CSS LLC’s Biogen BIIB Stock Holding History

CSS LLC’s Portfolio BIIB Stock Details BIIB Fund Activity

Bought

Maintained

Sold

Quarter	Market Value	Status	Shares	Change in Stake	Trade Value	Portfolio Weight	Portfolio Position
2026 Q1	$499K	Sell	2,720 -3,360	-55%	-$619K	0.02%	525
2025 Q4	$1.07M	Sell	6,080 -1,670	-22%	-$273K	0.05%	301
2025 Q3	$1.09M	Buy	7,750 +830	+12%	+$112K	0.05%	301
2025 Q2	$869K	Buy	6,920 +3,190	+86%	+$397K	0.04%	371
2025 Q1	$510K	Buy	+3,730	New	+$533K	0.03%	471
2022 Q4	–	Sell	-6,378	Closed	-$1.8M	–	958
2022 Q3	$1.7M	Buy	+6,378	New	+$1.35M	0.08%	248
2022 Q1	–	Sell	-2,800	Closed	-$609K	–	1170
2021 Q4	$672K	Buy	+2,800	New	+$720K	0.02%	554
2021 Q3	–	Sell	-1,832	Closed	-$600K	–	1181
2021 Q2	$634K	Sell	1,832 -9,289	-84%	-$2.81M	0.03%	531
2021 Q1	$3.11M	Sell	11,121 -3,968	-26%	-$1.07M	0.13%	151
2020 Q4	$3.69M	Buy	+15,089	New	+$3.89M	0.14%	122
2020 Q3	–	Sell	-19,196	Closed	-$5.35M	–	794
2020 Q2	$5.14M	Buy	19,196 +18,376	+2,241%	+$5.52M	0.29%	86
2020 Q1	$259K	Buy	+820	New	+$249K	0.02%	389

Other funds holding BIIB

BlackRock New York $5.72T AUM 30.48% 1-Year Est. Return

Primecap Management Pasadena, California $127B AUM 44.11% 1-Year Est. Return

Fidelity Investments Boston, Massachusetts $1.9T AUM 41.92% 1-Year Est. Return

VCM

Vanguard Capital Management Malvern, Pennsylvania $4.04T AUM

State Street Boston, Massachusetts $2.9T AUM 29.55% 1-Year Est. Return

VPM

Vanguard Portfolio Management Malvern, Pennsylvania $1.91T AUM

Geode Capital Management Boston, Massachusetts $1.61T AUM 30.72% 1-Year Est. Return

Wellington Management Group Boston, Massachusetts $535B AUM 26.23% 1-Year Est. Return

Morgan Stanley New York $1.66T AUM 25.57% 1-Year Est. Return

JP Morgan Chase New York $1.56T AUM 27.86% 1-Year Est. Return

CSS LLC's BIIB Position: Q1 2026 in Review

CSS LLC reduced its Biogen (BIIB) stake by 55% in Q1 2026, selling an estimated $619K and leaving 2,720 shares worth $499K. The position accounts for 0.02% of the portfolio, ranked #525.

CSS LLC first reported a position in BIIB in Q1 2020 and has held it in 12 quarters since. The position peaked at $5.14M in Q2 2020. 1,002 funds tracked by Wall St. Rank hold BIIB as of Q1 2026.

CSS LLC held 2,720 shares of Biogen worth $499K as of Q1 2026.
CSS LLC sold 3,360 Biogen shares in Q1 2026, an estimated $619K.
Biogen made up 0.02% of CSS LLC's portfolio in Q1 2026, its #525 holding.
CSS LLC first reported a position in Biogen in Q1 2020 and has held it in 12 quarters since.
CSS LLC's Biogen position peaked at $5.14M in Q2 2020.
1,002 funds tracked by Wall St. Rank held Biogen as of Q1 2026.

Based on CSS LLC's 13F filing for Q1 2026, filed 15 May 2026.