X0306 4 2019-06-17 0 0001501697 X4 Pharmaceuticals, Inc XFOR 0001738081 Mostafa Adam S. C/O X4 PHARMACEUTICALS, INC. 955 MASSACHUSETTS AVENUE, 4TH FLOOR CAMBRIDGE MA 02139 0 1 0 0 CFO and Treasurer Common Stock 2019-06-17 4 A 0 10564 0.00 A 10564 D Stock Option (right to buy) 14.75 2019-06-17 4 A 0 15847 0.00 A 2029-06-17 Common Stock 15847 15847 D Grant of restricted stock units to the Reporting Person under the Issuer's 2017 Equity Incentive Plan, with each restricted stock unit representing the contingent right to receive one share of common stock on the applicable vesting date. No amount was paid upon grant of the units. The restricted stock units vest in four equal annual installments on June 30, 2020, June 30, 2021, June 30, 2022 and June 30, 2023, subject to the Reporting Person continuing to provide services through each such date. Represents unvested restricted stock units. 25% of the shares subject to the option shall vest on June 17, 2020, with the remainder vesting in equal installments of 2.0833% of the shares subject to the option on the last day of each successive month thereafter for a period of 36 months, subject to the Reporting Person continuing to provide services through each such date. /s/ Adam S. Mostafa 2019-06-19