Sec Form 4 Filing - Bucci Sam @ Ribbon Communications Inc. - 2026-04-17

FORM 4 Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934, Section 17(a) of the Public Utility Holding Company Act of 1935 or Section 30(h) of the Investment Company Act of 1940

OMB APPROVAL OMB Number: 3235-0287 Expires: November 30, 2011 Estimated average burden hours per response... 0.5

1. Name and Address of Reporting Person Bucci Sam 2. Issuer Name and Ticker or Trading Symbol Ribbon Communications Inc. [ RBBN] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) _____ Director _____ 10% Owner X __ Officer (give title below) _____ Other (specify below) EVP, Chief Operating Officer (Last) (First) (Middle) 6500 CHASE OAKS BLVD., SUITE 100 3. Date of Earliest Transaction (MM/DD/YY) 04/17/2026 (Street) PLANO, TX75023 4. If Amendment, Date Original Filed (MM/DD/YY) 6. Individual or Joint/Group Filing (Check Applicable Line) __ X __ Form filed by One Reporting Person _____ Form filed by More than One Reporting Person (City) (State) (Zip)

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned 1.Title of Security (Instr. 3) 2. Transaction Date (MM/DD/YY) 2A. Deemed Execution Date, if any (MM/DD/YY) 3. Transaction Code (Instr. 8) 4. Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5) 5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4) 6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4) 7. Nature of Indirect Beneficial Ownership (Instr. 4) Code V Amount (A) or (D) Price Common Stock 04/17/2026 M 25,815 A 474,626 D Common Stock 04/17/2026 F 13,818 D $ 2.71 ( 2 ) 460,808 D Common Stock 04/17/2026 M 42,753 A 503,561 D Common Stock 04/17/2026 F 22,884 D $ 2.71 ( 2 ) 480,677 D Common Stock 04/17/2026 M 80,546 A 561,223 D Common Stock 04/17/2026 F 43,116 D $ 2.71 ( 2 ) 518,107 D Common Stock 05/15/2026 M 38,578 A 556,685 D Common Stock 05/15/2026 F 20,650 D $ 2.63 ( 2 ) 536,035 D Common Stock 05/15/2026 M 52,743 A 588,778 D Common Stock 05/15/2026 F 28,233 D $ 2.63 ( 2 ) 560,545 D Common Stock 05/15/2026 M 83,335 A 643,880 D Common Stock 05/15/2026 F 44,609 D $ 2.63 ( 2 ) 599,271 D

Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned ( e.g. , puts, calls, warrants, options, convertible securities) 1. Title of Derivative Security (Instr. 3) 2. Conversion or Exercise Price of Derivative Security 3. Transaction Date (MM/DD/YY) 3A. Deemed Execution Date, if any (MM/DD/YY) 4. Transaction Code (Instr. 8) 5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4, and 5) 6. Date Exercisable and Expiration Date (MM/DD/YY) 7. Title and Amount of Underlying Securities (Instr. 3 and 4) 8. Price of Derivative Security (Instr. 5) 9. Number of Derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4) 10. Ownership Form of Derivative Security: Direct (D) or Indirect (I) (Instr. 4) 11. Nature of Indirect Beneficial Ownership (Instr. 4) Code V (A) (D) Date Exercisable Expiration Date Title Amount or Number of Shares Restricted Share Units (RSUs) ( 1 ) 04/17/2026 M 25,815 ( 3 ) ( 3 ) Common Stock 25,815 $ 0 0 ( 3 ) D Performance Share Units (PSUs) ( 1 ) 04/17/2026 M 42,753 ( 4 ) ( 4 ) Common Stock 42,753 $ 0 0 ( 4 ) D PSUs ( 1 ) 04/17/2026 M 80,546 ( 5 ) ( 5 ) Common Stock 80,546 $ 0 0 ( 5 ) D PSUs ( 1 ) 05/15/2026 M 38,578 ( 6 ) ( 6 ) Common Stock 38,578 $ 0 0 ( 6 ) D RSUs ( 1 ) 05/15/2026 M 52,743 ( 7 ) ( 7 ) Common Stock 52,743 $ 0 52,742 ( 7 ) D RSUs ( 1 ) 05/15/2026 M 83,335 ( 8 ) ( 8 ) Common Stock 83,335 $ 0 166,665 ( 8 ) D

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other Bucci Sam 6500 CHASE OAKS BLVD. SUITE 100 PLANO, TX75023 EVP, Chief Operating Officer Signatures Patrick Macken, By POA from Sam Bucci, EVP, Chief Operating Offcer 05/19/2026 Signature of Reporting Person Date

Explanation of Responses:

( 1 )Each Restricted Share Unit (RSU) and Performance Share Unit (PSU) converts into common stock on a one-for-one basis. ( 2 )Reflects shares of Common Stock withheld by the Issuer to satisfy tax withholding obligations in connection with the vesting of the awards. ( 3 )The RSUs were granted on April 17, 2023 and are fully vested. ( 4 )The number of PSUs earned and issued upon vesting was determined based on goals (set by the Compensation Committee of the Issuer's Board of Directors (the "Compensation Committee") on an annual basis) for each of the three fiscal years ended December 31, 2025. Based on the Compensation Committee's determination of achievement of these pre-established financial goals, 32%, 70% and 36% of the shares subject to the 2023, 2024 and 2025 financial periods, respectively, were earned and vested on April 17, 2026. ( 5 )The number of PSUs earned and issued upon vesting was determined based on the Issuer's total shareholder return (TSR) compared to pre-established relative TSR goals, based on the TSR of a peer index of companies (set by the Compensation Committee at the time of grant) over the three fiscal years ended December 31, 2025. Based on the Compensation Committee's determination of achievement of the pre-established TSR goal, 130% of the shares subject to the PSU award were earned and vested on April 17, 2026. ( 6 )The number of PSUs earned and issued upon vesting was determined based on goals (set by the Compensation Committee on an annual basis) for each of the two fiscal years ended December 31, 2025. Based on the Compensation Committee's determination of achievement of these pre-established financial goals, 70% and 36% of the shares subject to the 2024 and 2025 financial periods, respectively, were earned and vested on May 15, 2026. ( 7 )The RSUs were granted on May 15, 2025 and vested as to one-half on May 15, 2026; the remaining one-half of the RSUs will vest in two equal semi-annual installments thereafter through May 15, 2027. ( 8 )The RSUs were granted on May 15, 2025 and vested as to one-third on May 15, 2026; the remaining two-thirds of the RSUs will vest in four equal semi-annual installments thereafter through May 15, 2028.

Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.

* If the form is filed by more than one reporting person, see Instruction 4(b)(v).

** Intentional misstatements or omissions of facts constitute Federal Criminal Violations. See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).

Note: File three copies of this Form, one of which must be manually signed. If space is insufficient, see Instruction 6 for procedure.
Persons who respond to the collection of information contained in this form are not required to respond unless the form displays a currently valid OMB Number.