Grayscale Sui Staking ETF (0002034012) (Filer)

UNITED STATES
SECURITIES AND EXCHANGE COMMISSION
WASHINGTON, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934

Grayscale Sui Staking ETF

(Exact name of Registrant as Specified in Its Charter)

(Former Name or Former Address, if Changed Since Last Report)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:

Securities registered pursuant to Section 12(b) of the Act:

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (§ 230.405 of this chapter) or Rule 12b-2 of the Securities Exchange Act of 1934 (§ 240.12b-2 of this chapter).

Emerging growth company ☒

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act. ☐

Capitalized terms used but not defined herein have the definitions given to them in the Trust's Registration Statement on Form S-1, as amended (File No. 333-291974).

Item 1.01. Entry into a Material Definitive Agreement.

Additional Custodian; Custody Services Agreement

On September 29, 2026, Grayscale Investments Sponsors, LLC, the sponsor (the “Sponsor”) of the Grayscale Sui Staking ETF (the “Trust”), on behalf of the Trust, and Anchorage Digital Bank N.A. (“Anchorage Digital”), a national trust bank chartered by the Office of the Comptroller of the Currency, entered into the Sixth Amendment (the “Anchorage Digital Amendment”) to the Master Custody Service Agreement, dated as of August 8, 2025 (as amended, the “Anchorage Digital Custodian Agreement”), pursuant to which the Trust became a party to the Anchorage Digital Custodian Agreement.

Pursuant to the Anchorage Digital Custody Agreement, Anchorage Digital will provide services related to the custody and safekeeping of a portion of the Trust’s SUI holdings.

The Sponsor intends to utilize Anchorage Digital’s services to custody a portion of the Trust’s SUI. The Trust’s existing custody arrangement with Coinbase Custody Trust Company, LLC is unaffected by the Trust’s entry into the Anchorage Digital Custodian Agreement, and Coinbase remains the Trust’s primary custodian. The Sponsor shall, in its sole discretion, determine the amounts held at either custodian as permitted by the Trust Agreement. At the current time, the Sponsor has not determined the total amount of the Trust’s SUI it will move to Anchorage Digital. The addition of Anchorage Digital reflects the Sponsor’s ongoing risk management approach as part of the Trust’s growing size. References to the “Custodian” in this prospectus refer to Coinbase Custody Trust Company, LLC, Anchorage Digital and/or other custodians, collectively or in their individual capacities, as the context may require.

With respect to the Trust’s SUI held by Anchorage Digital, upon Sponsor instruction, Anchorage Digital will withdraw from the Trust’s account maintained with Anchorage Digital the amount of SUI necessary to pay the Trust’s Sponsor's Fee and any Additional Trust Expenses, consistent with the procedures described on page 88 of the Trust's prospectus, dated April 16, 2026, under “Business—Expenses; Sales of SUI—Disposition of SUI.” Fees paid to the Additional Custodian are a Sponsor-paid Expense.

Under the Anchorage Digital Custodian Agreement, Anchorage Digital receives the Trust’s SUI for storage by generating private keys and their corresponding public keys, and retains custody of those private keys at all times. The hardware security module Anchorage Digital uses to safeguard such private keys is located in the United States.

In the event of a fork of the Sui blockchain, the Anchorage Digital Custody Agreement provides that Anchorage Digital may temporarily suspend services, and may, in its sole discretion, determine whether or not to support (or cease supporting) either branch of the forked protocol entirely, provided that Anchorage Digital shall use commercially reasonable efforts to avoid ceasing to support both branches of such forked protocol.

In addition, the Additional Custodian is required under the Anchorage Digital Custodian Agreement to maintain certain insurance coverage, which the Sponsor believes is industry standard, including commercial crime insurance or a fidelity bond with limits of not less than $100 million in the aggregate, covering theft of money or other property under the Additional Custodian’s case, custody or control, including digital assets held in cold storage. Shareholders cannot be assured that the Additional Custodian will maintain adequate insurance or that such coverage will cover losses with respect to the Trust’s SUI.

The foregoing description of the Anchorage Digital Custodian Agreement does not purport to be complete and is qualified in its entirety by reference to the full text of the Anchorage Digital Custodian Agreement and the Anchorage Digital Amendment, which are filed with this Current Report on Form 8-K as Exhibits 10.1 and 10.2, respectively.

Item 9.01. Financial Statements and Exhibits.

(d) Exhibits

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned thereunto duly authorized.

* The Registrant is a trust and the identified person signing this report is signing in their capacity as an authorized officer of Grayscale Investments Sponsors, LLC, the Sponsor of the Registrant.