GPT-5.6 becomes 'preferred model' in Microsoft 365 Copilot — even as Microsoft routes some prompts to its own MAI models

Microsoft announced immediate availability of GPT-5.6 inside Microsoft 365 Copilot, optimized for knowledge work: turning rough ideas into polished drafts, clearer analyses, and multi-step tasks across the Office suite. OpenAI framed it as deepening the partnership, calling 5.6 the 'preferred model' for Copilot 365.

The subtext is more interesting than the headline. Bloomberg reported Microsoft has begun rerouting tens of thousands of weekly Excel and Outlook prompts to its own MAI models to reduce reliance on premium OpenAI and Anthropic tokens — a move a 248-upvote r/OpenAI thread seized on as evidence the alliance is fraying. The two facts sit in tension: publicly Microsoft elevates GPT-5.6, operationally it is diversifying to protect margins.

This mirrors the week's broader cost-pressure theme. OpenRouter data shows Chinese open-source models running 60–90% cheaper, and Vercel's CEO argued single-lab loyalty is obsolete — 'every piece is plug and play.' Microsoft rerouting its own flagship Copilot prompts to cheaper house models is the enterprise version of that same multi-model hedging, and worth watching as a leading indicator of how the OpenAI–Microsoft relationship evolves.