GPT-5.6 becomes the default model in Microsoft 365 Copilot

OpenAI·medium signal

OpenAI confirmed GPT-5.6 is now the preferred model powering Microsoft 365 Copilot, landing within a day of the ChatGPT Work launch. The move keeps Microsoft's agent surface on OpenAI's frontier tier at the exact moment OpenAI ships a competing agentic workspace, an unusually direct overlap between partner and product. Builders on Copilot extensibility should expect tool-calling and long-horizon task behavior to shift under them without an opt-in.