Sec Form 4 Filing - FICHTHORN JOHN @ QUANTUM CORP /DE/ - 2026-06-01

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

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1. Name and Address of Reporting Person FICHTHORN JOHN 2. Issuer Name and Ticker or Trading Symbol QUANTUM CORP /DE/ [ QMCO] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) X __ Director X __ 10% Owner _____ Officer (give title below) _____ Other (specify below) (Last) (First) (Middle) C/O QUANTUM CORPORATION, 10770 E. BRIARWOOD AVE. 3. Date of Earliest Transaction (MM/DD/YY) 06/01/2026 (Street) CENTENNIAL, CO80112 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 06/04/2026 C( 1 )( 2 ) 11,020,645 A $ 5.194 11,020,645 ( 1 ) ( 2 ) I by Dialectic Technology SPV LLC ( 3 ) Common Stock 06/04/2026 A( 1 )( 2 ) 3,083,975 A $ 5.194 14,104,620 ( 1 ) ( 2 ) ( 4 ) I by Dialectic Technology SPV LLC ( 3 ) Common Stock 28,896 ( 5 ) 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 Warrant (right to buy) $ 5.194 ( 6 ) 06/01/2026( 6 ) J 105,911 ( 6 ) 06/01/2026( 6 ) 06/01/2031( 6 ) Common Stock 105,911 ( 6 ) ( 6 ) 105,911 ( 6 ) I by Dialectic Technology SPV LLC ( 3 ) Convertible Notes $ 5.194 ( 1 ) ( 2 ) 06/04/2026 C 57,241,228 ( 1 ) ( 2 ) 12/18/2025 ( 1 )( 2 ) Common Stock 11,020,645 ( 1 ) ( 2 ) ( 1 ) ( 3 ) 0 ( 1 ) ( 3 ) I by Dialectic Technology SPV LLC ( 3 )

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other FICHTHORN JOHN C/O QUANTUM CORPORATION 10770 E. BRIARWOOD AVE. CENTENNIAL, CO80112 X X Signatures Tara Ilges, attorney-in-fact for John A. Fichthorn 06/08/2026 Signature of Reporting Person Date

Explanation of Responses:

( 1 )On June 4, 2026 (the "Closing Date"), pursuant to a Conversion Agreement dated June 1, 2026 (the "Conversion Agreement"), by and among, among others, the Issuer and Dialectic (as defined below), Dialectic converted $57,241,228.00 of the previously issued 10.00% PIK senior secured convertible notes due 2028 (the "Convertible Notes"), consisting of the entire principal amount and all accrued and unpaid interest thereon, subject to certain conditions set forth in the Conversion Agreement (the "Conversion"). ( 2 )In connection with the Conversion, on the Closing Date, the Convertible Notes were cancelled, and the Issuer issued to Dialectic 11,020,645 shares of Common Stock (as defined below). ( 3 )These securities are held directly by Dialectic, a 10% holder of the Issuer, and indirectly by John Fichthorn. Mr. Fichthorn is the Manager of Dialectic Technology Manager LLC, the Manager of Dialectic. The Reporting Person disclaims beneficial ownership of these securities, except to the extent of the Reporting Person's pecuniary interest therein, if any. ( 4 )On the Closing Date, as consideration for the Conversion, the Issuer issued to Dialectic, (i) 3,083,975 additional shares of Common Stock (the "Consideration Shares"), which represents the quotient of (A) approximately $13.0 million, the present value of nominal PIK interest that would accrue on the Convertible Notes from the Closing Date to the maturity date thereof, discounted at a rate of 11%, plus (B) approximately $3.0 million, the Term Loan Deferred Cash Interest Amount (as defined in the Credit Agreement) owed to Dialectic, divided by $5.194. ( 5 )Includes 1,625 shares of Common Stock received by the Reporting Report as a result of a distribution of assets from a trust on June 1, 2026, which shares previously held indirectly by such trust were previously inadvertently omitted. ( 6 )On June 1, 2026 ("Issuance Date"), the Issuer issued to Dialectic Technology SPV LLC ("Dialectic") a warrant (the "Conversion Warrant") to purchase 105,911 (as may be adjusted pursuant to the Conversion Warrant) shares of common stock, par value $0.01 per share of the Issuer (the "Common Stock"), at an exercise price equal to $5.194 per share (as adjusted from time to time in accordance with the Conversion Warrant) on or after the Issuance Date and until the date that is five (5) years from the Issuance Date.

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