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): January 23, 2015

GFI GROUP INC.

(Exact name of registrant as specified in its charter)

Registrant’s telephone number, including area code: (212) 968-4100

Not Applicable

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:

x Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425)

o Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12)

o Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b))

o Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))

Item 8.01. Other Events.

On January 23, 2015, GFI Group Inc. (“GFI” or the “Company”) issued a press release announcing that the special meeting of GFI stockholders (the “Special Meeting”) scheduled for January 27, 2015 is being postponed to January 30, 2015.  The Special Meeting is being postponed in order to provide GFI stockholders with additional disclosures and information to be contained in a supplement to the proxy statement/prospectus that GFI and CME Group Inc. (“CME”) intend to file with the Securities and Exchange Commission (the “SEC”).  A copy of the press release is attached hereto as Exhibit 99.1 and is incorporated herein by reference.

Important Information for Investors and Stockholders

In connection with the proposed transaction between the Company and CME, on December 24, 2014, the SEC declared effective the registration statement on Form S-4 that included a definitive proxy statement of the Company that also constituted a definitive prospectus of CME. On December 24, 2014, the Company commenced mailing the definitive proxy statement/prospectus to stockholders of the Company. GFI and CME intend to issue a supplement to the definitive proxy statement/prospectus on Form 424(b)(3) with the SEC, which will be mailed to stockholders of GFI. INVESTORS AND SECURITY HOLDERS OF THE COMPANY ARE URGED TO READ THE DEFINITIVE PROXY STATEMENT/PROSPECTUS (INCLUDING ALL AMENDMENTS AND SUPPLEMENTS THERETO) AND OTHER DOCUMENTS FILED WITH THE SEC, CAREFULLY AND IN THEIR ENTIRETY BECAUSE THEY CONTAIN OR WILL CONTAIN IMPORTANT INFORMATION. Investors and security holders may obtain free copies of the registration statement and the definitive proxy statement/prospectus and other documents filed with the SEC by CME and the Company through the website maintained by the SEC at http://www.sec.gov or at the SEC public reference room at 100 F Street N.E., Room 1580, Washington, D.C. 20549. Please call the SEC at (800) 732-0330 or visit the SEC’s website for further information on its public reference room. Copies of the documents filed with the SEC by the Company are available free of charge on the Company’s website at http://www.gfigroup.com or by contacting the Company’s Investor Relations Department at (212) 968-6905. Copies of the documents filed with the SEC by CME will be available free of charge on CME’s website at http://www.cmegroup.com or by contacting CME’s Investor Relations Department at (312) 930-8491.

Participants in the Solicitation for the Proposed Merger Between the Company and CME

The Company and its directors, executive officers and certain of its employees may be considered participants in the solicitation of proxies in connection with the proposed transactions involving the Company and CME. Investors and security holders may obtain more detailed information regarding the names, affiliates and interests of the Company’s directors and executive officers by reading the Company’s Annual Report on Form 10-K for the year ended December 31, 2013, which was filed with the SEC on March 13, 2014, its proxy statement for its 2014 annual meeting of stockholders, which was filed with the SEC on April 22, 2014, and its Current Report on Form 8-K filed with the SEC on July 25, 2014. These documents can be obtained free of charge from the sources indicated above. Additional information regarding the participants in the proxy solicitations and a description of their direct and indirect interests, by security holdings or otherwise, is or will be contained in the proxy statement/prospectus and other relevant materials filed with the SEC. This Current Report on Form 8-K shall not constitute an offer to sell or the solicitation of an offer to buy any securities, nor shall there be any sale of securities in any jurisdiction in which such offer, solicitation or sale would be unlawful prior to appropriate registration or qualification under the securities laws of such jurisdiction. No offering of securities shall be made except by means of a prospectus meeting the requirements of Section 10 of the Securities Act of 1933, as amended.

Cautionary Statement Regarding Forward-Looking Statements

Certain matters discussed in this Current Report on Form 8-K and the exhibits incorporated herein contain forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995. These forward-looking statements include, but are not limited to (i) plans, objectives, expectations and intentions; (ii) other statements contained in this communication that are not historical facts; and (iii) other statements identified by words such as “anticipate,” “believe,” “estimate,” “may,” “might,” “intend,” “expect” and similar expressions. Actual results, performance or achievements could differ materially from those contemplated, expressed or implied by the forward-looking statements contained herein. These forward-looking statements are based largely on the expectations of the Company and are subject to a number of risks and uncertainties. These include, but are not limited to, risks and uncertainties associated with: the occurrence of any event, change or other circumstances that could give rise to the termination of the definitive agreements involving the Company and CME; the inability to complete the proposed merger involving the Company and CME due to the failure to obtain the required stockholder approval; the inability to satisfy the other conditions to the closing of the proposed merger involving the Company and CME or the tender offer by BGC Partners, Inc. (“BGC”), including without limitation the receipt of necessary governmental or regulatory approvals required to complete either transaction; the risk that either transaction disrupts current

2

plans and operations and/or increases operating costs and the potential difficulties in customer loss and employee retention as a result of the announcement and consummation of either transaction; the outcome of any legal proceedings that may be instituted against the Company, CME, BGC or others following announcement of either transaction; economic, political and market factors affecting trading volumes; securities prices or demand for the Company’s brokerage services; competition from current and new competitors; the Company’s ability to attract and retain key personnel, including highly-qualified brokerage personnel; the Company’s ability to identify and develop new products and markets; changes in laws and regulations governing the Company’s business and operations or permissible activities; the Company’s ability to manage its international operations; financial difficulties experienced by the Company’s customers or key participants in the markets in which the Company focuses its services; the Company’s ability to keep up with technological changes; and uncertainties relating to litigation and the Company’s ability to assess and integrate acquisition prospects. Further information about factors that could affect the financial and other results of the Company is included in its filings with the SEC. The Company undertakes no obligation to publicly update or revise any forward-looking statements, whether as a result of new information, future events or otherwise.

These forward-looking statements speak only as of the date hereof. Except for the ongoing obligations of the Company to disclose material information under the federal securities laws, the Company undertakes no obligation to revise or update publicly any forward-looking statement, except as required by law. Other factors that may impact the forward-looking statements are described in the Company’s annual report on Form 10-K for the fiscal year ended December 31, 2013 and Forms 10-Q. For additional information on the Company, please visit the Company’s website at http://www.gfigroup.com.

3

Item 9.01. Financial Statements and Exhibits.

(d) Exhibits

4

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 hereunto duly authorized.

5

EXHIBIT INDEX

6