SCHEDULE: Alector Insider Arnon Rosenthal Boosts Stake to 7.4%

Arnon Rosenthal, a key insider at Alector, Inc., reported beneficial ownership of 7.4% of the company's common stock as of December 31, 2025.

Summary

• Arnon Rosenthal beneficially owns 8,213,925 shares of Alector, Inc. common stock.
• This ownership represents 7.4% of the company's outstanding common stock, based on 109,151,472 shares outstanding as of October 31, 2025.
• Sole voting and dispositive power is held over 4,283,550 shares, which includes 1,736,295 shares held directly, 132,804 shares from restricted stock units vesting within 60 days, and 2,414,451 shares from options exercisable within 60 days.
• Shared voting and dispositive power is held over 3,930,375 shares, which are held by various family trusts for which Arnon Rosenthal serves as trustee: The Rosenthal Family Revocable Trust (1,972,875 shares), The Adi Rosenthal 2007 Trust (652,500 shares), The Noam Rosenthal 2007 Trust (652,500 shares), and The Shani Rosenthal 2007 Trust (652,500 shares).

Sentiment

Score: 7

Explanation: StockSavvy.ai views this filing positively as it indicates a significant and sustained insider stake by Arnon Rosenthal, suggesting continued confidence in Alector, Inc.'s future.

Positives

• Increased insider ownership, particularly from a key individual like Arnon Rosenthal, can signal confidence in the company's future prospects.

Future Outlook

This filing does not contain forward-looking statements or guidance regarding the company's operational or financial performance.

Industry Context

StockSavvy.ai notes that insider ownership filings like this Schedule 13G are routine disclosures required when an individual's beneficial ownership crosses certain thresholds. While not directly indicative of broader industry trends, significant insider stakes can sometimes be interpreted by the market as a sign of management's conviction in the company's long-term value, especially in the biotechnology sector where R&D timelines are extensive.

Related Party Transactions

• Arnon Rosenthal holds shared voting and dispositive power over 3,930,375 shares held by The Rosenthal Family Revocable Trust, The Adi Rosenthal 2007 Trust, The Noam Rosenthal 2007 Trust, and The Shani Rosenthal 2007 Trust, for which he serves as trustee.

Stakeholder Impact

• Shareholders may view the significant insider ownership by Arnon Rosenthal as a positive signal, indicating alignment of interests between management and investors.

Key Dates

Recommendation

The filing indicates a significant and stable insider ownership position by Arnon Rosenthal, which can be a positive signal of confidence. However, a Schedule 13G filing primarily reports ownership and does not provide new operational or financial data to warrant a 'buy' or 'sell' recommendation. Investors should 'hold' and consider this information in conjunction with the company's financial performance, strategic developments, and broader market conditions.

Keywords

Alector Inc., Arnon Rosenthal, Beneficial Ownership, Schedule 13G, Common Stock, Insider Ownership, Equity Stake