Starting September 12, 2026, Microsoft began rolling Grok models from xAI into Microsoft 365 Copilot inside Word, Excel, and PowerPoint through the Microsoft Frontier Program, described as a focused release to gather customer feedback on common productivity scenarios. The rollout excludes Frontier customers in the EU, EFTA, and the United Kingdom during the preview period. IT administrators must explicitly enable Grok; it is off by default. When users choose Grok, their data is routed to SpaceXAI servers, and xAI has been added to Microsoft's online services sub-processor list because customer data may be processed by xAI when its models are used. Microsoft states it subjects third-party models to testing, safety validation, and Responsible AI reviews before making them available. Earlier in 2026, Grok 4.1 Fast was added to Copilot Studio in February as a preview for US-based makers, also off by default and requiring admin opt-in, designed for large context and deep tool use. Grok 4.6 became available in GitHub Copilot on August 14, 2026, accessible via model picker, Copilot CLI, and VS Code IDE. Microsoft 365 Copilot also allows users to replace the default OpenAI model with Anthropic's Claude on specific features, with the Researcher agent, which searches emails, files, chats, and the web, described as the clearest place to make that switch. Claude is off by default in the EU and UK and must be enabled by IT administrators there.