	VANGUARD CAPITAL MANAGEMENT LLC	9,537,4179.5M	$1.7B	6.46%	NEW†
5	STATE STREET CORP	7,167,9227.2M	$1.3B	4.86%	—
6	VANGUARD PORTFOLIO MANAGEMENT LLC	6,531,7276.5M	$1.2B	4.42%	NEW†
7	GEODE CAPITAL MANAGEMENT, LLC	4,342,6024.3M	$793M	2.94%	ADD 3%
8	WELLINGTON MANAGEMENT GROUP LLP	2,961,6413.0M	$543M	2.01%	TRIM -17%
9	MORGAN STANLEY	2,170,9402.2M	$398M	1.47%	TRIM -7%
10	JPMORGAN CHASE & CO	2,016,0092.0M	$378M	1.37%	ADD 9%
11	AQR CAPITAL MANAGEMENT LLC	1,923,5571.9M	$346M	1.30%	ADD 26%
12	Invesco Ltd.	1,745,2551.7M	$320M	1.18%	ADD 5%
13	Boston Partners	1,700,0781.7M	$312M	1.15%	—
14	NORTHERN TRUST CORP	1,446,5791.4M	$265M	0.98%	—
15	UBS AM, a distinct business unit of UBS ASSET MANAGEMENT AMERICAS LLC	1,377,5681.4M	$253M	0.93%	—
16	Legal & General Group Plc	1,349,8321.3M	$247M	0.91%	TRIM -8%
17	T. Rowe Price Investment Management, Inc.	1,160,9891.2M	$213M	0.79%	TRIM -40%
18	BANK OF AMERICA CORP /DE/	1,156,3691.2M	$212M	0.78%	ADD 2%
19	CHARLES SCHWAB INVESTMENT MANAGEMENT INC	1,149,3941.1M	$211M	0.78%	—
20	VAN ECK ASSOCIATES CORP	1,079,8611.1M	$198M	0.73%	—
21	DIMENSIONAL FUND ADVISORS LP	1,079,1191.1M	$198M	0.73%	ADD 12%
22	DEUTSCHE BANK AG\	1,063,8281.1M	$195M	0.72%	ADD 12%
23	GOLDMAN SACHS GROUP INC	1,051,0941.1M	$193M	0.71%	TRIM -4%
24	Pictet Asset Management Holding SA	913,328913,328	$168M	0.62%	TRIM -4%
25	VANGUARD FIDUCIARY TRUST CO	825,531825,531	$151M	0.56%	NEW
26	Point72 Asset Management, L.P.	809,617809,617	$148M	0.55%	TRIM -71%
27	Alyeska Investment Group, L.P.	805,050805,050	$148M	0.55%	TRIM -21%
28	Amundi	790,827790,827	$145M	0.54%	ADD 38%
29	Bank of New York Mellon Corp	788,523788,523	$145M	0.53%	TRIM -3%
30	Robeco Institutional Asset Management B.V.	763,174763,174	$140M	0.52%	ADD 25%
31	FRED ALGER MANAGEMENT, LLC	733,194733,194	$134M	0.50%	TRIM -8%
32	MASSACHUSETTS FINANCIAL SERVICES CO /MA/	720,629720,629	$134M	0.49%	—
33	Employees Provident Fund Board	704,196704,196	$129M	0.48%	—
34	FIRST TRUST ADVISORS LP	673,958673,958	$124M	0.46%	ADD 19%
35	PRICE T ROWE ASSOCIATES INC /MD/	672,427672,427	$123M	0.46%	TRIM -15%
36	Balyasny Asset Management L.P.	650,046650,046	$119M	0.44%	ADD 7%
37	AustralianSuper Pty Ltd	616,193616,193	$113M	0.42%	ADD 29%
38	Artemis Investment Management LLP	571,571571,571	$105M	0.39%	ADD 152%
39	BARCLAYS PLC	551,474551,474	$101M	0.37%	TRIM -58%
40	ROYAL BANK OF CANADA	531,377531,377	$97M	0.36%	—
41	UBS Group AG	523,450523,450	$96M	0.35%	TRIM -18%
42	Zurcher Kantonalbank (Zurich Cantonalbank)	522,155522,155	$96M	0.35%	ADD 15%
43	Caisse de depot et placement du Quebec	518,694518,694	$95M	0.35%	TRIM -12%
44	CITIGROUP INC	500,507500,507	$92M	0.34%	TRIM -13%
45	BNP PARIBAS FINANCIAL MARKETS	471,068471,068	$86M	0.32%	TRIM -7%
46	HSBC HOLDINGS PLC	463,652463,652	$85M	0.31%	TRIM -54%
47	Swiss National Bank	430,600430,600	$79M	0.29%	ADD 7%
48	National Pension Service	401,667401,667	$74M	0.27%	ADD 40%
49	Candriam S.C.A.	381,768381,768	$70M	0.26%	ADD 16%
50	Patient Capital Management, LLC	379,741379,741	$70M	0.26%	TRIM -34%
51	Nuveen, LLC	358,838358,838	$66M	0.24%	TRIM -4%
52	Sumitomo Mitsui Trust Group, Inc.	356,291356,291	$65M	0.24%	TRIM -4%
53	Vanguard Global Advisers, LLC	343,768343,768	$63M	0.23%	NEW
54	California Public Employees Retirement System	340,903340,903	$62M	0.23%	ADD 3%
55	Mitsubishi UFJ Asset Management Co., Ltd.	334,413334,413	$61M	0.23%	ADD 5%
56	LSV ASSET MANAGEMENT	333,739333,739	$61M	0.23%	ADD 5%
57	ADAGE CAPITAL PARTNERS GP, L.L.C.	333,457333,457	$61M	0.23%	ADD 13%
58	VICTORY CAPITAL MANAGEMENT INC	320,785320,785	$59M	0.22%	ADD 30%
59	Man Group plc	318,745318,745	$58M	0.22%	TRIM -6%
60	FIL Ltd	318,056318,056	$58M	0.22%	—
61	Fisher Asset Management, LLC	312,618312,618	$57M	0.21%	ADD 7%
62	Gotham Asset Management, LLC	298,437298,437	$55M	0.20%	ADD 8%
63	Swedbank AB	289,840289,840	$53M	0.20%	ADD 25%
64	CAUSEWAY CAPITAL MANAGEMENT LLC	280,783280,783	$51M	0.19%	TRIM -46%
65	RHUMBLINE ADVISERS	275,438275,438	$50M	0.19%	—
66	AEGON ASSET MANAGEMENT UK Plc	258,735258,735	$47M	0.18%	—
67	VANGUARD ASSET MANAGEMENT, Ltd	249,778249,778	$46M	0.17%	NEW
68	ACADIAN ASSET MANAGEMENT LLC	248,489248,489	$46M	0.17%	ADD 33%
69	THOMPSON SIEGEL & WALMSLEY LLC	248,343248,343	$46M	0.17%	ADD 9%
70	KBC Group NV	234,692234,692	$43M	0.16%	ADD 340%
71	MARSHALL WACE, LLP	229,879229,879	$42M	0.16%	TRIM -40%
72	Sofinnova Investments, Inc.	229,521229,521	$42M	0.16%	NEW
73	CALIFORNIA STATE TEACHERS RETIREMENT SYSTEM	220,687220,687	$40M	0.15%	TRIM -3%
74	BNP PARIBAS ASSET MANAGEMENT Holding S.A.	215,436215,436	$40M	0.15%	TRIM -12%
75	Qube Research & Technologies Ltd	212,921212,921	$39M	0.14%	NEW
76	ALLIANCEBERNSTEIN L.P.	212,897212,897	$37M	0.14%	ADD 16%
77	RENAISSANCE TECHNOLOGIES LLC	203,396203,396	$37M	0.14%	TRIM -49%
78	Hudson Bay Capital Management LP	201,367201,367	$37M	0.14%	TRIM -9%
79	Logos Global Management LP	200,000200,000	$37M	0.14%	—
80	KLP KAPITALFORVALTNING AS	199,177199,177	$37M	0.13%	ADD 4%
81	SG Americas Securities, LLC	195,668195,668	$36M	0.13%	ADD 6%
82	PRINCIPAL FINANCIAL GROUP INC	187,059187,059	$34M	0.13%	—
83	Allianz Asset Management GmbH	178,049178,049	$33M	0.12%	TRIM -28%
84	PRUDENTIAL FINANCIAL INC	163,887163,887	$30M	0.11%	TRIM -54%
85	IEQ CAPITAL, LLC	152,076152,076	$28M	0.10%	ADD 9%
86	ExodusPoint Capital Management, LP	151,993151,993	$28M	0.10%	NEW
87	Aberdeen Group plc	151,144151,144	$28M	0.10%	ADD 8%
88	LETKO, BROSSEAU & ASSOCIATES INC	150,865150,865	$28M	0.10%	ADD 16%
89	FRANKLIN RESOURCES INC	144,448144,448	$26M	0.10%	ADD 2%
90	PANAGORA ASSET MANAGEMENT INC	142,065142,065	$26M	0.10%	ADD 4335%
91	O'SHAUGHNESSY ASSET MANAGEMENT, LLC	141,324141,324	$26M	0.10%	ADD 28%
92	Palo Alto Investors LP	140,719140,719	$26M	0.10%	TRIM -23%
93	SUSQUEHANNA INTERNATIONAL GROUP, LLP	140,299140,299	$26M	0.10%	TRIM -79%
94	CITADEL ADVISORS LLC	138,093138,093	$25M	0.09%	ADD 242%
95	Russell Investments Group, Ltd.	135,841135,841	$25M	0.09%	ADD 14%
96	AMERIPRISE FINANCIAL INC	132,603132,603	$24M	0.09%	—
97	Eurizon Capital SGR S.p.A.	129,204129,204	$24M	0.09%	—
98	TD Asset Management Inc	127,268127,268	$23M	0.09%	TRIM -6%
99	WELLS FARGO & COMPANY/MN	127,134127,134	$23M	0.09%	ADD 7%
100	STATE BOARD OF ADMINISTRATION OF FLORIDA RETIREMENT SYSTEM	124,212124,212	$23M	0.08%	—

† a filer this large appearing as NEW usually reflects a renamed or succeeded filing entity (the old name stops filing the same quarter) — not a brand-new position.

Rows rank by the value each filer reported — 13F filers price their own positions, so a holder with fewer shares can rank just above one with more.

Holder trends· top 15 holders · shares held over 6 quarters

green added · red trimmed

Holder

2024-Q4

2025-Q1

2025-Q2

2025-Q3

2025-Q4

2026-Q1

Latest value

BlackRock, Inc.

15.5M

15.2M

13.6M

14.8M

16.0M

$2.9B

PRIMECAP MANAGEMENT CO/CA/

16.0M

15.9M

15.8M

15.0M

14.8M

$2.7B

FMR LLC

758K

1.3M

1.7M

1.3M

9.4M

12.8M

$2.3B

VANGUARD CAPITAL MANAGEMENT LLC

—

9.5M

$1.7B

STATE STREET CORP

7.4M

7.5M

7.3M

7.2M

$1.3B

VANGUARD PORTFOLIO MANAGEMENT LLC

—

6.5M

$1.2B

GEODE CAPITAL MANAGEMENT, LLC

3.7M

3.8M

3.9M

4.1M

4.2M

4.3M

$793M

WELLINGTON MANAGEMENT GROUP LLP

4.9M

4.7M

4.8M

4.2M

3.6M

3.0M

$543M

MORGAN STANLEY

1.8M

2.0M

2.3M

2.2M

$398M

JPMORGAN CHASE & CO

2.1M

1.5M

1.0M

2.5M

1.9M

2.0M

$378M

AQR CAPITAL MANAGEMENT LLC

540K

1.4M

1.8M

1.5M

1.9M

$346M

Invesco Ltd.

2.1M

2.3M

2.4M

1.7M

$320M

Boston Partners

—

1.7M

$312M

NORTHERN TRUST CORP

1.6M

1.5M

1.4M

$265M

UBS AM, a distinct business unit of UBS ASSET MANAGEMENT AMERICAS LLC

1.5M

1.7M

1.4M

$253M

Institutional footprint by quarter

Line breaks are honest gaps — quarters with no 13F record, or a suppressed % — never interpolated. % of shares outstanding uses today's share count for every quarter (the only count stored).

Quarter	Holders	Shares held	% shares out	Value held
2026-Q1	995	134,255,944	90.9%	$24.6B
2025-Q4

Short interest has its own tab now — open SI →

Activists & large holders· Schedule 13D/G beneficial owners · BIIB

Large holders — 13G, passive (top 5 of 6 by % of class)

Holder	% of class	Type	As of
FMR LLC	11.3%	QII	2026-05-29	SEC →
PRIMECAP MANAGEMENT CO/CA/	10.2%	QII	2025-09-30	SEC →
BlackRock, Inc.	8.5%	QII	2025-03-31	SEC →
VANGUARD CAPITAL MANAGEMENT LLC	7.48%	QII	2026-03-31	SEC →
STATE STREET CORP	5%	QII	2025-09-30

BIIB US Equity☆

Institutional ownership· 13F filers holding BIIB · 2026-Q1 methodology → sources →

Top holders

Holder trends· top 15 holders · shares held over 6 quarters

Institutional footprint by quarter

Activists & large holders· Schedule 13D/G beneficial owners · BIIB

Institutional ownership· 13F filers holding BIIB · 2026-Q1 methodology → sources →

Top holders

Holder trends· top 15 holders · shares held over 6 quarters

Institutional footprint by quarter

Activists & large holders· Schedule 13D/G beneficial owners · BIIB

BIIB US Equity