Former Officer Sara Bonstein Files Form 144 to Sell $1.12M in Insmed Inc (INSM) for Tax Withholding

Executive Summary

On November 3, 2026, Sara Bonstein, a former officer of INSMED Inc ($INSM), filed a Form 144 notice of proposed sale covering 10,261 shares of common stock through Merrill Lynch. The aggregate market value of the proposed transaction is $1,121,629, implying an estimated price per share of approximately $109.31.

Transaction Details

• Security: Common Stock
• Shares Proposed for Sale: 10,261
• Aggregate Market Value: $1,121,629
• Approximate Sale Date: November 3, 2026
• Acquisition Origin: Acquired on October 30, 2026, via Stock Plan Activity (Restricted Stock Unit vesting) from the issuer.
• Remarks: The filing notes that the shares are being sold specifically to satisfy tax withholding obligations triggered by RSU vesting and to cover related broker fees.

Market and Trading Impact

• Significance Level: Low
• Context: The sale represents approximately 0.005% of the 219,380,309 shares outstanding, presenting minimal dilution or float absorption impact.
• Intent: Because this is an automated or routine sell-to-cover transaction for tax withholding by a former officer, it does not represent discretionary insider sentiment regarding the company's valuation or prospects.