GPT-5.6 Becomes the Default Model in Microsoft 365 Copilot

OpenAI has confirmed that GPT-5.6 is now the preferred and default model powering Microsoft 365 Copilot, replacing its predecessor across Word, Excel, Teams, and other M365 surfaces. This signals the speed at which OpenAI is deploying frontier model iterations into enterprise products at massive scale, compressing the gap between research release and production deployment. For developers building on the Microsoft 365 ecosystem or Copilot extensibility APIs, this means the underlying reasoning and tool-use capabilities available to their plugins and agents have materially improved. It also sets a precedent for how the Sol/Terra/Luna tiers may be routed in enterprise contexts — with Luna or Terra likely serving high-volume Copilot tasks and Sol reserved for complex workflows. Developers integrating with M365 Copilot should audit their prompts and tool schemas against the new model's behavior.