XFOR · X4 Pharmaceuticals, Inc

The shares subject to the option shall vest in full on the one-year anniversary of the grant date, subject to the Reporting Person continuing to provide services through such date.

Sale of shares to cover personal income tax obligation upon settlement of restricted stock unit award.

The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions ranging from $4.21 to $4.31, inclusive. The Reporting Person undertakes to provide the Issuer, any security holder of the Issuer, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the range set forth in this footnote.

Of the shares of common stock reported, 96,627 shares represent restricted stock units.

Sale of shares to cover personal income tax obligation upon settlement of restricted stock unit award.

The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions ranging from $4.20 to $4.45, inclusive. The Reporting Person undertakes to provide the Issuer, any security holder of the Issuer, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the range set forth in this footnote.

Of the shares of common stock reported, 128,836 shares represent restricted stock units.

The shares subject to the option shall vest in full upon stockholder approval of an increase in the share reserve under the Companys Amended and Restated 2017 Equity Incentive Plan at the Companys 2026 annual meeting of stockholders, subject to the Reporting Person continuing to provide services through such date.

The shares subject to the option shall vest in full upon stockholder approval of an increase in the share reserve under the Companys Amended and Restated 2017 Equity Incentive Plan at the Companys 2026 annual meeting of stockholders, subject to the Reporting Person continuing to provide services through such date.

The shares subject to the option shall vest in full upon stockholder approval of an increase in the share reserve under the Companys Amended and Restated 2017 Equity Incentive Plan at the Companys 2026 annual meeting of stockholders, subject to the Reporting Person continuing to provide services through such date.

The shares subject to the option shall vest in full upon stockholder approval of an increase in the share reserve under the Companys Amended and Restated 2017 Equity Incentive Plan at the Companys 2026 annual meeting of stockholders, subject to the Reporting Person continuing to provide services through such date.

Represents stock options granted to the Reporting Person on August 12, 2025, which were subject to a performance-based vesting condition that was satisfied on October 29, 2025. One third of the shares subject to the option shall vest on August 12, 2026, with the remainder vesting in equal installments each successive month thereafter for a period of 24 months, subject to the Reporting Person continuing to provide services through each such date.

Represents stock options granted to the Reporting Person on August 12, 2025, which were subject to a performance-based vesting condition that was satisfied on October 29, 2025. One third of the shares subject to the option shall vest on August 12, 2026, with the remainder vesting in equal installments each successive month thereafter for a period of 24 months, subject to the Reporting Person continuing to provide services through each such date.

Represents stock options granted to the Reporting Person on August 12, 2025, which were subject to a performance-based vesting condition that was satisfied on October 29, 2025. One third of the shares subject to the option shall vest on August 12, 2026, with the remainder vesting in equal installments each successive month thereafter for a period of 24 months, subject to the Reporting Person continuing to provide services through each such date.

Consists of shares of the Issuer's common stock purchased in connection with the Issuer's public offering.

One half of the shares subject to the option shall vest on February 12, 2026, with the remainder vesting in equal installments in each successive month thereafter for a period of 12 months, subject to the Reporting Person continuing to provide services through each such date; provided that one half of the shares subject to the option shall vest immediately upon achievement of certain performance-based milestones prior to February 12, 2026.

One third of the shares subject to the option shall vest on August 12, 2026, with the remainder vesting in equal installments each successive month thereafter for a period of 24 months, subject to the Reporting Person continuing to provide services through each such date.

Represents restricted stock units (RSUs) granted to the Reporting Person. One third of the RSUs shall vest on February 12, 2026, with the remainder vesting in equal installments in each successive quarter thereafter for a period of 12 months, subject to the Reporting Person continuing to provide services through each such date and contingent upon approval of the grant at the Issuer's 2026 Annual Meeting of Stockholders.

One third of the shares subject to the option shall vest on August 12, 2026, with the remainder vesting in equal installments each successive month thereafter for a period of 24 months, subject to the Reporting Person continuing to provide services through each such date.

Represents restricted stock units (RSUs) granted to the Reporting Person. One third of the RSUs shall vest on each of August 12, 2026, August 12, 2027 and August 12, 2028, subject to the Reporting Person continuing to provide services through each such date and contingent upon approval of the grant at the Issuer's 2026 Annual Meeting of Stockholders.

Represents restricted stock units (RSUs) granted to the Reporting Person. One third of the RSUs shall vest on each of August 12, 2026, August 12, 2027 and August 12, 2028, subject to the Reporting Person continuing to provide services through each such date and contingent upon approval of the grant at the Issuer's 2026 Annual Meeting of Stockholders.

One half of the shares subject to the option shall vest on February 12, 2026, with the remainder vesting in equal installments in each successive month thereafter for a period of 12 months, subject to the Reporting Person continuing to provide services through each such date; provided that one half of the shares subject to the option shall vest immediately upon achievement of certain performance-based milestones prior to February 12, 2026.

One third of the shares subject to the option shall vest on August 12, 2026, with the remainder vesting in equal installments each successive month thereafter for a period of 24 months, subject to the Reporting Person continuing to provide services through each such date.

One third of the shares subject to the option shall vest on August 12, 2026, with the remainder vesting in equal installments each successive month thereafter for a period of 24 months, subject to the Reporting Person continuing to provide services through each such date.

Represents restricted stock units (RSUs) granted to the Reporting Person as an annual award for service on the Board of Directors. The RSUs will vest in full on the earlier of (i) the one-year anniversary of the grant date or (ii) the Issuer's next annual meeting of stockholders, subject to continued board service through the applicable vesting date. The RSUs will vest in full upon the occurrence of a change in control of the Issuer.

Represents restricted stock units (RSUs) granted to the Reporting Person as an annual award for service on the Board of Directors. The RSUs will vest in full on the earlier of (i) the one-year anniversary of the grant date or (ii) the Issuer's next annual meeting of stockholders, subject to continued board service through the applicable vesting date. The RSUs will vest in full upon the occurrence of a change in control of the Issuer.

Represents restricted stock units (RSUs) granted to the Reporting Person as an annual award for service on the Board of Directors. The RSUs will vest in full on the earlier of (i) the one-year anniversary of the grant date or (ii) the Issuer's next annual meeting of stockholders, subject to continued board service through the applicable vesting date. The RSUs will vest in full upon the occurrence of a change in control of the Issuer.

Represents restricted stock units (RSUs) granted to the Reporting Person as an annual award for service on the Board of Directors. The RSUs will vest in full on the earlier of (i) the one-year anniversary of the grant date or (ii) the Issuer's next annual meeting of stockholders, subject to continued board service through the applicable vesting date. The RSUs will vest in full upon the occurrence of a change in control of the Issuer.

Represents restricted stock units (RSUs) granted to the Reporting Person as an annual award for service on the Board of Directors. The RSUs will vest in full on the earlier of (i) the one-year anniversary of the grant date or (ii) the Issuer's next annual meeting of stockholders, subject to continued board service through the applicable vesting date. The RSUs will vest in full upon the occurrence of a change in control of the Issuer.

Represents restricted stock units (RSUs) granted to the Reporting Person as an annual award for service on the Board of Directors. The RSUs will vest in full on the earlier of (i) the one-year anniversary of the grant date or (ii) the Issuer's next annual meeting of stockholders, subject to continued board service through the applicable vesting date. The RSUs will vest in full upon the occurrence of a change in control of the Issuer.

Grant of restricted stock units to the Reporting Person under the Issuer's Amended and Restated 2017 Equity Incentive Plan with each restricted stock unit representing the right to receive one share of common stock on the applicable vesting date. No amount was paid upon the grant of the restricted stock units. The restricted stock units vest in three equal annual installments on May 10, 2026, May 10, 2027 and May 10, 2028, subject to the Reporting Person continuing to provide service as an employee of the Issuer through such date.

The reported amount has been adjusted to reflect a correction to the number of shares beneficially owned by the Reporting Person, which was inadvertently overstated by 855 shares on the Form 3 filed on June 3, 2025.

On May 16, 2025, the Reporting Person purchased shares of common stock through the Issuer's Amended and Restated 2017 Employee Stock Purchase Plan at a price of $2.482 per share. Such transaction was exempt under both Rule 16b-3(d) and Rule 16b-3(c) of the Securities Exchange Act of 1934, as amended.

Grant of restricted stock units to the Reporting Person under the Issuer's Amended and Restated 2017 Equity Incentive Plan with each restricted stock unit representing the right to receive one share of common stock on the applicable vesting date. No amount was paid upon the grant of the restricted stock units. The restricted stock units vest in three equal annual installments on February 12, 2026, February 12, 2027 and February 12, 2028, subject to the Reporting Person continuing to provide service as an employee of the Issuer through such date.

Grant of restricted stock units to the Reporting Person under the Issuer's Amended and Restated 2017 Equity Incentive Plan with each restricted stock unit representing the right to receive one share of common stock on the applicable vesting date. No amount was paid upon the grant of the restricted stock units. The restricted stock units vest in three equal annual installments on February 12, 2026, February 12, 2027 and February 12, 2028, subject to the Reporting Person continuing to provide service as an employee of the Issuer through such date.

Grant of restricted stock units to the Reporting Person under the Issuer's Amended and Restated 2017 Equity Incentive Plan with each restricted stock unit representing the right to receive one share of common stock on the applicable vesting date. No amount was paid upon the grant of the restricted stock units. The restricted stock units vest in three equal annual installments on February 12, 2026, February 12, 2027 and February 12, 2028, subject to the Reporting Person continuing to provide service as an employee of the Issuer through such date.

Grant of restricted stock units to the Reporting Person under the Issuer's Amended and Restated 2017 Equity Incentive Plan with each restricted stock unit representing the right to receive one share of common stock on the applicable vesting date. No amount was paid upon the grant of the restricted stock units. The restricted stock units vest in three equal annual installments on February 12, 2026, February 12, 2027 and February 12, 2028, subject to the Reporting Person continuing to provide service as an employee of the Issuer through such date.

Grant of restricted stock units to the Reporting Person under the Issuer's Amended and Restated 2017 Equity Incentive Plan with each restricted stock unit representing the right to receive one share of common stock on the applicable vesting date. No amount was paid upon the grant of the restricted stock units. The restricted stock units vest in three equal annual installments on February 12, 2026, February 12, 2027 and February 12, 2028, subject to the Reporting Person continuing to provide service as an employee of the Issuer through such date.

These transactions were made pursuant to a Rule 10b5-1 trading plan adopted by the Reporting Person on June 28, 2024.

The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions ranging from $0.447 to $0.47, inclusive. The Reporting Person undertakes to provide the Issuer, any security holder of the Issuer, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the range set forth in this footnote.

These transactions were made pursuant to a Rule 10b5-1 trading plan adopted by the Reporting Person on June 28, 2024.

The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions ranging from $0.4468 to $0.47, inclusive. The Reporting Person undertakes to provide the Issuer, any security holder of the Issuer, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the range set forth in this footnote.

These transactions were made pursuant to a Rule 10b5-1 trading plan adopted by the Reporting Person on June 28, 2024.

The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions ranging from $0.4472 to $0.47, inclusive. The Reporting Person undertakes to provide the Issuer, any security holder of the Issuer, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the range set forth in this footnote.

These transactions were made pursuant to a Rule 10b5-1 trading plan adopted by the Reporting Person on June 28, 2024.

The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions ranging from $0.4478 to $0.47, inclusive. The Reporting Person undertakes to provide the Issuer, any security holder of the Issuer, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the range set forth in this footnote.

These transactions were made pursuant to a Rule 10b5-1 trading plan adopted by the Reporting Person on June 28, 2024.

The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions ranging from $0.4475 to $0.47, inclusive. The Reporting Person undertakes to provide the Issuer, any security holder of the Issuer, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the range set forth in this footnote.

Represents shares earned upon the vesting of performance-based restricted stock units. The Compensation Committee of the Board of Directors of the Issuer certified the achievement of a performance condition, which occurred upon the acceptance by the European Medicines Agency of the Issuer's Marketing Authorization Application for mavorixafor for the treatment of WHIM syndrome.

Represents shares earned upon the vesting of performance-based restricted stock units. The Compensation Committee of the Board of Directors of the Issuer certified the achievement of a performance condition, which occurred upon the acceptance by the European Medicines Agency of the Issuer's Marketing Authorization Application for mavorixafor for the treatment of WHIM syndrome.

Represents shares earned upon the vesting of performance-based restricted stock units. The Compensation Committee of the Board of Directors of the Issuer certified the achievement of a performance condition, which occurred upon the acceptance by the European Medicines Agency of the Issuer's Marketing Authorization Application for mavorixafor for the treatment of WHIM syndrome.

Represents shares earned upon the vesting of performance-based restricted stock units. The Compensation Committee of the Board of Directors of the Issuer certified the achievement of a performance condition, which occurred upon the acceptance by the European Medicines Agency of the Issuer's Marketing Authorization Application for mavorixafor for the treatment of WHIM syndrome.

Represents shares earned upon the vesting of performance-based restricted stock units. The Compensation Committee of the Board of Directors of the Issuer certified the achievement of a performance condition, which occurred upon the acceptance by the European Medicines Agency of the Issuer's Marketing Authorization Application for mavorixafor for the treatment of WHIM syndrome.

The Reporting Person purchased shares of common stock through the Issuer's Amended and Restated 2017 Employee Stock Purchase Plan. Such purchases were inadvertently omitted from previous Form 4 filings and are now being reported.

These transactions were made pursuant to a Rule 10b5-1 trading plan adopted by the Reporting Person on June 28, 2024.

The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions ranging from $0.364 to $0.41, inclusive. The Reporting Person undertakes to provide the Issuer, any security holder of the Issuer, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the range set forth in this footnote.

These transactions were made pursuant to a Rule 10b5-1 trading plan adopted by the Reporting Person on June 28, 2024.

The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions ranging from $0.5424 to $0.5806, inclusive. The Reporting Person undertakes to provide the Issuer, any security holder of the Issuer, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the range set forth in this footnote.