Luo Mary Z. 4

What Happened
Jack Y. Zhang, a reported 10% owner of Amphastar Pharmaceuticals (AMPH), had 12,692 shares withheld to satisfy tax liabilities related to the vesting of restricted stock units (RSUs). The withholding occurred on March 15, 2026, at a per-share value of $18.18 — 9,784 shares ($177,873) and 2,908 shares ($52,867), for a combined value of $230,740. This was a tax-withholding disposition (code F), not an open-market sale.

Key Details

• Transaction date: 2026-03-15; Form 4 filed: 2026-03-17 (timely filing).
• Withheld shares: 9,784 @ $18.18 ($177,873) and 2,908 @ $18.18 ($52,867); total 12,692 shares worth $230,740.
• Transaction code: F (shares withheld to satisfy tax liability on RSU vesting; sometimes called net settlement).
• Shares owned after the transaction: not provided in the information supplied.
• Footnotes: F1 confirms shares were withheld to satisfy tax liability on RSU vesting; F2 notes securities are held of record by Mary Z. Luo (reporting persons are husband and wife); F3 notes some shares are held of record by Applied Physics and Chemistry Laboratories, Inc., owned by the reporting persons and a related trust.

Context
Withholding shares to cover taxes is a common administrative step when RSUs vest and does not represent an open-market sale or a directional bet on the stock. As a 10% owner, Zhang's holdings reflect substantial, long-term ownership structures (including spouse and entity-held shares), so these withholding transactions are procedural rather than indicative of a change in investment view.