EcoR1 Capital, LLC 13F: Quarter-over-Quarter Portfolio Changes
EcoR1 Capital, LLC reported a disclosed portfolio value of approximately $2.0 billion in its latest SEC Form 13F-HR filing for Q2 2026, down 13.8% quarter on quarter. Over the quarter, the fund initiated 9 new positions, bought more shares in 3 holdings, trimmed 4 holdings, and exited 7 positions.
EcoR1 Capital, LLC's top buy was a new stake in First Tracks Biotherapeutics (TRAX) , equal to 3.2% of the disclosed portfolio. Its top sell was Jazz Pharmaceuticals PLC (JAZZ) . The fund exited the position completely after it had accounted for 13.8% of the previous portfolio.
New PositionsQ2 2026
Securities disclosed for the first time in Q2 2026 that were not present in the prior 13F-HR filing.
| Company | Ticker | Initial Portfolio Weight | History |
|---|---|---|---|
| FIRST TRACKS BIOTHERAPEUTICS | TRAX | 3.2% | History → |
| FULCRUM THERAPEUTICS INC | FULC | 1.2% | Holders → |
| LEGEND BIOTECH CORP | LEGN | 1.1% | Holders → |
| AURA BIOSCIENCES INC | AURA | 0.6% | Holders → |
| ODYSSEY THERAPEUTICS INC | ODTX | 0.5% | Holders → |
| PHARVARIS N V | PHVS | 0.4% | Holders → |
| NURIX THERAPEUTICS INC | NRIX | 0.3% | Holders → |
| ELOXX PHARMACEUTICALS INC | ELOX | 0.3% | Holders → |
| AARDVARK THERAPEUTICS INC | AARD | 0.1% | Holders → |
Top BuysQ2 2026
The fund's top buys among existing positions in Q2 2026. Ranked by portfolio-weight impact, with the percentage of additional shares shown separately.
| Company | Ticker | Portfolio Weight Change | More Shares | History |
|---|---|---|---|---|
| ATARA BIOTHERAPEUTICS INC | ATRA | +0.9% | +1458.3% | Holders → |
| STOKE THERAPEUTICS INC | STOK | +1.1% | +635.0% | Holders → |
| CG ONCOLOGY INC | CGON | +2.1% | +35.6% | History → |
Top SellsQ2 2026
The fund's top sells among positions it retained in Q2 2026. Ranked by portfolio-weight impact. Full exits are listed separately.
| Company | Ticker | Portfolio Weight Change | Shares Sold | History |
|---|---|---|---|---|
| MEREO BIOPHARMA GROUP PLC | MREO | -0.2% | 92.5% | Holders → |
| RELAY THERAPEUTICS INC | RLAY | -0.2% | 63.4% | Holders → |
| ERASCA INC | ERAS | -0.3% | 63.3% | Holders → |
| MBX BIOSCIENCES INC | MBX | 0.1% | 50.0% | Holders → |
Full ExitsQ2 2026
Positions present in the prior 13F-HR filing that no longer appear in Q2 2026.
| Company | Ticker | Last-Reported Portfolio Weight |
|---|---|---|
| JAZZ PHARMACEUTICALS PLC | JAZZ | 13.8% |
| CENTESSA PHARMACEUTICALS PLC | CNTA | 10.2% |
| CRINETICS PHARMACEUTICALS, INC. | CRNX | 6.7% |
| XENCOR INC | XNCR | 1.1% |
| REPLIMUNE GROUP, INC. | REPL | 0.3% |
| PRELUDE THERAPEUTICS INC. | PRLD | 0.1% |
| IBIO INC | IBIO | 0.1% |
Net Portfolio Value ChangeQ2 2026
- $2.3BPrior quarter
- $2.0BCurrent quarter
- $-0.3BNet delta
- -13.8%% change
Methodology & FAQ
How EcoR1 Capital, LLC Quarterly Changes Are Computed
All deltas are sourced from sequential SEC Form 13F-HR filings for EcoR1 Capital, LLC: each row joins the most recent filing against the immediately preceding quarterly filing for the same fund. Share-count changes reflect reported trading activity, while portfolio weights can also move because of market price changes. Portfolio weights are normalized to exclude listed options for comparability. A complete description, including how confidential treatment filings are handled, is documented in the Methodology.
What stocks did EcoR1 Capital, LLC buy in Q2 2026?
In Q2 2026, EcoR1 Capital, LLC initiated 9 new positions (FIRST TRACKS BIOTHERAPEUTICS (TRAX), FULCRUM THERAPEUTICS INC (FULC), LEGEND BIOTECH CORP (LEGN), AURA BIOSCIENCES INC (AURA), ODYSSEY THERAPEUTICS INC (ODTX), PHARVARIS N V (PHVS), NURIX THERAPEUTICS INC (NRIX), ELOXX PHARMACEUTICALS INC (ELOX), AARDVARK THERAPEUTICS INC (AARD)); bought more shares of ATARA BIOTHERAPEUTICS INC (ATRA), STOKE THERAPEUTICS INC (STOK), CG ONCOLOGY INC (CGON).
What stocks did EcoR1 Capital, LLC sell in Q2 2026?
In Q2 2026, EcoR1 Capital, LLC fully sold 7 positions (JAZZ PHARMACEUTICALS PLC (JAZZ), CENTESSA PHARMACEUTICALS PLC (CNTA), CRINETICS PHARMACEUTICALS, INC. (CRNX), XENCOR INC (XNCR), REPLIMUNE GROUP, INC. (REPL), PRELUDE THERAPEUTICS INC. (PRLD), IBIO INC (IBIO)); reduced holdings in MEREO BIOPHARMA GROUP PLC (MREO), RELAY THERAPEUTICS INC (RLAY), ERASCA INC (ERAS), MBX BIOSCIENCES INC (MBX).
Which positions did EcoR1 Capital, LLC initiate in Q2 2026?
EcoR1 Capital, LLC established 9 new positions in Q2 2026: FIRST TRACKS BIOTHERAPEUTICS (TRAX, 3.2%), FULCRUM THERAPEUTICS INC (FULC, 1.2%), LEGEND BIOTECH CORP (LEGN, 1.1%), AURA BIOSCIENCES INC (AURA, 0.6%), ODYSSEY THERAPEUTICS INC (ODTX, 0.5%), PHARVARIS N V (PHVS, 0.4%), NURIX THERAPEUTICS INC (NRIX, 0.3%), ELOXX PHARMACEUTICALS INC (ELOX, 0.3%), AARDVARK THERAPEUTICS INC (AARD, 0.1%).
Which existing positions saw the largest allocation increases for EcoR1 Capital, LLC in Q2 2026?
Of 3 existing positions with share-count increases in Q2 2026, the largest were: ATARA BIOTHERAPEUTICS INC (ATRA, +0.9% weight, +1458.3% shares), STOKE THERAPEUTICS INC (STOK, +1.1% weight, +635.0% shares), CG ONCOLOGY INC (CGON, +2.1% weight, +35.6% shares).
Which positions did EcoR1 Capital, LLC fully exit in Q2 2026?
EcoR1 Capital, LLC fully exited 7 positions in Q2 2026: JAZZ PHARMACEUTICALS PLC (JAZZ, last-reported weight 13.8%), CENTESSA PHARMACEUTICALS PLC (CNTA, last-reported weight 10.2%), CRINETICS PHARMACEUTICALS, INC. (CRNX, last-reported weight 6.7%), XENCOR INC (XNCR, last-reported weight 1.1%), REPLIMUNE GROUP, INC. (REPL, last-reported weight 0.3%), PRELUDE THERAPEUTICS INC. (PRLD, last-reported weight 0.1%), IBIO INC (IBIO, last-reported weight 0.1%).
Which existing positions saw the largest allocation reductions for EcoR1 Capital, LLC in Q2 2026?
Of 4 existing positions with share-count reductions in Q2 2026, the largest were: MEREO BIOPHARMA GROUP PLC (MREO, -0.2% weight, -92.5% shares), RELAY THERAPEUTICS INC (RLAY, -0.2% weight, -63.4% shares), ERASCA INC (ERAS, -0.3% weight, -63.3% shares), MBX BIOSCIENCES INC (MBX, 0.1% weight, -50.0% shares).
Do quarter-over-quarter 13F allocation changes constitute explicit trading signals?
No. Quarter-over-quarter changes reflect a combination of active trading and market price movement. A weight increase can result from price appreciation alone, without the manager adding shares. Share-count delta is the cleaner indicator of explicit trading activity. All deltas on this page are sourced from sequential SEC Form 13F-HR filings.