Weil advised Microsoft Corporation on the UK Competition and Markets Authority (CMA) investigation into Microsoft’s partnership with OpenAI. 

The CMA commenced its investigation on December 8, 2023 following the dismissal and re-hiring of Sam Altman as CEO of OpenAI in November 2023. As part of a pre-notification process lasting almost 15 months, the CMA investigated the partnership in detail under its merger control powers to determine whether Microsoft had increased its level of control over OpenAI and, if so, whether competition concerns arose as a result. The CMA concluded on March 5, 2025 that it did not have jurisdiction to review the partnership.

The Weil team, working closely with Microsoft’s legal team, was led by London Antitrust partner Jenine Hulsmann, counsel Lucy Chambers and Chris Chapman and also included associates Robert Eyres, Patrick May, Hannah Bannister and Venetia Hudd.