Company: CIO
Filing Date: 2025-07-24
Form Type: DEFA14A
Source: 0001193125-25-163769
Chunk: 0

Company: City Office REIT, Inc.
Filing Date: 2025-07-24
Form: DEFA14A
Chunk 0
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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): July 23, 2025 City Office REIT, Inc. (Exact Name of Registrant as Specified in Its Charter)

| Maryland                     |     | 001-36409   |     | 98-1141883         |
| (State or other jurisdiction 
 of incorporation)            |     | -Commission 
 File Number |     | -I.R.S. Employer   
 Identification No. |

| 666 Burrard Street, Suite 3210,          |     |           |
| Vancouver, British Columbia              |     | V6C 2X8   |
| (Address of principal executive offices) |     | -Zip Code |

(604) 806-3366 (Registrant’s telephone number, including area code) Not Applicable (Former name or former address, if changed since last report) Check the appropriate box below if the Form 8-Kfiling is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions ( seeGeneral Instruction A.2. below):

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

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

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

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

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

| Title of Each Class                                                              |     | Trading 
 Symbols |     | Name of Each Exchange   
 on Which Registered     |
| Common Stock, $0.01 par value                                                    |     | CIO     |     | New York Stock Exchange |
| 6.625% Series A Cumulative Redeemable Preferred Stock, $0.01 par value per share |     | CIO.PrA |     | New York Stock Exchange |

Indicate by check mark whether the registrant is an emerging growth company as