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: December 8, 2015

CYRUSONE INC.

(Exact Name of Registrant as Specified in its Charter)

1649 West Frankford Road

Carrollton, TX 75007

(Address of Principal Executive Office)

Registrant’s telephone number, including area code: (972) 350-0060

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 (see General Instruction A.2. below):

o                 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 December 8, 2015, CyrusOne Inc. (“CyrusOne”) issued a press release announcing that a subsidiary of Cincinnati Bell Inc. (“Cincinnati Bell”) plans to sell 1,350,000 of its shares of CyrusOne’s common stock in an underwritten public offering. CyrusOne will not receive any proceeds from the offering. Closing of the offering is expected to occur on or about December 14, 2015, subject to customary closing conditions. The total number of shares of CyrusOne’s outstanding common stock will not change as a result of this offering.

A copy of the press release is furnished herewith as Exhibit 99.1.

ITEM 9.01 — FINANCIAL STATEMENTS AND EXHIBITS

(d) Exhibits

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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.

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EXHIBIT INDEX

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