GPT-5.6 becomes preferred model in Microsoft 365 Copilot

OpenAI announced during the GPT‑5.6 launch that GPT‑5.6 will be the “preferred model” powering Microsoft 365 Copilot across productivity apps including Word, Excel, PowerPoint, Copilot Chat and Cowork. OpenAI published a blog post saying GPT‑5.6 will support Microsoft users across the suite; Microsoft will serve the model natively in Copilot experiences and can also access it via the OpenAI API. The disclosure follows Bloomberg reporting that Microsoft has been increasing use of its own in‑house models (MAI) to cut costs, which sparked coverage questioning whether the two companies were drifting apart. OpenAI’s announcement frames the move as a continuation of the partnership, but it did not fully define what “preferred model” entails and does not appear to negate prior reports that Microsoft is also deploying its own models to reduce expenses.