Microsoft 365 Copilot: Declarative agents model upgrade to GPT-5.1

Microsoft 365 Copilot declarative agents will upgrade to the GPT-5.1 model with an auto architecture by mid-January 2026. The upgrade enables advanced reasoning for complex queries, requires no admin changes, is enabled by default, and affects all tenants using these agents. No action or compliance concerns are noted. Introduction Microsoft 365 Copilot declarative agents are upgrading to the GPT-5.1 model, which uses an “auto” architecture. The orchestrator will automatically select the best model for each scenario, either the fast “chat” model or the advanced reasoning model, based on the user prompt. When this will happen General Availability (Worldwide): Rollout will begin mid-December 2025 and is expected to complete by mid-January 2026. How this affects your organization Who is affected: All tenants using Microsoft 365 Copilot declarative agents. What will happen: Declarative agents will upgrade to GPT-5.1. The advanced reasoning model will be available for complex queries. No admin configuration changes are required. Feature will be enabled by default for all applicable tenants. What you can do to prepare No action is required. Compliance considerations No compliance considerations identified. Review as appropriate for your organization. Message ID: MC1194070

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