UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 10-K

For the fiscal year ended December 31, 2015

or

For the transition period from                      to                     

Commission file number                     

333-166711-02

(Commission File Number of issuing entity)

0001556811

(Central Index Key Number of issuing entity)

Citigroup Commercial Mortgage Trust 2012-GC8

(Exact name of issuing entity as specified in its charter)

333-166711

(Commission File Number of depositor)

0001258361

(Central Index Key Number of depositor)

Citigroup Commercial Mortgage Securities Inc.

(Exact name of depositor as specified in its charter)

Citigroup Global Markets Realty Corp.

(Central Index Key Number: 0001541001)

Goldman Sachs Mortgage Company

(Central Index Key Number: 0001541502)

Natixis Real Estate Capital LLC

(Central Index Key Number: 0001542256)

(Exact name of sponsor as specified in its charter)

c/o Citibank, N.A.

388 Greenwich Street, 14^th Floor

New York, New York 10013

(Address of principal executive offices of issuing entity)

(212) 816-5614

Registrant’s telephone number, including area code

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

None

Securities registered pursuant to section 12(g) of the Act:

None

Indicate by check mark if the registrant is a well-known seasoned issuer, as defined in Rule 405 of the Securities Act.    ¨   Yes    x  No

Indicate by check mark if the registrant is not required to file reports pursuant to Section 13 or Section 15(d) of the Act.    ¨  Yes    x  No

Indicate by check mark whether the registrant (1) has filed all reports required to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during the preceding 12 months (or for such shorter period that the registrant was required to file such reports), and (2) has been subject to such filing requirements for the past 90 days.    x  Yes    ¨  No

Indicate by check mark whether the registrant has submitted electronically and posted on its corporate Web site, if any, every Interactive Data File required to be submitted and posted pursuant to Rule 405 of Regulation S-T (§ 232.405 of this chapter) during the preceding 12 months (or for such shorter period that the registrant was required to submit and post such files).

Not Applicable

Indicate by check mark if disclosure of delinquent filers pursuant to Item 405 of Regulation S-K (§ 229.405 of this chapter) is not contained herein, and will not be contained, to the best of registrant’s knowledge, in definitive proxy or information statements incorporated by reference in Part III of this Form 10-K or any amendment to this Form 10-K.

Not Applicable

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, or a smaller reporting company. See the definitions of “large accelerated filer,” “accelerated filer” and “smaller reporting company” in Rule 12b-2 of the Exchange Act.

Indicate by check mark whether the registrant is a shell company (as defined in Rule 12b-2 of the Act).    ¨  Yes     x  No

State the aggregate market value of the voting and non-voting common equity held by non-affiliates computed by reference to the price at which the common equity was last sold, or the average bid and asked price of such common equity, as of the last business day of the registrant’s most recently completed second fiscal quarter.

Not Applicable

Indicate by check mark whether the registrant has filed all documents and reports required to be filed by Section 12, 13 or 15(d) of the Securities Exchange Act of 1934 subsequent to the distribution of securities under a plan confirmed by a court.

Not Applicable

Indicate the number of shares outstanding of each of the registrant’s classes of common stock, as of the latest practicable date.

Not Applicable

DOCUMENTS INCORPORATED BY REFERENCE

List hereunder the following documents if incorporated by reference and the Part of the Form 10-K (e.g., Part I, Part II, etc.) into which the document is incorporated: (1) Any annual report to security holders; (2) Any proxy or information statement; and (3) Any prospectus filed pursuant to Rule 424(b) or (c) under the Securities Act of 1933. The listed documents should be clearly described for identification purposes (e.g., annual report to security holders for fiscal year ended December 24, 1980).

See Item 15.

PART I

Omitted.

Omitted.

None.

Omitted.

Omitted.

Not applicable.

PART II

Omitted.

Omitted.

Omitted.

Omitted.

Omitted.

Omitted.

Omitted.

None.

PART III

Omitted.

Omitted.

Omitted.

Omitted.

Omitted.

ADDITIONAL DISCLOSURE ITEMS REQUIRED BY GENERAL INSTRUCTION J(2)

Item 1112(b) of Regulation AB

The property securing the Miami Center mortgage loan constitutes a significant obligor within the meaning of Item 1101(k)(2) of Regulation AB and as disclosed in the Prospectus Supplement for Citigroup Commercial Mortgage Trust 2012-GC8 filed on September 24, 2012. In accordance with Item 1112(b) of Regulation AB, the most recent unaudited net operating income of the significant obligor was $13,688,159 for the twelve month period ended December 31, 2015.

Item 1114(b)(2) and Item 1115(b) of Regulation AB

No entity or group of affiliated entities provides any external credit enhancement, uses any derivative instruments or other support for the certificates within this transaction.

Item 1117 of Regulation AB

Disclosure from Citibank, N.A., as Certificate Administrator:

On June 18, 2014, a civil action was filed against Citibank, N.A. (“Citibank”) in the Supreme Court of the State of New York by a group of investors in 48 private-label RMBS trusts for which Citibank allegedly serves or did serve as trustee, asserting claims for purported violations of the Trust Indenture Act of 1939, breach of contract, breach of fiduciary duty and negligence based on Citibank’s alleged failure to perform its duties as trustee for the 48 RMBS trusts. On November 24, 2014, plaintiffs sought leave to withdraw this action. On the same day, a smaller subset of similar plaintiff investors in 27 private-label RMBS trusts for which Citibank allegedly serves or did serve as trustee, filed a new civil action against Citibank in the United States District Court for the Southern District of New York asserting similar claims as the prior action filed in state court. In January 2015, the court closed plaintiffs’ original state court action. Citibank’s motion to dismiss the federal complaint was fully briefed as of May 13, 2015. On September 8, 2015, the federal court dismissed all claims as to 24 of the 27 trusts and allowed certain of the claims to proceed as to the other three trusts. That case, involving the three remaining trusts, is pending.

On November 24, 2015, the same investors that brought the federal case brought a new civil action in the Supreme Court of the State of New York related to 25 private-label RMBS trusts for which Citibank allegedly serves or did serve as trustee. This case includes

the 24 trusts previously dismissed in the federal action, and one additional trust. The investors assert claims for breach of contract, breach of fiduciary duty, breach of duty to avoid conflicts of interest, and violation of New York’s Streit Act. Citibank filed a motion to dismiss this case on February 26, 2016.

On August 19, 2015, the Federal Deposit Insurance Corporation (FDIC) as Receiver for a financial institution filed a civil action against Citibank in the Southern District of New York. This action relates to one private-label RMBS trust for which Citibank formerly served as trustee. FDIC asserts claims for breach of contract, violation of the Streit Act, and violation of the Trust Indenture Act. Citibank is jointly briefing a motion to dismiss with The Bank of New York Mellon and U.S. Bank, entities that have also been sued by FDIC in their capacity as trustee, and whose cases are all in front of Judge Carter. Defendants’ joint motion to dismiss was fully briefed as of March 22, 2016.

There can be no assurances as to the outcome of litigation or the possible impact of litigation on the trustee or the RMBS trusts. However, Citibank denies liability and continues to vigorously defend against these litigations. Furthermore, neither the above-disclosed litigations nor any other pending legal proceeding involving Citibank will materially affect Citibank’s ability to perform its duties as Certificate Administrator under the Pooling and Servicing Agreement for this CMBS transaction.

Item 1119 of Regulation AB

Provided previously in the prospectus supplement of the Registrant relating to the issuing entity and filed on September 24, 2012 pursuant to Rule 424(b)(5) of the Securities Act of 1933, as amended.

Item 1122 of Regulation AB

The reports on assessment of compliance with servicing criteria for asset-backed securities and related attestation reports are attached hereto under Item 15.

Item 1123 of Regulation AB

The servicer compliance statements are attached hereto under Item 15.

PART IV

SIGNATURES

Pursuant to the requirements of Section 13 or 15(d) 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.

Date: March 30, 2016

Citigroup Commercial Mortgage Securities Inc.

(Depositor)

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