Form 4: ALUMIS Director Boosts Stake with Over 500K Shares

James B. Tananbaum, a Director and 10% owner of ALUMIS INC., reported the acquisition of 507,874 shares of common stock across multiple transactions in mid-November 2025.

Summary

• James B. Tananbaum, a Director and 10% owner of ALUMIS INC. (ALMS), acquired a total of 507,874 shares of common stock.
• The acquisitions occurred over several days: 11/17/2025, 11/18/2025, and 11/19/2025.
• Transaction prices ranged from $5.59 to $6.56 per share.
• The shares are held indirectly through various Foresite Capital entities, including Foresite Capital Opportunity Fund V, L.P., Foresite Capital Fund VI, L.P., Foresite Capital Fund V, L.P., Labs Co-Invest V, LLC, Foresite Labs Fund I, L.P., and Foresite Labs Affiliates 2021, LLC.
• Following these transactions, Tananbaum's total indirect beneficial ownership across all reported entities is 15,705,828 shares.
• The transactions were made pursuant to a Rule 10b5-1(c) plan.

Sentiment

Score: 8

Explanation: The significant insider buying by a director and 10% owner, executed under a 10b5-1 plan, strongly suggests confidence in the company's prospects. This is generally a very positive signal for investors.

Positives

• A director and significant owner increasing their stake can signal strong confidence in the company's future prospects.
• The transactions were executed under a Rule 10b5-1(c) plan, indicating a pre-planned investment strategy rather than a reaction to immediate market events.

Future Outlook

The filing does not provide explicit forward-looking statements or guidance, but the insider buying activity may be interpreted as a positive signal regarding the company's future prospects.

Management Comments

• Tananbaum disclaims the existence of a 'group', as defined in Rule 13d-5 of the Securities Exchange Act of 1934, as amended (the 'Exchange Act'), and disclaims beneficial ownership of the shares held by the various Foresite Capital entities, except to the extent of such person's pecuniary interest in such securities.

Industry Context

Insider buying, especially by a director and significant owner, can be a strong indicator of management's confidence in the company's valuation and future performance, potentially signaling a belief that the stock is undervalued or poised for growth. This activity is generally viewed favorably by the market, particularly in sectors like biotechnology or healthcare where ALUMIS INC. likely operates, as it suggests internal conviction despite market volatility or industry-specific challenges.

Comparison to Industry Standards

• Insider buying activity is a common occurrence across industries. However, the scale of this acquisition (over half a million shares) by a director and 10% owner is notable and often interpreted more positively than smaller, routine purchases.
• Compared to other biotech or healthcare companies, significant insider purchases can sometimes precede positive clinical trial results, regulatory approvals, or strategic partnerships, though this filing does not provide such details.
• The use of a Rule 10b5-1 plan is standard practice for insiders to manage stock transactions in compliance with insider trading laws, demonstrating a pre-planned approach rather than opportunistic trading.

Related Party Transactions

• The transactions involve James B. Tananbaum, a director and 10% owner, acquiring shares through various Foresite Capital entities where he holds managing roles. This constitutes a related party transaction in terms of beneficial ownership.

Stakeholder Impact

• Shareholders may view the insider buying as a positive indicator, potentially increasing confidence and demand for the stock.
• Management and employees could experience a boost in morale and reinforced belief in the company's direction.

Next Steps

• Investors will likely monitor future insider transaction reports for ALUMIS INC.
• Market participants may look for further company announcements that could justify this significant insider investment.

Key Dates

Recommendation

The substantial insider buying by James B. Tananbaum, a director and 10% owner, signals strong confidence in ALUMIS INC.'s future. Such significant purchases by an insider, especially under a pre-planned 10b5-1 arrangement, often precede positive developments or indicate a belief that the stock is undervalued. This action suggests a favorable outlook from someone with deep knowledge of the company, making it a compelling 'buy' signal for seasoned investors.

Keywords

ALUMIS INC., ALMS, James B. Tananbaum, Insider Buying, Form 4, Beneficial Ownership, Director, 10% Owner, Stock Acquisition, Foresite Capital