Filed Pursuant to Rule 424(b)(3)
Registration No. 333-259637

PROSPECTUS SUPPLEMENT NO. 8

(to Prospectus dated October 6, 2021)

GREENIDGE GENERATION HOLDINGS INC.

3,500,000 Shares of

Class A Common Stock

This prospectus supplement further supplements and updates the prospectus dated October 6, 2021 (as may be supplemented or amended from time to time, the “Prospectus”) relating to the resale of 3,500,000 shares of our Class A common stock, $0.0001 par value per share (“Class A common stock”). This prospectus supplement updates and supplements the information in the Prospectus and is not complete without, and may not be delivered or utilized except in combination with, the Prospectus, including any amendments or supplements thereto. This prospectus supplement should be read in conjunction with the Prospectus and if there is any inconsistency between the information in the Prospectus and this prospectus supplement, you should rely on the information in this prospectus supplement.

This prospectus supplement incorporates into the Prospectus the information contained in our attached:

Our Class A common stock is listed on the Nasdaq Global Select Market under the symbol “GREE”. On December 30, 2021, the closing price of our Class A common stock was $16.90.

See the section entitled “Risk Factors” beginning on page 17 of the Prospectus to read about factors you should consider before buying our securities.

Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or determined if this prospectus supplement or the accompanying Prospectus is truthful or complete. Any representation to the contrary is a criminal offense.

The date of this prospectus supplement is December 30, 2021.

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

Date of Report (Date of earliest event reported): December 28, 2021

GREENIDGE GENERATION HOLDINGS INC.

(Exact Name of Registrant as Specified in its Charter)

Registrant’s telephone number, including area code: (315) 536-2359

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 or Rule 12b-2 of the Securities Exchange Act of 1934:

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. ☐

On December 28, 2021, Greenidge Generation Holdings Inc. (the “Company”) determined to accelerate the vesting of restricted stock units (“RSUs”) granted to Jeffrey Kirt, originally vesting on March 8, 2022, such that the RSUs vested on December 28, 2021, subject to clawback and offset against any other amount due and payable to Mr. Kirt if the RSUs would not otherwise have vested on March 8, 2022 in accordance with the RSU Award Agreement, dated March 8, 2021, between Mr. Kirt and the Company.

Signature(s)

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, hereunto duly authorized.