SCHEDULE 13G

X4 Pharmaceuticals Inc

Common Stock, par value $0.001 per share · CUSIP: 98420X202

Event date: 2025-08-13

Reporting persons may disclose overlapping interests. Their amounts are shown individually and are not added into a filing total.

Filing-level shares

Unavailable

Percent of class

Unavailable

• BIOTECHNOLOGY VALUE FUND L P

  Shares: 1,168,649.00 · Class: 5.2%

• BVF I GP LLC

  Shares: 1,168,649.00 · Class: 5.2%

• BIOTECHNOLOGY VALUE FUND II LP

  Shares: 906,855.00 · Class: 4.0%

• BVF II GP LLC

  Shares: 906,855.00 · Class: 4.0%

• Biotechnology Value Trading Fund OS LP

  Shares: 123,369.00 · Class: 0.6%

• BVF Partners OS Ltd.

  Shares: 123,369.00 · Class: 0.6%

• BVF GP HOLDINGS LLC

  Shares: 2,075,504.00 · Class: 9.2%

• BVF PARTNERS L P/IL

  Shares: 2,243,659.00 · Class: 9.9%

• BVF INC/IL

  Shares: 2,243,659.00 · Class: 9.9%

• LAMPERT MARK N

  Shares: 2,243,659.00 · Class: 9.9%

Amounts are as disclosed in this filing. Schedule type alone does not establish investment intent.