UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549





FORM 10-K





(Mark One)

|☒ | ANNUAL REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934
|- | ------------------------------------------------------------------------------------

For the fiscal year ended December 31, 2017

or



|☐ | TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934
|- | ----------------------------------------------------------------------------------------

For the transition period from
 to

333-189017-09

(Commission File Number of issuing entity)

0001643661

(Central Index Key Number of issuing entity)

Citigroup Commercial Mortgage Trust 2015-GC31

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

333-189017

(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)

Rialto Mortgage Finance, LLC

(Central Index Key Number: 0001592182)

RAIT Funding, LLC

(Central Index Key Number: 0001587045)

KGS-Alpha Real Estate Capital Markets, LLC

(Central Index Key Number: 0001499542)

(Exact name of sponsor as specified in its charter)



|                                                                    |  |                                     
|------------------------------------------------------------------- |  | ------------------------------------
|New York                                                            |  | 47-4463366
47-4475603
47-7148307    
|(State or other jurisdiction of
organization of the issuing entity) |  | (I.R.S. Employer
Identification No.)

c/o Citibank, N.A.

388 Greenwich Street, 14th 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    ☒  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    ☒  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.    ☒  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, a smaller reporting company,
or an emerging growth company. See the definitions of large accelerated filer, accelerated filer, smaller reporting company, and emerging growth company in Rule 12b-2 of the Exchange Act.



|                        |  |                                                  |  |                           |  |  
|----------------------- |  | ------------------------------------------------ |  | ------------------------- |  | -
|Large accelerated filer |  | ☐                                                |  | Accelerated filer         |  | ☐
|                        |  |                                                  | 
|Non-accelerated filer   |  | ☒  (Do not check if a smaller reporting company) |  | Smaller reporting company |  | ☐
|                        |  |                                                  | 
|                        |  |                                                  |  | 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.  ☐

Indicate by check mark whether the registrant is a shell company (as defined in Rule 12b-2 of the
Act).    ☐  Yes    ☒  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.









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PART I



|Item 1. | Business.
|------- | ---------

Omitted.



|Item 1A. | Risk Factors.
|-------- | -------------

Omitted.



|Item 1B. | Unresolved Staff Comments.
|-------- | --------------------------

None.



|Item 2. | Properties.
|------- | -----------

Omitted.



|Item 3. | Legal Proceedings.
|------- | ------------------

Omitted.



|Item 4. | Mine Safety Disclosures.
|------- | ------------------------

Not applicable.

PART II



|Item 5. | Market for Registrants Common Equity, Related Stockholder Matters and Issuer Purchases of Equity Securities.
|------- | -------------------------------------------------------------------------------------------------------------

Omitted.



|Item 6. | Selected Financial Data.
|------- | ------------------------

Omitted.



|Item 7. | Managements Discussion and Analysis of Financial Condition and Results of Operations.
|------- | --------------------------------------------------------------------------------------

Omitted.



---

|Item 7A. | Quantitative and Qualitative Disclosures About Market Risk.
|-------- | -----------------------------------------------------------

Omitted.



|Item 8. | Financial Statements and Supplementary Data.
|------- | --------------------------------------------

Omitted.



|Item 9. | Changes in and Disagreements With Accountants on Accounting and Financial Disclosure.
|------- | -------------------------------------------------------------------------------------

Omitted.



|Item 9A. | Controls and Procedures.
|-------- | ------------------------

Omitted.



|Item 9B. | Other Information.
|-------- | ------------------

None.

PART III



|Item 10. | Directors, Executive Officers and Corporate Governance.
|-------- | -------------------------------------------------------

Omitted.



|Item 11. | Executive Compensation.
|-------- | -----------------------

Omitted.



|Item 12. | Security Ownership of Certain Beneficial Owners and Management and Related Stockholder Matters.
|-------- | -----------------------------------------------------------------------------------------------

Omitted.



|Item 13. | Certain Relationships and Related Transactions, and Director Independence.
|-------- | --------------------------------------------------------------------------

Omitted.



|Item 14. | Principal Accounting Fees and Services.
|-------- | ---------------------------------------

Omitted.

ADDITIONAL DISCLOSURE ITEMS REQUIRED BY GENERAL INSTRUCTION J(2)

Item 1112(b) of Regulation AB

The property securing
the 135 South LaSalle 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 2015-GC31 filed on July 8, 2015.
With respect to the property securing the 135 South LaSalle mortgage loan, the most recent unaudited net operating income was $20,251,171 from January 1, 2017 through December 31, 2017.

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:

Citibank, N.A. (Citibank) is acting as the Certificate Administrator of this commercial mortgage-backed securities (CMBS) transaction.
In the ordinary course of business, Citibank is involved in a number of legal proceedings, including in connection with its role as trustee of certain residential mortgage-backed securities (RMBS) transactions. Certain of these Citibank
as trustee-related matters are disclosed herein.



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On June 18, 2014, a civil action was filed against 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 U.S. Trust Indenture Act of 1939, as amended (the Trust Indenture Act),
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. 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. Subsequently, plaintiffs voluntarily dismissed all claims with respect to two of the three trusts. On April 7, 2017, Citibank filed a motion for summary judgment.
Plaintiffs filed its consolidated opposition brief and cross motion for partial summary judgment on May 22, 2017. Briefing on those motions was completed on August 4, 2017.

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 (the Streit Act). Following oral argument on Citibanks motion to dismiss, plaintiffs filed an amended complaint on
August 5, 2016. On June 27, 2017, the state court issued a decision, dismissing the event of default claims, mortgage-file-related claims, the fiduciary duty claims, and the conflict of interest claims. The decision sustained certain
breach of contract claims including the claim alleging discovery of breaches of representations and warranties, a claim related to robo-signing, and the implied covenant of good faith claim. Citibank appealed the lower courts decision, and on
January 16, 2018, the Appellate Division, First Department, dismissed the claims related to robo-signing and the implied covenant of good faith, but allowed plaintiffs claim alleging discovery of breaches of representations and warranties
to proceed.

On August 19, 2015, the Federal Deposit Insurance Corporation (FDIC) as receiver for a failed 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 jointly briefed a motion to dismiss with The Bank of New York Mellon and U.S. Bank, N.A., entities that have also been sued by FDIC in their capacity as trustee, and these cases have all been
consolidated in front of Judge Carter. On September 30, 2016, the court granted Citibanks motion to dismiss the complaint without prejudice for lack of subject matter jurisdiction. On October 14, 2016, FDIC filed a motion for
reargument or relief from judgment from the courts dismissal order. On July 11, 2017, Judge Carter ruled on the motion for reconsideration regarding his dismissal of the action. He denied reconsideration of his decision on standing, but
granted leave to amend the complaint by October 9, 2017. The FDIC subsequently requested an extension of time to file its amended complaint, which was granted. The FDIC filed its amended complaint on December 8, 2017.

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.

Disclosure from Deutsche Bank Trust Company
Americas, as Trustee:

Deutsche Bank Trust Company Americas (DBTCA) and Deutsche Bank National Trust Company (DBNTC) have been
sued by investors in civil litigation concerning their role as trustees of certain residential mortgage-backed securities (RMBS) trusts.

On
June 18, 2014, a group of investors, including funds managed by Blackrock Advisors, LLC, PIMCO-Advisors, L.P., and others, filed a derivative action against DBNTC and DBTCA in New York State Supreme Court purportedly on behalf of and for the
benefit of 544 private-label RMBS trusts asserting claims for alleged violations of the U.S. Trust Indenture Act of 1939 (the Trust Indenture Act), breach of contract, breach of fiduciary duty and negligence based on DBNTC and
DBTCAs alleged failure to perform their duties as trustees for the trusts. Plaintiffs subsequently dismissed their state court complaint and filed a derivative and class action complaint in the U.S. District Court for the Southern District of
New York on behalf of and for the benefit of 564 private-label RMBS trusts, which substantially overlapped with the trusts at issue in the state court action. The complaint alleges that the trusts at issue have suffered total realized collateral
losses of U.S. $89.4 billion, but the complaint does not include a demand for money damages in a sum certain. DBNTC and DBTCA filed a motion to dismiss, and on January 19, 2016, the court partially granted the motion on procedural grounds:
as to the 500 trusts that are governed by pooling and servicing agreements, the court declined to exercise



---

jurisdiction. The court did not rule on substantive defenses asserted in the motion to dismiss. On March 22, 2016, plaintiffs filed an amended complaint in federal court. In the amended
complaint, in connection with 62 trusts governed by indenture agreements, plaintiffs assert claims for breach of contract, violation of the Trust Indenture Act, breach of fiduciary duty, and breach of duty to avoid conflicts of interest. The amended
complaint alleges that the trusts at issue have suffered total realized collateral losses of U.S. $9.8 billion, but the complaint does not include a demand for money damages in a sum certain. On July 15, 2016, DBNTC and DBTCA filed a
motion to dismiss the amended complaint. On January 23, 2017, the court granted in part and denied in part DBNTC and DBTCAs motion to dismiss. The court granted the motion to dismiss with respect to plaintiffs conflict-of-interest claim, thereby dismissing it, and denied the motion to dismiss with respect to plaintiffs breach of contract claim (except as noted below) and claim
for violation of the Trust Indenture Act, thereby allowing those claims to proceed. On January 26, 2017, the parties filed a joint stipulation and proposed order dismissing plaintiffs claim for breach of fiduciary duty. On
January 27, 2017, the court entered the parties joint stipulation and ordered that plaintiffs claim for breach of fiduciary duty be dismissed. On February 3, 2017, following a hearing concerning DBNTC and DBTCAs motion to
dismiss on February 2, 2017, the court issued a short form order dismissing (i) plaintiffs representation and warranty claims as to 21 trusts whose originators and/or sponsors had entered bankruptcy and the deadline for asserting
claims against such originators and/or sponsors had passed as of 2009 and (ii) plaintiffs claims to the extent they were premised upon any alleged pre-event of default duty to terminate servicers.
On March 27, 2017, DBNTC and DBTCA filed an answer to the amended complaint. On January 26, 2018, plaintiffs filed a motion for class certification. The parties are currently briefing the motion. Discovery is ongoing.

On March 25, 2016, the BlackRock plaintiffs filed a state court action against DBTCA in the Superior Court of California, Orange County with
respect to 513 trusts. On May 18, 2016, plaintiffs filed an amended complaint with respect to 465 trusts, and included DBNTC as an additional defendant. The amended complaint asserts three causes of action: breach of contract; breach of
fiduciary duty; and breach of the duty to avoid conflicts of interest. Plaintiffs purport to bring the action on behalf of themselves and all other current owners of certificates in the 465 trusts. The amended complaint alleges that the trusts at
issue have suffered total realized collateral losses of U.S. $75.7 billion, but does not include a demand for money damages in a sum certain. On August 22, 2016, DBNTC and DBTCA filed a demurrer as to plaintiffs breach of fiduciary
duty cause of action and breach of the duty to avoid conflicts of interest cause of action and motion to strike as to plaintiffs breach of contract cause of action. On October 18, 2016, the court granted DBNTC and DBTCAs demurrer,
providing plaintiffs with thirty days leave to amend, and denied DBNTC and DBTCAs motion to strike. Plaintiffs did not further amend their complaint and, on December 19, 2016, DBNTC and DBTCA filed an answer to the amended
complaint. On January 17, 2018, Plaintiffs filed a motion for class certification. The parties are currently briefing the motion. Discovery is ongoing.

On September 27, 2017, DBTCA was added as a defendant to a case brought by certain special purpose entities including Phoenix Light SF Limited in the
U.S. District Court for the Southern District of New York, in which the plaintiffs previously alleged incorrectly that DBNTC served as trustee for all 43 of the trusts at issue. On September 27, 2017, plaintiffs filed a third amended complaint
that names DBTCA as a defendant in addition to DBNTC. DBTCA serves as trustee for one of the 43 trusts at issue. DBNTC serves as trustee for the other 42 trusts at issue. Plaintiffs third amended complaint brings claims for violation of the
Trust Indenture Act; breach of contract; breach of fiduciary duty; negligence and gross negligence; violation of the New Yorks Streit Act (the Streit Act); and breach of the covenant of good faith. However, in the third amended
complaint, plaintiffs acknowledge that, before DBTCA was added to the case, the court dismissed plaintiffs Trust Indenture Act claims, negligence and gross negligence claims, Streit Act claims, claims for breach of the covenant of good faith,
and certain theories of plaintiffs breach of contract claims, and plaintiffs only include these claims to preserve any rights on appeal. Plaintiffs allege damages of hundreds of millions of dollars. On November 13, 2017, DBNTC
and DBTCA filed an answer to the third amended complaint. Discovery is ongoing.

On November 30, 2017, DBTCA was added as a defendant to a case
brought by Commerzbank AG (Commerzbank) in the U.S. District Court for the Southern District of New York, in which Commerzbank previously alleged incorrectly that DBNTC served as trustee for all 50 of the trusts at issue. On
November 30, 2017, Commerzbank filed a second amended complaint that names DBTCA as a defendant in addition to DBNTC. DBTCA serves as trustee for one of the 50 trusts at issue. DBNTC serves as trustee for the other 49 trusts at issue.
Commerzbanks second amended complaint brings claims for violation of the Trust Indenture Act; breach of contract; breach of fiduciary duty; negligence; violation of the Streit Act; and breach of the covenant of good faith. However, in the
second amended complaint, Commerzbank acknowledges that, before DBTCA was added to the case, the court dismissed Commerzbanks Trust Indenture Act claims for the trusts governed by pooling and servicing agreements, as well as its Streit Act
claims and claims for breach of the covenant of good faith, and Commerzbank only includes these claims to preserve any rights on appeal. The second amended complaint alleges that DBNTC and DBTCA caused Commerzbank to suffer hundreds of
millions of dollars in losses, but the complaint does not include a demand for money damages in a sum certain. On January 29, 2018, DBNTC and DBTCA filed an answer to the second amended complaint. Discovery is ongoing.



---

On December 30, 2015, IKB International, S.A. in Liquidation and IKB Deutsche Industriebank A.G.
(collectively, IKB), as an investor in 37 RMBS trusts, filed a summons with notice in the Supreme Court of the State of New York, New York County, against DBNTC and DBTCA as trustees of the trusts. On May 27, 2016, IKB served its
complaint asserting claims for breach of contract, breach of fiduciary duty, breach of duty to avoid conflicts of interest, violation of the Streit Act, violation of the Trust Indenture Act, violation of Regulation AB, and violation of
Section 9 of the Uniform Commercial Code. IKB alleges that DBNTC and DBTCA are liable for over U.S. $268 million in damages. On October 5, 2016, DBNTC and DBTCA, together with several other trustees defending lawsuits by IKB, filed a
joint motion to dismiss. On January 6, 2017, IKB filed a notice of discontinuance, voluntarily dismissing with prejudice all claims as to three trusts. As of January 17, 2017, DBNTC and DBTCAs motion to dismiss has been briefed and
is awaiting decision by the court. On June 20, 2017, the parties filed a stipulation, voluntarily dismissing with prejudice all claims as to four additional trusts. Certain limited discovery is permitted to go forward while the motion to
dismiss is pending.

It is DBTCAs belief that it has no pending legal proceedings (including, based on DBTCAs present evaluation, the
litigation disclosed in the foregoing paragraphs) that would materially affect its ability to perform its duties as Trustee under the Pooling and Servicing Agreement for this transaction.

Item 1119 of Regulation AB

Provided previously in
the prospectus supplement of the Registrant relating to the issuing entity and filed on July 8, 2015 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



|Item 15. | Exhibits, Financial Statement Schedules.
|-------- | ----------------------------------------



|(a) | List the following documents filed as a part of the report:
|--- | -----------------------------------------------------------



| | (1) | Not Applicable
| | --- | --------------



| | (2) | Not Applicable
| | --- | --------------



| | (3) | Exhibits listed below are either included or incorporated by reference as indicated below:
| | --- | ------------------------------------------------------------------------------------------



|               |  |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|-------------- |  | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
|Exhibit
Number |  | Description                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         
|4.1            |  | Pooling and Servicing Agreement, dated as of July 
1, 2015, by and among Citigroup Commercial Mortgage Securities, Inc., as depositor, Wells Fargo Bank, National Association, as master servicer, Torchlight Loan Services, LLC, as special servicer, Pentalpha Surveillance LLC, as operating advisor, Citibank,
 N.A., as certificate administrator, and Deutsche Bank Trust Company Americas, as trustee (filed as Exhibit 4.1 to the registrants Current Report on Form 8-K dated July 8, 2015, and filed by the
registrant on July 8, 2015 under Commission File No. 333-189017-09, and is incorporated by reference herein).



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|     |  |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              
|---- |  | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
|     | 
|4.2  |  | Pooling and Servicing Agreement, dated as of May 
1, 2015 (the GSMS 2015-GC30 PSA), by and among GS Mortgage Securities Corporation II, as depositor, Midland Loan Services, a Division of PNC Bank, National Association, as master servicer, Midland Loan Services, a Division of PNC Bank, National
 Association, as a special servicer, Trimont Real Estate Advisors, Inc., as operating advisor, U.S. Bank National Association, as trustee, and U.S. Bank National Association, as certificate administrator (filed as Exhibit 4.2 to the
registrants Current Report on Form 8-K dated July 8, 2015, and filed by the registrant on July 8, 2015 under Commission File
No. 333-189017-09, and is incorporated by reference herein)1.
|     | 
|4.3  |  | Pooling and Servicing Agreement, dated as of April 1, 
2015 (the CGCMT 2015-GC29 PSA), by and among Citigroup Commercial Mortgage Securities, Inc., as depositor, Midland Loan Services, a Division of PNC Bank, National Association, as master servicer, Midland 
Loan Services, a Division of PNC Bank, National Association, as special servicer, Situs Holdings, LLC, as operating advisor, Citibank, N.A., as certificate administrator, and Deutsche Bank Trust Company Americas, as 
trustee (filed as Exhibit 4.3 to the registrants Current Report on Form 8-K dated July 8, 2015, and filed by the registrant on July 8, 2015 under Commission File No. 333-189017-09, and is incorporated by reference herein)2.              
|     | 
|10.1 |  | Mortgage Loan Purchase Agreement, dated as of July 
1, 2015, between Citigroup Global Markets Realty Corp. and Citigroup Commercial Mortgage Securities Inc., pursuant to which Citigroup Global Markets Realty Corp. sold certain mortgage loans to Citigroup Commercial Mortgage Securities Inc. (filed as Exhibit
 10.1 to the registrants Current Report on Form 8-K dated July 8, 2015, and filed by the registrant on July 8, 2015 under Commission File No. 333-189017-09, and is incorporated by reference herein).                                                                                                                                                                                                                 
|     | 
|10.2 |  | Mortgage Loan Purchase Agreement, dated as of July 
1, 2015, between Goldman Sachs Mortgage Company and Citigroup Commercial Mortgage Securities Inc., pursuant to which Goldman Sachs Mortgage Company sold certain mortgage loans to Citigroup Commercial Mortgage Securities Inc. (filed as Exhibit 10.2 to the
registrants Current Report on Form 8-K dated July 8, 2015, and filed by the registrant on July 8, 2015 under Commission File
No. 333-189017-09, and is incorporated by reference herein).                                                                                                                                                                                                                                
|     | 
|10.3 |  | Mortgage Loan Purchase Agreement, dated as of July 
1, 2015, between Rialto Mortgage Finance, LLC and Citigroup Commercial Mortgage Securities Inc., pursuant to which Rialto Mortgage Finance, LLC sold certain mortgage loans to Citigroup Commercial Mortgage Securities Inc. (filed as Exhibit 10.3 to the registrants
Current Report on Form 8-K dated July 8, 2015, and filed by the registrant on July 8, 2015 under Commission File
No. 333-189017-09, and is incorporated by reference herein).                                                                                                                                                                                                                                    
|     | 
|10.4 |  | Mortgage Loan Purchase Agreement, dated as of July 
1, 2015, between RAIT Funding, LLC and Citigroup Commercial Mortgage Securities Inc., pursuant to which RAIT Funding, LLC sold certain mortgage loans to Citigroup Commercial Mortgage Securities Inc. (filed as Exhibit 10.4 to the registrants Current
 Report on Form 8-K dated July 8, 2015, and filed by the registrant on July 8, 2015 under Commission File
No. 333-189017-09, and is incorporated by reference herein).                                                                                                                                                                                                                                                         
|     | 
|10.5 |  | Mortgage Loan Purchase Agreement, dated as of July 
1, 2015, between KGS-Alpha Real Estate Capital Markets, LLC and Citigroup Commercial Mortgage Securities Inc., pursuant to which KGS-Alpha Real Estate Capital Markets, LLC sold
 certain mortgage loans to Citigroup Commercial Mortgage Securities Inc. (filed as Exhibit 10.5 to the registrants Current Report on Form 8-K dated July 8, 2015, and filed by the registrant on
July 8, 2015 under Commission File No. 333-189017-09, and is incorporated by reference herein).                                                                                                                                                                                                       



|1 | The Dallas Market Center mortgage loan, which represented approximately 9.9% of the initial pool balance of the issuing entity, is part of a loan combination comprised of the subject mortgage loan included in the
issuing entity and two pari passu companion loans that are held outside the issuing entity. The Dallas Market Center mortgage loan and the related companion loans are serviced pursuant to the GSMS 2015-GC30 PSA.
|- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

|2 | The Crowne Plaza Bloomington mortgage loan, which represented approximately 1.7% of the initial pool balance of the issuing entity, is part of a loan combination
comprised of the subject mortgage loan included in the issuing entity and one pari passu companion loan that is held outside the issuing entity. The Selig Office Portfolio mortgage loan, which represented approximately 9.95% of the initial pool
balance of the issuing entity, is part of a loan combination comprised of the subject mortgage loan included in the issuing entity and three pari passu companion loans that are held outside the issuing entity. The Crowne Plaza Bloomington mortgage
loan, the Selig Office Portfolio mortgage loan and each of the related companion loans are serviced pursuant to the CGCMT 2015-GC29 PSA.
|- | -----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------



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|      |  |                                                                                                                                                                                                                                                                                                                               
|----- |  | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
|31    |  | Rule 15d-14(d) Certification                                                                                                                                                                                                                                                                                                  
|      | 
|33    |  | Reports on assessment of compliance with servicing criteria for asset-backed securities.                                                                                                                                                                                                                                      
|      | 
|33.1  |  | Report on assessment of compliance with servicing criteria for asset-backed securities, Wells Fargo Bank, National Association, as master servicer                                                                                                                                                                            
|      | 
|33.2  |  | Report on assessment of compliance with servicing criteria for asset-backed securities, Torchlight Loan Services, LLC, as special servicer                                                                                                                                                                                    
|      | 
|33.3  |  | Report on assessment of compliance with servicing criteria for asset-backed securities, Pentalpha Surveillance LLC, as operating advisor                                                                                                                                                                                      
|      | 
|33.4  |  | Report on assessment of compliance with servicing criteria for asset-backed securities, Citibank, N.A., as certificate administrator                                                                                                                                                                                          
|      | 
|33.5  |  | Report on assessment of compliance with servicing criteria for asset-backed securities, Deutsche Bank Trust Company Americas, as custodian                                                                                                                                                                                    
|      | 
|33.6  |  | Report on assessment of compliance with servicing criteria for asset-backed securities, CoreLogic Commercial Real Estate Services, Inc., as servicing function participant                                                                                                                                                    
|      | 
|33.7  |  | Report on assessment of compliance with servicing criteria for asset-backed securities, National Tax Search, LLC, as servicing function participant                                                                                                                                                                           
|      | 
|33.8  |  | Report on assessment of compliance with servicing criteria for asset-backed securities, Midland Loan Services, a Division of PNC Bank, National Association, as master servicer for the Dallas Market Center mortgage
loan under the GSMS 2015-GC30 PSA                                                                       
|      | 
|33.9  |  | Report on assessment of compliance with servicing criteria for asset-backed securities, Midland Loan Services, a Division of PNC Bank, National Association, as special servicer for the Dallas Market Center mortgage
 loan under the GSMS 2015-GC30 PSA (see Exhibit 33.8)                                                  
|      | 
|33.10 |  | Report on assessment of compliance with servicing criteria for asset-backed securities, U.S. Bank National Association, as certificate administrator for the Dallas Market Center mortgage loan under the GSMS
 2015-GC30 PSA                                                                                                 
|      | 
|33.11 |  | Report on assessment of compliance with servicing criteria for asset-backed securities, U.S. Bank National Association, as custodian for the Dallas Market Center mortgage loan under the GSMS 2015-GC30 PSA (see
 exhibit 33.10)                                                                                             
|      | 
|33.12 |  | Report on assessment of compliance with servicing criteria for asset-backed securities, Trimont Real Estate Advisors, Inc., as operating advisor for the Dallas Market Center mortgage loan under the GSMS 2015-GC30
 PSA                                                                                                     
|      | 
|33.13 |  | Report on assessment of compliance with servicing criteria for asset-backed securities, Midland Loan Services, a Division of PNC Bank, National Association, as master servicer for the Crowne Plaza Bloomington
 mortgage loan and the Selig Office Portfolio mortgage loan under the CGCMT 2015-GC29 PSA (see Exhibit 33.8) 
|      | 
|33.14 |  | Report on assessment of compliance with servicing criteria for asset-backed securities, Midland Loan Services, a Division of PNC Bank, National Association, as special servicer for the Crowne Plaza Bloomington
 mortgage loan and the Selig Office Portfolio mortgage loan under the CGCMT 2015-GC29 PSA (see Exhibit 33.8)
|      | 
|33.15 |  | Report on assessment of compliance with servicing criteria for asset-backed securities, Citibank, N.A., as certificate administrator for the Crowne Plaza Bloomington mortgage loan and the Selig Office Portfolio
 mortgage loan under the CGCMT 2015-GC29 PSA (see Exhibit 33.4)                                            



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|      |  |                                                                                                                                                                                                                                                                                                                                           
|----- |  | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
|33.16 |  | Report on assessment of compliance with servicing criteria for asset-backed securities, Deutsche Bank Trust Company Americas, 
as custodian for the Crowne Plaza Bloomington mortgage loan and the Selig Office Portfolio mortgage loan under the CGCMT 2015-GC29 PSA (see 
Exhibit 33.5)                                                 
|      | 
|33.17 |  | Report on assessment of compliance with servicing criteria for asset-backed securities, Situs Holdings, LLC, as operating advisor for the Crowne Plaza Bloomington mortgage loan and the Selig Office Portfolio
 mortgage loan under the CGCMT 2015-GC29 PSA                                                                              
|      | 
|34    |  | Attestation reports on assessment of compliance with servicing criteria for asset-backed securities.                                                                                                                                                                                                                                      
|      | 
|34.1  |  | Attestation report on assessment of compliance with servicing criteria for asset-backed securities, Wells Fargo Bank, National Association, as master servicer                                                                                                                                                                            
|      | 
|34.2  |  | Attestation report on assessment of compliance with servicing criteria for asset-backed securities, Torchlight Loan Services, LLC, as special servicer                                                                                                                                                                                    
|      | 
|34.3  |  | Attestation report on assessment of compliance with servicing criteria for asset-backed securities, Pentalpha Surveillance LLC, as operating advisor                                                                                                                                                                                      
|      | 
|34.4  |  | Attestation report on assessment of compliance with servicing criteria for asset-backed securities, Citibank, N.A., as certificate administrator                                                                                                                                                                                          
|      | 
|34.5  |  | Attestation report on assessment of compliance with servicing criteria for asset-backed securities, Deutsche Bank Trust Company Americas, as custodian                                                                                                                                                                                    
|      | 
|34.6  |  | Attestation report on assessment of compliance with servicing criteria for asset-backed securities, CoreLogic Commercial Real Estate Services, Inc., as servicing function participant                                                                                                                                                    
|      | 
|34.7  |  | Attestation report on assessment of compliance with servicing criteria for asset-backed securities, National Tax Search, LLC, as servicing function participant                                                                                                                                                                           
|      | 
|34.8  |  | Attestation report on assessment of compliance with servicing criteria for asset-backed securities, Midland Loan Services, a Division of PNC Bank, National Association, as master servicer for the Dallas Market
 Center mortgage loan under the GSMS 2015-GC30 PSA                                                                      
|      | 
|34.9  |  | Attestation report on assessment of compliance with servicing criteria for asset-backed securities, Midland Loan Services, a Division of PNC Bank, National Association, as special servicer for the Dallas Market
 Center mortgage loan under the GSMS 2015-GC30 PSA (see Exhibit 34.8)                                                  
|      | 
|34.10 |  | Attestation report on assessment of compliance with servicing criteria for asset-backed securities, U.S. Bank National Association, as certificate administrator for the Dallas Market Center mortgage loan under
the GSMS 2015-GC30 PSA                                                                                                  
|      | 
|34.11 |  | Attestation report on assessment of compliance with servicing criteria for asset-backed securities, U.S. Bank National Association, as custodian for the Dallas Market Center mortgage loan under the GSMS 2015-GC30
 PSA (see exhibit 34.10)                                                                                             
|      | 
|34.12 |  | Attestation report on assessment of compliance with servicing criteria for asset-backed securities, Trimont Real Estate Advisors, Inc., as operating advisor for the Dallas Market Center mortgage loan under
 the GSMS 2015-GC30 PSA                                                                                                     
|      | 
|34.13 |  | Attestation report on assessment of compliance with servicing criteria for asset-backed securities, Midland Loan Services, a Division of PNC Bank, National Association, as master servicer for the Crowne Plaza
 Bloomington mortgage loan and the Selig Office Portfolio mortgage loan under the CGCMT 2015-GC29 PSA (see Exhibit 34.8) 
|      | 
|34.14 |  | Attestation report on assessment of compliance with servicing criteria for asset-backed securities, Midland Loan Services, a Division of PNC Bank, National Association, as special servicer for the Crowne Plaza
 Bloomington mortgage loan and the Selig Office Portfolio mortgage loan under the CGCMT 2015-GC29 PSA (see Exhibit 34.8)



---

|      |  |                                                                                                                                                                                                                                                                                                     
|----- |  | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
|      | 
|34.15 |  | Attestation report on assessment of compliance with 
servicing criteria for asset-backed securities, Citibank, N.A., as certificate administrator for the Crowne Plaza Bloomington mortgage loan and the Selig Office Portfolio mortgage loan under the CGCMT 2015-GC29 PSA (see Exhibit 34.4)      
|      | 
|34.16 |  | Attestation report on assessment of compliance with servicing criteria for asset-backed securities, Deutsche Bank Trust Company Americas, as custodian for the Crowne Plaza Bloomington mortgage loan and the Selig
 Office Portfolio mortgage loan under the CGCMT 2015-GC29 PSA (see Exhibit 34.5)
|      | 
|34.17 |  | Attestation report on assessment of compliance with servicing criteria for asset-backed securities, Situs Holdings, LLC, as operating advisor for the Crowne Plaza Bloomington mortgage loan and the Selig Office
 Portfolio mortgage loan under the CGCMT 2015-GC29 PSA                            
|      | 
|35    |  | Servicer compliance statements.3                                                                                                                                                                                                                                                                    
|      | 
|35.1  |  | Servicer compliance statement, Wells Fargo Bank, National Association, as master servicer                                                                                                                                                                                                           
|      | 
|35.2  |  | Servicer compliance statement, Torchlight Loan Services, LLC, as special servicer                                                                                                                                                                                                                   
|      | 
|35.3  |  | Servicer compliance statement, Citibank, N.A., as certificate administrator                                                                                                                                                                                                                         
|      | 
|35.4  |  | Servicer compliance statement, Midland Loan Services, a Division of PNC Bank, National Association, as master servicer for the Dallas Market Center mortgage loan under the GSMS 2015-GC30 PSA                                                                                                      
|      | 
|35.5  |  | Servicer compliance statement, Midland Loan Services, a Division of PNC Bank, National Association, as special servicer for the Dallas Market Center mortgage loan under the GSMS 2015-GC30 PSA (see exhibit 35.4)                                                                                  
|      | 
|35.6  |  | Servicer compliance statement, Midland Loan Services, a Division of PNC Bank, National Association, as master servicer for the Crowne Plaza Bloomington mortgage loan and the Selig Office Portfolio mortgage loan
 under the CGCMT 2015-GC29 PSA (see exhibit 35.4)                                
|      | 
|35.7  |  | Servicer compliance statement, Midland Loan Services, a Division of PNC Bank, National Association, as special servicer for the Crowne Plaza Bloomington mortgage loan and the Selig Office Portfolio mortgage
 loan under the CGCMT 2015-GC29 PSA (see exhibit 35.4)                               
|      | 
|35.8  |  | Servicer compliance statement, Citibank, N.A., as certificate administrator for the Crowne Plaza Bloomington mortgage loan and the Selig Office Portfolio mortgage loan under the CGCMT 2015-GC29 PSA (see Exhibit
 35.3)                                                                           



|(b) | The exhibits required to be filed by Registrant pursuant to Item 601 of Regulation S-K are listed above.
|--- | --------------------------------------------------------------------------------------------------------



|(c) | Not Applicable
|--- | --------------



|3 | This annual report on Form 10-K does not include the servicer compliance statement of U.S. Bank National Association, as certificate administrator for the Dallas Market Center mortgage loan under the GSMS 2015-GC30 PSA,
because U.S. Bank National Association is an unaffiliated party that services less than 10% of the pool assets of the issuing entity, and therefore is not a servicer that meets the criteria in Item 1108(a)(2)(i) through (iii) of
Regulation AB.
|- | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------



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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, 2018                         
|                                             
|Citigroup Commercial Mortgage Securities Inc.
|(Depositor)                                  
|                                             
|/s/ Paul Vanderslice                         
|Paul Vanderslice, President