EcoR1 Capital, LLC holds a concentrated book of 29 stocks worth $2.3B as of Q1 2026 (disclosed May 15, 2026, a ~45-day 13F lag). This quarter they opened Aktis Oncology Inc and trimmed Xencor Inc. Their largest long position is Zymeworks Inc at 25% of the equity book. They also disclosed $16.3M in call options (bullish), shown separately below and excluded from the equity book.
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Use Arkolith to show EcoR1 Capital, LLC's latest holdings, largest changes, and filing provenance.
Top-heavy: concentrated book
Share of the disclosed book in its largest positions. A higher top-5 share means a more concentrated, higher-conviction portfolio.
100% mapped to company sectors
Direct operating-company sectors from our SIC-based security master. ETF/fund and unclassified holdings stay visible separately; this is not ETF look-through exposure.
Estimated $ traded · quarter-end prices, no cost basis
Bars show each stock's share of the portfolio. Click a row for its position history.
| # | Security | Value | Shares | % Port | Last move | History |
|---|---|---|---|---|---|---|
| 1 | Zymeworks Inc COM | $575.2M | 22.97M | 24.6% | —Held | |
| 2 | Anaptysbio Inc COM | $437.0M | 7.88M | 18.7% | —Held | |
| 3 | Jazz Pharmaceuticals PLC SHS USD | $322.6M | 1.71M | 13.8% | —Held | |
| 4 | Centessa Pharmaceuticals PLC SPONSORED ADS | $238.3M | 6.00M | 10.2% | ▲+93% Added · +2.9M sh | |
| 5 | Crinetics Pharmaceuticals In COM | $155.7M | 4.29M | 6.7% | —Held | |
| 6 | Aktis Oncology Inc COM ADDED | $86.3M | 4.82M | 3.7% | ▲New New position | |
| 7 | Oric Pharmaceuticals Inc COM | $85.2M | 6.73M | 3.6% | —Held | |
| 8 | CG Oncology Inc COM | $74.6M | 1.10M | 3.2% | ▲+43% Added · +330K sh | |
| 9 | Crispr Therapeutics AG NAMEN AKT | $66.1M | 1.39M | 2.8% | —Held | |
| 10 | Eton Pharmaceuticals Inc COM | $53.6M | 2.17M | 2.3% | ▲+7.0% Added · +141K sh | |
| 11 | Galapagos NV SPON ADR | $50.0M | 1.67M | 2.1% | —Held | |
| 12 | Xencor Inc COM | $26.3M | 2.18M | 1.1% | ▼−33% Reduced · −1.1M sh | |
| 13 | Neurogene Inc COM | $25.6M | 1.27M | 1.1% | —Held | |
| 14 | Bridgebio Oncology Therapeut COM NEW | $25.3M | 2.82M | 1.1% | —Held | |
| 15 | MBX Biosciences Inc COM | $23.2M | 777.0K | 1.0% | ▼−63% Reduced · −1.3M sh | |
| 16 | Relay Therapeutics Inc COM | $19.0M | 1.90M | 0.8% | ▲New New position | |
| 17 | Zenas Biopharma Inc COM | $15.4M | 789.5K | 0.7% | —Held | |
| 18 | Erasca Inc COM | $14.6M | 900.0K | 0.6% | ▲New New position | |
| 19 | Eikon Therapeutics Inc COM ADDED | $7.8M | 732.6K | 0.3% | ▲New New position | |
| 20 | Replimune Group Inc COM | $7.7M | 1.00M | 0.3% | ▲New New position | |
| 21 | Zura Bio Ltd CLASS A ORD SHS | $7.0M | 1.18M | 0.3% | ▲New New position | |
| 22 | Phathom Pharmaceuticals Inc COM | $6.9M | 625.0K | 0.3% | ▲New New position | |
| 23 | Mereo Biopharma Group PLC SPON ADS | $4.4M | 13.37M | 0.2% | ▲+70% Added · +5.5M sh | |
| 24 | Stoke Therapeutics Inc COM | $3.3M | 100.0K | 0.1% | ▲New New position | |
| 25 | Prelude Therapeutics Inc COM | $3.2M | 947.0K | 0.1% | ▲New New position | |
| 26 | Ibio Inc COM NEW | $3.0M | 1.58M | 0.1% | ▼−29% Reduced · −645K sh | |
| 27 | Helix Acquisition Corp III Usd CL A ORD SHS ADDED | $2.0M | 200.0K | 0.1% | ▲New New position | |
| 28 | Atara Biotherapeutics Inc COM NEW | $471K | 99.6K | 0.0% | ▼−83% Reduced · −474K sh | |
| 29 | Surrozen Inc *W EXP 08/01/203 | $129K | 4.4K | 0.0% | —Held |
Put / call positions from the 13F — totals include every disclosed option leg
| Type | Underlying | Notional value | Underlying shares |
|---|---|---|---|
| CALL · bullish | CENTESSA PHARMACEUTICALS-ADRCNTA | $16.3M | 411K |
13F filers disclose option positions at the market value of the underlying the contracts reference, not the premium paid. A put is a bearish bet (it gains if the stock falls); a call is bullish. “Underlying shares” is the share count the contracts control, not a share holding. These legs are excluded from the equity book, weighting, concentration and sector figures above.
As-of date vs the date the SEC received each filing
| Quarter | As of | Filed | Positions | Value | Form |
|---|---|---|---|---|---|
| Q1 2026 | Mar 31, 2026 | May 15, 2026 | 30 | $2.4B | 13F-HR |
| Q4 2025 | Dec 31, 2025 | Feb 17, 2026 | 30 | $2.2B | 13F-HR |
| Q3 2025 | Sep 30, 2025 | Nov 14, 2025 | 30 | $2.1B | 13F-HR |
| Q2 2025 | Jun 30, 2025 | Aug 14, 2025 | 37 | $1.7B | 13F-HR |
| Q1 2025 | Mar 31, 2025 | May 15, 2025 | 46 | $1.7B | 13F-HR |
| Q4 2024 | Dec 31, 2024 | Feb 14, 2025 | 59 | $2.6B | 13F-HR |
| Q3 2024 | Sep 30, 2024 | Nov 14, 2024 | 64 | $2.9B | 13F-HR |
| Q2 2024 | Jun 30, 2024 | Aug 14, 2024 | 55 | $3.3B | 13F-HR |
| Q1 2024 | Mar 31, 2024 | May 15, 2024 | 59 | $4.0B | 13F-HR |
| Q4 2023 | Dec 31, 2023 | Feb 14, 2024 | 51 | $3.9B | 13F-HR |
| Q3 2023 | Sep 30, 2023 | Nov 14, 2023 | 51 | $3.0B | 13F-HR |
| Q2 2023 | Jun 30, 2023 | Aug 14, 2023 | 53 | $4.1B | 13F-HR |
| Q1 2023 | Mar 31, 2023 | May 15, 2023 | 58 | $3.1B | 13F-HR |
| Q4 2022 | Dec 31, 2022 | Feb 14, 2023 | 66 | $3.3B | 13F-HR |
| Q3 2022 | Sep 30, 2022 | Nov 14, 2022 | 76 | $3.4B | 13F-HR |
| Q2 2022 | Jun 30, 2022 | Aug 15, 2022 | 80 | $2.9B | 13F-HR |
| Q1 2022 | Mar 31, 2022 | May 16, 2022 | 87 | $3.2B | 13F-HR |
| Q4 2021 | Dec 31, 2021 | Feb 14, 2022 | 76 | $3.1B | 13F-HR |
| Q3 2021 | Sep 30, 2021 | Nov 22, 2021 | 71 | $2.9B | 13F-HR/A |
| Q2 2021 | Jun 30, 2021 | Aug 16, 2021 | 72 | $2.7B | 13F-HR |
| Q1 2021 | Mar 31, 2021 | May 17, 2021 | 71 | $2.3B | 13F-HR |
| Q4 2020 | Dec 31, 2020 | Feb 16, 2021 | 67 | $1.9B | 13F-HR |
| Q3 2020 | Sep 30, 2020 | Nov 16, 2020 | 50 | $1.4B | 13F-HR |
Holdings from SEC EDGAR 13F-HR filings, updated quarterly ~45 days after quarter-end. Public domain. The book and weighting are long equity only; disclosed put/call options are listed separately and excluded from those totals. Price-derived performance is withheld until the price-source policy and freshness gate are green.