Regulation FD Disclosure (Form 8-K)

Omnicom Group Inc. ("Omnicom," the "Company," "we," "our" or "us") is hosting an Investor Day on March 12, 2026 to present the Company's growth strategy following the acquisition of The Interpublic Group of Companies, Inc. ("Interpublic"). The strategy is anchored in the Company's competitive advantages and supported by a clear financial framework designed to deliver long-term, sustainable growth.

Executives participating include: John Wren, Chairman and Chief Executive Officer; Phil Angelastro, Executive Vice President and Chief Financial Officer; Daryl Simm, Co-Presidentand Co-ChiefOperating Officer; George Manas, Chief Growth and Solutions Officer; Paolo Yuvienco, Chief Technology Officer; Jacki Kelley, Chief Client & Business Officer, and operational leaders across media, creative, consulting, and product.

At the Investor Day, the Company is also providing a financial update, which includes an outlook for the year ending December 31, 2026:

The information furnished pursuant to Item 7.01 shall not be deemed to be "filed" for purposes of Section 18 of the Securities Exchange Act of 1934, as amended (the "Exchange Act"), or otherwise subject to the liabilities of that section, nor shall such information be deemed incorporated by reference in any filing under the Securities Act of 1933, as amended, or the Exchange Act, except as shall be expressly set forth by specific reference in such a filing.

Non-GAAPFinancial Measures

We present financial measures determined in accordance with generally accepted accounting principles in the United States ("GAAP") and adjustments to the GAAP presentation ("Non-GAAP"),which we believe are meaningful for understanding our performance. We believe these measures are useful in evaluating the impact of certain items on operating performance and allow for comparability between reporting periods. We define EBITA as earnings before interest, taxes, and amortization of acquired intangible assets and internally developed strategic platform assets. EBITDA is defined as earnings before interest, taxes, depreciation and amortization of intangible assets, and EBITA margin is defined as EBITA divided by revenue. We use EBITA, EBITDA and EBITA margin as additional operating performance measures, which exclude the non-cashamortization expense of acquired intangible assets and internally developed strategic platform assets. We also use Adjusted EBITDA, Adjusted Net Income - Omnicom Group Inc. and Adjusted Net Income per share - Omnicom Group Inc. - Diluted as additional operating performance measures. Non-GAAPfinancial measures should not be considered in isolation from, or as a substitute for, financial information presented in accordance with GAAP. Non-GAAPfinancial measures as reported by us may not be comparable to similarly titled amounts reported by other companies. We are not able to forecast Net Income on a forward-looking basis without unreasonable efforts due to the high variability and difficulty in predicting certain items that affect Net Income.