Julian Baker's Baker Brothers Advisors LP reported total AUM of $15.3B across 20 positions in its Q1 2026 13F filing, disclosing five new biotech initiations including CELC and MIRM. The firm simultaneously exited five positions in full — RARE, TERN, BCRX, Ventyx, and NUVL — while significantly trimming IMCR and BNTX by 68% each.
Top 5 Holdings — Q1 2026
- INCY: $2.9B (16.6%)
- ONC: $2.6B (15.0%)
- INSM: $1.2B (7.0%)
- MDGL: $1.1B (6.4%)
- ACAD: $955M (5.5%)
Q1 2026 Key Portfolio Moves
The portfolio remains anchored by INCY ($2.9B, 16.6%) and ONC ($2.6B, 15.0%), which together account for 31.6% of total AUM. INSM ($1.2B, 7.0%), MDGL ($1.1B, 6.4%), and ACAD ($955M, 5.5%) round out the top five, with the group collectively representing over 40% of the portfolio — underscoring Baker Brothers' hallmark high-conviction, concentrated biotech approach. INSM stands out as a notable conviction builder, with its weighting expanded by 13% quarter-over-quarter.
- CELC: New position — $75M initiated, entered top 7 holdings; Baker's latest high-conviction biotech bet
- MIRM: New position — $41M initiated, establishing fresh exposure to rare cholestatic liver disease
- INSM: Added +13% ($1.2B) — reflects advancing clinical progress in pulmonary nontuberculous mycobacterial infection
- RARE: Full exit — $64M position liquidated entirely, signaling end of investment thesis
- IMCR: Reduced -68% ($22M remaining) — sharp conviction cut, portfolio risk recalibration
- NUVL: Full exit — $14M position closed, part of broader portfolio concentration effort
Among new initiations, CELC represents the largest commitment at $75M. Notably, it simultaneously appears in the top 10 at $904M — suggesting a pre-existing stake was already on the books and that Baker is rapidly building conviction in the name. In contrast, the steep reductions in IMCR (-68%, $22M remaining) and BNTX (-68%, $11M remaining) are best interpreted as a reassessment of pipeline prospects or commercialization outlook for each.
Concentrated Biotech Strategy: Doubling Down on Selectivity
Baker Brothers once again maintained a tight 20-position portfolio this quarter, staying true to its high-concentration strategy centered on oncology and rare diseases. The full exits from RARE, NUVL, BCRX, and two others reflect the firm's disciplined culture of cutting losses swiftly when catalysts fail to materialize or performance disappoints. Meanwhile, the increased allocation to INSM and the sizable initiation of CELC signal continued selective conviction in late-stage clinical or early-commercial pipeline assets. Given the portfolio's persistent concentration, individual clinical events will continue to carry outsized influence on the fund's overall performance.
