OpenAI announced that the new GPT-5.6 family will become the preferred model in Microsoft 365 Copilot, running across Word, Excel, PowerPoint, Copilot Chat, and Cowork for Microsoft 365 customers. The announcement landed two days after a report that Microsoft moved some prompts to its own MAI models. Microsoft will also access GPT-5.6 directly through the OpenAI API. OpenAI announced the change alongside the wider launch of GPT-5.6, a flagship series that arrives in three variants named Sol, Terra, and Luna. Sol, the flagship variant, costs $5 per million input tokens, and Chief Executive Sam Altman has claimed it is 54% more token efficient on coding tasks. OpenAI also claims Sol beats Anthropic's rival Fable 5 by 2.8 points on a closely watched coding benchmark. Two days earlier, it was reported that Microsoft had begun answering a share of Word and Excel prompts with its own MAI models, part of a broader industry push to rein in AI costs. Microsoft said it had nothing further to add when asked. The relationship has been loosening for more than a year; Microsoft, which has poured roughly $13 billion into OpenAI since 2019, lost its exclusive cloud provider status in January 2025 and gave up exclusive access to OpenAI's intellectual property in April.