ATEN · A10 Networks, Inc.

Shares withheld, on a non-discretionary basis, for tax purposes related to a July 1, 2022 restricted stock unit grant that vested on July 5, 2026.

Includes 1,042 shares acquired by the Reporting Person on May 31, 2026 pursuant to the Issuer's Employee Stock Purchase Plan.

This amendment to the original Form 4 filed on May 15, 2026 is being filed to correct the price reported in Column 4 of Table I in connection with the shares withheld, on a non-discretionaly basis, for tax purposes related to a February 6, 2025 performance-based restricted stock unit grant and a February 12, 2026 performance-based restricted stock unti grant, each that vested on May 14, 2026.

This amendment to the original Form 4 filed on May 15, 2026 is being filed to correct the price reported in Column 4 of Table I in connection with the shares withheld, on a non-discretionary basis, for tax purposes related to a February 6, 2025 performance-based restricted stock unit grant and a February 12, 2026 performance-based restricted stock unti grant, each that vested on May 14, 2026.

This amendment to the original Form 4 filed on May 15, 2026 is being filed to correct the number of shares withheld, on a non-discretionary basis, for tax purposes related to a February 12, 2026 perfomance-based restricted stock unit grant that vested on May 14, 2026.

This amendment to the original Form 4 filed on May 15, 2026 is also being filed to correc the price reported on Column 4 of Table I in connection with the shares withheld, on a non-discretionary basis, for tax purposes related to a February 12, 2026 performance-based restricted stock unit grant that vested on May 14, 2026.

The total number of shares reported on Column 5 of Table I of this amendment is the total owned by the reporting person as of May 15, 20206, which reflects the corrected number of shares withheld.

Includes 987 shares and 943 shares automatically withheld, on a non-discretionary basis, for tax purposes related to a February 6, 2025 performance-based restricted stock unit grant and a February 12, 2026 performance-based restricted stock unit grant, respectively, each that vested on May 5, 2026.

Includes 2,458 shares and 536 shares automatically withheld, on a non-discretionary basis, for tax purposes related to a September 30, 2025 performance-based restricted stock unit grant and a February 12, 2026 performance-based restricted stock unit grant, respectively, each that vested on May 5, 2026.

Includes 16,130 shares and 16,728 shares automatically withheld, on a non-discretionary basis, for tax purposes related to a February 6, 2025 performance-based restricted stock unit grant and a February 12, 2026 performance-based restricted stock unit grant, respectively, each that vested on May 5, 2026.

Performance-Based Restricted Stock Units were previously reported on February 10, 2025, each of which represents a contingent right to receive one share of common stock of ATEN, with vesting subject to the achievement of specified levels of the volume weighted average closing prices of a share of ATEN common stock during any one hundred (100) day trading period between February 6, 2025 and February 6, 2029. The first achievement date occurred on April 16, 2026, as certified by the compensation committee of ATEN, resulting in 3,882 units meeting the appropriate performance-based conditions. However, these shares remain subject to time-based vesting conditions and will therefore vest as to one-half (1/2) on May 5, 2026 and an additional one-fourth (1/4) on each of the first and second anniversaries of April 16, 2026, subject to continued employment. These shares are reflected on Table I.

Performance-Based Restricted Stock Units that were previously reported on February 13, 2026, each of which represents a contingent right to receive one share of common stock of ATEN, with vesting subject to the achievement of specified levels of the volume weighted average closing prices of a share of ATEN common stock during any one hundred (100) day trading period between February 12, 2026 and February 12, 2030. The first achievement date occurred on April 22, 2026, as certified by the compensation committee of ATEN, resulting in 65,753 units meeting the appropriate performance-based conditions. However, these shares remain subject to time-based vesting conditions and will therefore vest as to one-half (1/2) on May 5, 2026 and an additional one-fourth (1/4) on each of the first and second anniversaries of April 22, 2026, subject to continued employment. These shares are reflected on Table I.

Performance-Based Restricted Stock Units were previously reported on October 2, 2025, each of which represents a contingent right to receive one share of common stock of ATEN, with vesting subject to the achievement of a specified level of the volume weighted average closing price of a share of ATEN common stock during any one hundred (100) day trading period between September 30, 2025 and September 30, 2029. The achievement date occurred on April 16, 2026, as certified by the compensation committee of ATEN, resulting in 13,706 units meeting the appropriate performance-based conditions. However, these shares remain subject to time-based vesting conditions and will therefore vest as to one-half (1/2) on May 5, 2026 and an additional one-fourth (1/4) on each of the first and second anniversaries of April 16, 2026, subject to continued employment. These shares are reflected on Table I.

Performance-Based Restricted Stock Units were previously reported on February 10, 2025, each of which represents a contingent right to receive one share of common stock of ATEN, with vesting subject to the achievement of specified levels of the volume weighted average closing prices of a share of ATEN common stock during any one hundred (100) day trading period between February 6, 2025 and February 6, 2029. The first achievement date occurred on April 16, 2026, as certified by the compensation committee of ATEN, resulting in 3,882 units meeting the appropriate performance-based conditions. However, these shares remain subject to time-based vesting conditions and will therefore vest as to one-half (1/2) on May 5, 2026 and an additional one-fourth (1/4) on each of the first and second anniversaries of April 16, 2026, subject to continued employment. These shares are reflected on Table I.

Performance-Based Restricted Stock Units that were previously reported on February 13, 2026, each of which represents a contingent right to receive one share of common stock of ATEN, with vesting subject to the achievement of specified levels of the volume weighted average closing prices of a share of ATEN common stock during any one hundred (100) day trading period between February 12, 2026 and February 12, 2030. The first achievement date occurred on April 22, 2026, as certified by the compensation committee of ATEN, resulting in 3,707 units meeting the appropriate performance-based conditions. However, these shares remain subject to time-based vesting conditions and will therefore vest as to one-half (1/2) on May 5, 2026 and an additional one-fourth (1/4) on each of the first and second anniversaries of April 22, 2026, subject to continued employment. These shares are reflected on Table I.

Performance-Based Restricted Stock Units were previously reported on October 2, 2025, each of which represents a contingent right to receive one share of common stock of ATEN, with vesting subject to the achievement of a specified level of the volume weighted average closing price of a share of ATEN common stock during any one hundred (100) day trading period between September 30, 2025 and September 30, 2029. The achievement date occurred on April 16, 2026, as certified by the compensation committee of ATEN, resulting in 13,706 units meeting the appropriate performance-based conditions. However, these shares remain subject to time-based vesting conditions and will therefore vest as to one-half (1/2) on May 5, 2026 and an additional one-fourth (1/4) on each of the first and second anniversaries of April 16, 2026, subject to continued employment. These shares are reflected on Table I.

Performance-Based Restricted Stock Units were previously reported on February 10, 2025, each of which represents a contingent right to receive one share of common stock of ATEN, with vesting subject to the achievement of specified levels of the volume weighted average closing prices of a share of ATEN common stock during any one hundred (100) day trading period between February 6, 2025 and February 6, 2029. The first achievement date occurred on April 16, 2026, as certified by the compensation committee of ATEN, resulting in 63,406 units meeting the appropriate performance-based conditions. However, these shares remain subject to time-based vesting conditions and will therefore vest as to one-half (1/2) on May 5, 2026 and an additional one-fourth (1/4) on each of the first and second anniversaries of April 16, 2026, subject to continued employment. These shares are reflected on Table I.

This is the weighted average price of the shares sold, which ranged from $26.88 to $27.41 per share. Upon request by the Commission staff, the Issuer, or a security holder of the Issuer, the Reporting Person will provide full information regarding the number of shares sold at each separate price within the range set forth in this Form 4.

Performance-Based Restricted Stock Units that were previously reported on February 13, 2026, each of which represents a contingent right to receive one share of common stock of ATEN, with vesting subject to the achievement of specified levels of the volume weighted average closing prices of a share of ATEN common stock during any one hundred (100) day trading period between February 12, 2026 and February 12, 2030. The first achievement date occurred on April 22, 2026, as certified by the compensation committee of ATEN, resulting in 65,753 units meeting the appropriate performance-based conditions. However, these shares remain subject to time-based vesting conditions and will therefore vest as to one-half (1/2) on May 5, 2026 and an additional one-fourth (1/4) on each of the first and second anniversaries of April 22, 2026, subject to continued employment. These shares are reflected on Table I.

Performance-Based Restricted Stock Units that were previously reported on February 13, 2026, each of which represents a contingent right to receive one share of common stock of ATEN, with vesting subject to the achievement of specified levels of the volume weighted average closing prices of a share of ATEN common stock during any one hundred (100) day trading period between February 12, 2026 and February 12, 2030. The first achievement date occurred on April 22, 2026, as certified by the compensation committee of ATEN, resulting in 2,989 units meeting the appropriate performance-based conditions. However, these shares remain subject to time-based vesting conditions and will therefore vest as to one-half (1/2) on May 5, 2026 and an additional one-fourth (1/4) on each of the first and second anniversaries of April 22, 2026, subject to continued employment. These shares are reflected on Table I.

Performance-Based Restricted Stock Units were previously reported on February 10, 2025, each of which represents a contingent right to receive one share of common stock of ATEN, with vesting subject to the achievement of specified levels of the volume weighted average closing prices of a share of ATEN common stock during any one hundred (100) day trading period between February 6, 2025 and February 6, 2029. The first achievement date occurred on April 16, 2026, as certified by the compensation committee of ATEN, resulting in 63,406 units meeting the appropriate performance-based conditions. However, these shares remain subject to time-based vesting conditions and will therefore vest as to one-half (1/2) on May 5, 2026 and an additional one-fourth (1/4) on each of the first and second anniversaries of April 16, 2026, subject to continued employment. These shares are reflected on Table I.

Performance-Based Restricted Stock Units that were previously reported on February 13, 2026, each of which represents a contingent right to receive one share of common stock of ATEN, with vesting subject to the achievement of specified levels of the volume weighted average closing prices of a share of ATEN common stock during any one hundred (100) day trading period between February 12, 2026 and February 12, 2030. The first achievement date occurred on April 22, 2026, as certified by the compensation committee of ATEN, resulting in 2,989 units meeting the appropriate performance-based conditions. However, these shares remain subject to time-based vesting conditions and will therefore vest as to one-half (1/2) on May 5, 2026 and an additional one-fourth (1/4) on each of the first and second anniversaries of April 22, 2026, subject to continued employment. These shares are reflected on Table I.

Performance-Based Restricted Stock Units that were previously reported on February 13, 2026, each of which represents a contingent right to receive one share of common stock of ATEN, with vesting subject to the achievement of specified levels of the volume weighted average closing prices of a share of ATEN common stock during any one hundred (100) day trading period between February 12, 2026 and February 12, 2030. The first achievement date occurred on April 22, 2026, as certified by the compensation committee of ATEN, resulting in 3,707 units meeting the appropriate performance-based conditions. However, these shares remain subject to time-based vesting conditions and will therefore vest as to one-half (1/2) on May 5, 2026 and an additional one-fourth (1/4) on each of the first and second anniversaries of April 22, 2026, subject to continued employment. These shares are reflected on Table I.

Each share is represented by a Restricted Stock Unit ("RSU"). The RSUs will vest on the earlier of April 22, 2027 or the date of the Issuer's next Annual Meeting, provided that the Reporting Person continues to serve through each such vesting date.

Represents restricted stock units granted to Mr. Chung as part of the director compensation program. The restricted stock units will vest on the earlier of April 22, 2027, or the date of the Issuer's next Annual Meeting, and will settle solely by delivery of an equal number of shares of Common Stock provided that Mr. Chung remains in continuous service with the Issuer through the vesting date.

The 207,298 shares and restricted stock units are held in the name of Mr. Chung, which are held for the benefit of Summit Partners, L.P.

Mr. Chung holds any Common Stock and restricted stock units for the benefit of Summit Partners, L.P. and Mr. Chung disclaims beneficial ownership of the shares of common stock and the restricted stock units, except to the extent of their pecuniary interest therein.

Each share is represented by a Restricted Stock Unit ("RSU"). The RSUs will vest on the earlier of April 22, 2027 or the date of the Issuer's next Annual Meeting, provided that the Reporting Person continues to serve through each such vesting date.

Each share is represented by a Restricted Stock Unit ("RSU"). The RSUs will vest on the earlier of April 22, 2027 or the date of the Issuer's next Annual Meeting, provided that the Reporting Person continues to serve through each such vesting date.

Shares automatically withheld, on a non-discretionary basis, for tax purposes related to performance-based restricted stock units granted on February 21, 2023, which vested on February 28, 2026.

Shares automatically withheld, on a non-discretionary basis, for tax purposes related to performance-based restricted stock units granted on February 21, 2023, which vested on February 28, 2026.

Shares automatically withheld, on a non-discretionary basis, for tax purposes related to performance-based restricted stock units granted on January 25, 2022, which vested on February 24, 2026.

The sales reported on this Form 4 were effected pursuant to a Rule 10b5-1 trading plan adopted by the Reporting Person on September 12, 2025.

This is the weighted average price of the shares sold, which ranged from $20.23 to $20.72 per share. Upon request by the Commission staff, the Issuer, or a security holder of the Issuer, the Reporting Person will provide full information regarding the number of shares sold at each separate price within the range set forth in this Form 4.

Each share is represented by a Performance-based Restricted Stock Unit ("PSU").

Grant of 7,771 PSUs, each of which represents a contingent right to receive one share of common stock of ATEN, with vesting subject to the achievement of specified levels of the volume weighted average closing prices of a share of ATEN common stock during any one hundred (100) day trading period between February 12, 2026 and February 12, 2030 (each, a "Performance Milestone"). Upon achievement of a Performance Milestone, vesting is subject to continued employment with the Company through the applicable vesting date, the first fifty percent ( 50%) of which will occur within thirty (30) days of achievment of the applicable milestone and the balance to vest twenty-five percent (25%) on each of the first and second anniversaries of achievement of the corresponding Performance Milestone.

Each share is represented by a Performance-based Restricted Stock Unit ("PSU").

Grant of 5,978 PSUs, each of which represents a contingent right to receive one share of common stock of ATEN, with vesting subject to the achievement of specified levels of the volume weighted average closing prices of a share of ATEN common stock during any one hundred (100) day trading period between February 12, 2026 and February 12, 2030 (each, a "Performance Milestone"). Upon achievement of a Performance Milestone, vesting is subject to continued employment with the Company through the applicable vesting date, the first fifty percent ( 50%) of which will occur within thirty (30) days of achievment of the applicable milestone and the balance to vest twenty-five percent (25%) on each of the first and second anniversaries of achievement of the corresponding Performance Milestone.

Each share is represented by a Performance-based Restricted Stock Unit ("PSU").

Grant of 131,516 PSUs, each of which represents a contingent right to receive one share of common stock of ATEN, with vesting subject to the achievement of specified levels of the volume weighted average closing prices of a share of ATEN common stock during any one hundred (100) day trading period between February 12, 2026 and February 12, 2030 (each, a "Performance Milestone"). Upon achievement of a Performance Milestone, vesting is subject to continued employment with the Company through the applicable vesting date, the first fifty percent ( 50%) of which will occur within thirty (30) days of achievment of the applicable milestone and the balance to vest twenty-five percent (25%) on each of the first and second anniversaries of achievement of the corresponding Performance Milestone.

Each share is represented by a Restricted Stock Unit ("RSU"). One-third (1/3) of the total RSUs will vest on each of the first three (3) anniversaries of the Vesting Commencement Date (2/1/2026), provided that the Reporting Person continues to serve through each such vesting date.

Each share is represented by a Performance-based Restricted Stock Unit ("PSU").

Grant of 7,413 PSUs, each of which represents a contingent right to receive one share of common stock of ATEN, with vesting subject to the achievement of specified levels of the volume weighted average closing prices of a share of ATEN common stock during any one hundred (100) day trading period between February 12, 2026 and February 12, 2030 (each, a "Performance Milestone"). Upon achievement of a Performance Milestone, vesting is subject to continued employment with the Company through the applicable vesting date, the first fifty percent ( 50%) of which will occur within thirty (30) days of achievment of the applicable milestone and the balance to vest twenty-five percent (25%) on each of the first and second anniversaries of achievement of the corresponding Performance Milestone.

The sales reported on this Form 4 were effected pursuant to a Rule 10b5-1 trading plan adopted by the Reporting Person on September 12, 2025.

This is the weighted average price of the shares sold, which ranged from $20.18 to $21.11 per share. Upon request by the Commission staff, the Issuer, or a security holder of the Issuer, the Reporting Person will provide full information regarding the number of shares sold at each separate price within the range set forth in this Form 4.

Each share is represented by a Restricted Stock Unit ("RSU"). One-third (1/3) of the total RSUs will vest on each of the first three (3) anniversaries of the Vesting Commencement Date (2/1/2026), provided that the Reporting Person continues to serve through each such vesting date.

Each share is represented by a Restricted Stock Unit ("RSU"). One-third (1/3) of the total RSUs will vest on each of the first three (3) anniversaries of the Vesting Commencement Date (2/1/2026), provided that the Reporting Person continues to serve through each such vesting date.

Each share is represented by a Restricted Stock Unit ("RSU"). One-third (1/3) of the total RSUs will vest on each of the first three (3) anniversaries of the Vesting Commencement Date (2/1/2026), provided that the Reporting Person continues to serve through each such vesting date.

The sales reported on this Form 4 were effected pursuant to a Rule 10b5-1 trading plan adopted by the Reporting Person on September 12, 2025.

This is the weighted average price of the shares sold, which ranged from $20.51 to $21.10 per share. Upon request by the Commission staff, the Issuer, or a security holder of the Issuer, the Reporting Person will provide full information regarding the number of shares sold at each separate price within the range set forth in this Form 4.

Shares automatically withheld, on a non-discretionary basis, for tax purposes related to performance-based restricted stock units granted on January 25, 2022, which vested on February 10, 2026.

Shares automatically withheld, on a non-discretionary basis, for tax purposes related to performance-based restricted stock units granted on July, 1 2022, which vested on February 10, 2026.

Shares automatically withheld, on a non-discretionary basis, for tax purposes related to restricted stock units granted on February 21, 2023, January 30, 2024 and February 6, 2025, each of which vested on February 1, 2026.

Shares automatically withheld, on a non-discretionary basis, for tax purposes related to restricted stock units granted on February 21, 2023, January 30, 2024 and February 6, 2025, each of which vested on February 1, 2026.

Shares automatically withheld, on a non-discretionary basis, for tax purposes related to performance-based restricted stock units granted on February 21, 2023, which vested on January 31, 2026.

Shares automatically withheld, on a non-discretionary basis, for tax purposes related to performance-based restricted stock units granted on February 21, 2023, which vested on January 31, 2026.

Shares automatically withheld, on a non-discretionary basis, for tax purposes related to a January 30, 2024 performance restricted stock unit grant that vested on January 15, 2026.

Shares automatically withheld, on a non-discretionary basis, for tax purposes related to a January 30, 2024 performance restricted stock unit grant that vested on January 15, 2026.

Shares automatically withheld, on a non-discretionary basis, for tax purposes related to a January 30, 2024 restricted stock unit grant that vested on December 13, 2025.

Shares automatically withheld, on a non-discretionary basis, for tax purposes related to a January 30, 2024 restricted stock unit grant that vested on December 13, 2025.

Represents a bona fide gift by Reporting Person to a tax-exempt public charity under Section 501(c)(3) of the Internal Revenue Code.

Includes an aggregate of 1,437 shares acquired by the Reporting Person on May 31, 2025 and November 30, 2025 pursuant to the Issuer's Employee Stock Purchase Plan.

Each share is represented by a Performance-based Restricted Stock Unit ("PSU").

Grant of 13,706 PSUs, each of which represents a contingent right to receive one share of common stock of ATEN, with vesting subject to the achievement of a specified level of the volume weighted average closing prices of a share of ATEN common stock during any one hundred (100) day period between September 30, 2025 and September 30, 2029 (the "Performance Milestone"). Upon achievement of the Performance Milestone, vesting is subject to continued employment with the Company through the applicable vesting date, which occurs in three installments, with the vesting of the first fifty percent (50%) to occur within thirty (30) days of achievement of the Performance Milestone and an additional twenty-five percent (25%) on each of the first and second anniversaries of the date of achievement of the Performance Milestone.