SL
UPB

Siren LLC’s Upstream Bio Inc UPB Stock Holding History

Siren LLC’s Portfolio UPB Stock Details UPB Fund Activity
Bought
Maintained
Sold
Quarter Market Value Status Shares Change in
Stake 		Trade Value Portfolio Weight Portfolio Position
2026
Q1 		– Sell
-588,450
Closed -$16M – 129
2025
Q4 		$16M Sell
588,450
-200,000
-25% -$4.98M 0.48% 43
2025
Q3 		$14.8M Hold
788,450
– – 0.58% 41
2025
Q2 		$8.66M Hold
788,450
– – 0.45% 46
2025
Q1 		$4.83M Sell
788,450
-11,550
-1% -$110K 0.27% 55
2024
Q4 		$13.2M Buy
+800,000
New +$17.9M 0.58% 41

Other funds holding UPB

Fidelity Investments
Fidelity Investments Boston, Massachusetts $1.9T AUM 41.92% 1-Year Est. Return
O
OrbiMed New York $5.05B AUM 125.28% 1-Year Est. Return
BlackRock
BlackRock New York $5.72T AUM 30.48% 1-Year Est. Return
DC
Decheng Capital Menlo Park, California $661M AUM 299.97% 1-Year Est. Return
ES
Enavate Sciences Menlo Park, California $352M AUM 220.14% 1-Year Est. Return
VCM
Vanguard Capital Management Malvern, Pennsylvania $4.04T AUM
YIH
Y-Intercept (HK) Hong Kong $5.05B AUM 17.89% 1-Year Est. Return
Federated Hermes
Federated Hermes Pittsburgh, Pennsylvania $61.5B AUM 30.7% 1-Year Est. Return
Geode Capital Management
Geode Capital Management Boston, Massachusetts $1.61T AUM 30.72% 1-Year Est. Return
Millennium Management
Millennium Management New York $240B AUM 35.51% 1-Year Est. Return

Siren LLC's UPB Position: Q1 2026 in Review

Siren LLC sold out of Upstream Bio Inc (UPB) in Q1 2026, closing a stake of 588,450 shares — an estimated $16M sold.

Siren LLC first reported a position in UPB in Q4 2024 and held it in 5 quarters. The position peaked at $16M in Q4 2025. 140 funds tracked by Wall St. Rank hold UPB as of Q1 2026.

  • Siren LLC reported no remaining Upstream Bio Inc position as of Q1 2026 after selling out during the quarter.
  • Siren LLC sold 588,450 Upstream Bio Inc shares in Q1 2026, an estimated $16M.
  • Siren LLC first reported a position in Upstream Bio Inc in Q4 2024 and held it in 5 quarters.
  • Siren LLC's Upstream Bio Inc position peaked at $16M in Q4 2025.
  • 140 funds tracked by Wall St. Rank held Upstream Bio Inc as of Q1 2026.

Based on Siren LLC's 13F filing for Q1 2026, filed 14 May 2026.