BL · Blackline, Inc.

The transaction reported on this Form 4 was effectuated pursuant to a Rule 10b5-1 trading plan adopted by the reporting person on February 19, 2026.

The reported shares were withheld to cover the Reporting Person's tax liability in connection with the vesting of restricted stock units.

Includes 459 shares acquired on May 8, 2026, through the Issuer's Employee Stock Purchase Plan in a transaction that was exempt under both Rule 16b-3(d) and Rule 16b-3(c).

The reported shares were withheld to cover the Reporting Person's tax liability in connection with the vesting of restricted stock units.

Includes 459 shares acquired on May 8, 2026, through the Issuer's Employee Stock Purchase Plan in a transaction that was exempt under both Rule 16b-3(d) and Rule 16b-3(c).

The reported shares were withheld to cover the Reporting Person's tax liability in connection with the vesting of restricted stock units.

The reported shares were withheld to cover the Reporting Person's tax liability in connection with the vesting of restricted stock units.

Includes 459 shares acquired on May 8, 2026, through the Issuer's Employee Stock Purchase Plan in a transaction that was exempt under both Rule 16b-3(d) and Rule 16b-3(c).

The reported shares were withheld to cover the Reporting Person's tax liability in connection with the vesting of restricted stock units.

Includes 459 shares acquired on May 8, 2026, through the Issuer's Employee Stock Purchase Plan in a transaction that was exempt under both Rule 16b-3(d) and Rule 16b-3(c).

The reported shares were withheld to cover the Reporting Person's tax liability in connection with the vesting of restricted stock units.

The reported shares were withheld to cover the Reporting Person's tax liability in connection with the vesting of restricted stock units.

The reported shares were withheld to cover the Reporting Person's tax liability in connection with the vesting of restricted stock units.

The reported shares were withheld to cover the Reporting Person's tax liability in connection with the vesting of restricted stock units.

The reported shares were withheld to cover the Reporting Person's tax liability in connection with the vesting of restricted stock units.

The reported shares were withheld to cover the Reporting Person's tax liability in connection with the vesting of restricted stock units.

The reported shares were withheld to cover the Reporting Person's tax liability in connection with the vesting of restricted stock units.

The reported shares were withheld to cover the Reporting Person's tax liability in connection with the vesting of restricted stock units.

The reported shares were withheld to cover the Reporting Person's tax liability in connection with the vesting of restricted stock units.

The reported shares were withheld to cover the Reporting Person's tax liability in connection with the vesting of restricted stock units.

The reported shares were withheld to cover the Reporting Person's tax liability in connection with the vesting of restricted stock units.

The reported shares were withheld to cover the Reporting Person's tax liability in connection with the vesting of restricted stock units.

The reported shares were withheld to cover the Reporting Person's tax liability in connection with the vesting of restricted stock units.

The reported shares were withheld to cover the Reporting Person's tax liability in connection with the vesting of restricted stock units.

The reported shares were withheld to cover the Reporting Person's tax liability in connection with the vesting of restricted stock units.

The reported shares were withheld to cover the Reporting Person's tax liability in connection with the vesting of restricted stock units.

The reported transaction represents a bona fide gift made by the reporting person.

Reflects an automatic annual restricted stock unit ("RSU") award pursuant to the Issuer's Outside Director Compensation Policy.

The reported securities awarded on May 7, 2026 (the "Award Date") represent RSUs which vest in full upon the earlier of the one (1) year anniversary of the Award Date or the day prior to the Issuer's next annual meeting of the stockholders and in each case subject to the Reporting Person's continued service on the Issuer's board of directors through each vesting date.

Reflects an automatic annual restricted stock unit ("RSU") award pursuant to the Issuer's Outside Director Compensation Policy.

The reported securities awarded on May 7, 2026 (the "Award Date") represent RSUs which vest in full upon the earlier of the one (1) year anniversary of the Award Date or the day prior to the Issuer's next annual meeting of the stockholders and in each case subject to the Reporting Person's continued service on the Issuer's board of directors through each vesting date.

Reflects an automatic annual restricted stock unit ("RSU") award pursuant to the Issuer's Outside Director Compensation Policy.

The reported securities awarded on May 7, 2026 (the "Award Date") represent RSUs which vest in full upon the earlier of the one (1) year anniversary of the Award Date or the day prior to the Issuer's next annual meeting of the stockholders and in each case subject to the Reporting Person's continued service on the Issuer's board of directors through each vesting date.

Reflects an automatic annual restricted stock unit ("RSU") award pursuant to the Issuer's Outside Director Compensation Policy.

The reported securities awarded on May 7, 2026 (the "Award Date") represent RSUs which vest in full upon the earlier of the one (1) year anniversary of the Award Date or the day prior to the Issuer's next annual meeting of the stockholders and in each case subject to the Reporting Person's continued service on the Issuer's board of directors through each vesting date.

Reflects an automatic annual restricted stock unit ("RSU") award pursuant to the Issuer's Outside Director Compensation Policy.

The reported securities awarded on May 7, 2026 (the "Award Date") represent RSUs which vest in full upon the earlier of the one (1) year anniversary of the Award Date or the day prior to the Issuer's next annual meeting of the stockholders and in each case subject to the Reporting Person's continued service on the Issuer's board of directors through each vesting date.

Reflects an automatic annual restricted stock unit ("RSU") award pursuant to the Issuer's Outside Director Compensation Policy.

The reported securities awarded on May 7, 2026 (the "Award Date") represent RSUs which vest in full upon the earlier of the one (1) year anniversary of the Award Date or the day prior to the Issuer's next annual meeting of the stockholders and in each case subject to the Reporting Person's continued service on the Issuer's board of directors through each vesting date.

Reflects an automatic annual restricted stock unit ("RSU") award pursuant to the Issuer's Outside Director Compensation Policy.

The reported securities awarded on May 7, 2026 (the "Award Date") represent RSUs which vest in full upon the earlier of the one (1) year anniversary of the Award Date or the day prior to the Issuer's next annual meeting of the stockholders and in each case subject to the Reporting Person's continued service on the Issuer's board of directors through each vesting date.

Reflects an automatic annual restricted stock unit ("RSU") award pursuant to the Issuer's Outside Director Compensation Policy.

The reported securities awarded on May 7, 2026 (the "Award Date") represent RSUs which vest in full upon the earlier of the one (1) year anniversary of the Award Date or the day prior to the Issuer's next annual meeting of the stockholders and in each case subject to the Reporting Person's continued service on the Issuer's board of directors through each vesting date.

Reflects an automatic annual restricted stock unit ("RSU") award pursuant to the Issuer's Outside Director Compensation Policy.

The reported securities awarded on May 7, 2026 (the "Award Date") represent RSUs which vest in full upon the earlier of the one (1) year anniversary of the Award Date or the day prior to the Issuer's next annual meeting of the stockholders and in each case subject to the Reporting Person's continued service on the Issuer's board of directors through each vesting date.

Reflects an automatic annual restricted stock unit ("RSU") award pursuant to the Issuer's Outside Director Compensation Policy.

The reported securities awarded on May 7, 2026 (the "Award Date") represent RSUs which vest in full upon the earlier of the one (1) year anniversary of the Award Date or the day prior to the Issuer's next annual meeting of the stockholders and in each case subject to the Reporting Person's continued service on the Issuer's board of directors through each vesting date.

Reflects an automatic annual restricted stock unit ("RSU") award pursuant to the Issuer's Outside Director Compensation Policy.

The reported securities awarded on May 7, 2026 (the "Award Date") represent RSUs which vest in full upon the earlier of the one (1) year anniversary of the Award Date or the day prior to the Issuer's next annual meeting of the stockholders and in each case subject to the Reporting Person's continued service on the Issuer's board of directors through each vesting date.

Each share is represented by a Restricted Stock Unit ("RSU"). 25% of the RSUs will vest on the one (1) year anniversary of February 20, 2026 (the "RSU Vesting Commencement Date"), and 1/16th of the RSUs will vest every three months thereafter on the same day of the month as the RSU Vesting Commencement Date, subject to the reporting person's continued service through each applicable vesting date.

Each share is represented by a Restricted Stock Unit ("RSU"). 25% of the RSUs will vest on the one (1) year anniversary of February 20, 2026 (the "RSU Vesting Commencement Date"), and 1/16th of the RSUs will vest every three months thereafter on the same day of the month as the RSU Vesting Commencement Date, subject to the reporting person's continued service through each applicable vesting date.

Each share is represented by a Restricted Stock Unit ("RSU"). 25% of the RSUs will vest on the one (1) year anniversary of February 20, 2026 (the "RSU Vesting Commencement Date"), and 1/16th of the RSUs will vest every three months thereafter on the same day of the month as the RSU Vesting Commencement Date, subject to the reporting person's continued service through each applicable vesting date.

Each share is represented by a Restricted Stock Unit ("RSU"). 25% of the RSUs will vest on the one (1) year anniversary of February 20, 2026 (the "RSU Vesting Commencement Date"), and 1/16th of the RSUs will vest every three months thereafter on the same day of the month as the RSU Vesting Commencement Date, subject to the reporting person's continued service through each applicable vesting date.

Each share is represented by a Restricted Stock Unit ("RSU"). 25% of the RSUs will vest on the one (1) year anniversary of February 20, 2026 (the "RSU Vesting Commencement Date"), and 1/16th of the RSUs will vest every three months thereafter on the same day of the month as the RSU Vesting Commencement Date, subject to the reporting person's continued service through each applicable vesting date.

Each share is represented by a Restricted Stock Unit ("RSU"). 25% of the RSUs will vest on the one (1) year anniversary of February 20, 2026 (the "RSU Vesting Commencement Date"), and 1/16th of the RSUs will vest every three months thereafter on the same day of the month as the RSU Vesting Commencement Date, subject to the reporting person's continued service through each applicable vesting date.

Each share is represented by a Restricted Stock Unit ("RSU"). 25% of the RSUs will vest on the one (1) year anniversary of February 20, 2026 (the "RSU Vesting Commencement Date"), and 1/16th of the RSUs will vest every three months thereafter on the same day of the month as the RSU Vesting Commencement Date, subject to the reporting person's continued service through each applicable vesting date.

This Form 4 reports an initial grant of restricted stock units to Ms. Prichard following her appointment to the Issuer's board of directors on March 11, 2026. The filing was delayed due to a procedural delay in Ms. Prichard receiving the requisite EDGAR access codes from the SEC. This Form 4 was filed promptly upon receipt of the codes.

Represents an initial restricted stock unit ("RSU") award issued pursuant to the Issuer's Outside Director Compensation Policy.

Each RSU represents a contingent right to receive one share of the Issuer's common stock upon settlement. 100% of the RSUs will vest the day prior to the Issuer's next annual stockholder meeting, subject to the reporting person's continued service through the applicable vesting date.

This Form 4 reports an initial grant of restricted stock units to Mr. Duncan following his appointment to the Issuer's board of directors on March 11, 2026. The filing was delayed due to a procedural delay in Mr. Duncan receiving the requisite EDGAR access codes from the SEC. This Form 4 was filed promptly upon receipt of the codes.

Represents an initial stock unit ("RSU") award issued pursuant to the Issuer's Outside Director Compensation Policy.

Each RSU represents a contingent right to receive one share of the Issuer's common stock upon settlement. 100% of the RSUs will vest the day prior to the Issuer's next annual stockholder meeting, subject to the reporting person's continued service through the applicable vesting date.

The reported shares relate to the portion of a Performance Based Restricted Stock Unit ("PRSU") granted on March 7, 2023 that has vested based on the Issuer's achievement of certain fiscal 2023 performance targets that were set by the Compensation Committee at the time of grant.