GPT-5.6 Becomes the Preferred Model in Microsoft 365 Copilot on Launch Day
OpenAI's new flagship became Copilot's default-preferred model the same day it went GA — even as Microsoft quietly routes some Excel and Outlook prompts to its own MAI models.
OpenAI designated GPT-5.6 as the preferred model for Microsoft 365 Copilot on July 9, 2026, the same day the model family went generally available, according to a launch timeline compiled from OpenAI's product releases.
Context
Microsoft 365 Copilot is one of the largest distribution surfaces in enterprise AI, and model placement inside it translates directly into usage volume. The "preferred model" label determines which underlying model handles default Copilot workloads across Word, Excel, Outlook and Teams.
What changed
- GPT-5.6 became Copilot's preferred model on GA day, replacing earlier GPT generations in the default routing position.
- The same week, Bloomberg reported that Microsoft is routing tens of thousands of weekly Excel and Outlook prompts to its internally built MAI models — a server-side change with no visible UI difference.
- Copilot now presents a three-way routing landscape: OpenAI's GPT-5.6 as preferred, Microsoft's MAI models handling selected workloads, and Anthropic's Claude available as an option.
Why it matters
The two moves are not contradictory — they show Microsoft pursuing preferred-partner economics and supplier diversification simultaneously. For OpenAI, day-one preferred status in Copilot extends GPT-5.6's reach into Microsoft's enterprise installed base at zero marginal distribution cost. For Microsoft, the MAI swap reduces per-prompt dependency on both OpenAI and Anthropic, whose models it reportedly paid roughly $500 million per year to use as of January 2026, per Bloomberg's reporting.
Details
The preferred-model designation was part of OpenAI's July 9 launch-day rollout, which also covered ChatGPT, Codex, the API and Figma Make. Microsoft's MAI routing began as a small share of total Copilot volume; Microsoft declined to comment on the Bloomberg report.
Limitations and caveats
Microsoft has not publicly detailed what share of Copilot traffic each model family handles, and neither company has published the commercial terms attached to preferred placement. The MAI routing figures come from a single Bloomberg report, though reprinted by multiple outlets.
Sources
- WindowsForum — GPT-5.6 becomes preferred model for Microsoft 365 Copilot (aggregator, citing OpenAI releases)
- Seattle Times / Bloomberg — Microsoft replaces OpenAI and Anthropic models with its own AI in some apps (reputable press)
*Update note: This post was last reviewed on 2026-07-22. Copilot model-routing shares remain undisclosed.*
Sources
Drafted with AI assistance from source briefs; reviewed for citation completeness and label accuracy.