Table of Contents
Summary
- Microsoft 365 Copilot declarative agents will upgrade to the GPT-5.1 model with an automatic selection of the best model based on user prompts.
- Advanced reasoning model will be available for complex queries.
- No admin configuration changes are needed; the feature will be enabled by default for applicable tenants.
- All tenants using Microsoft 365 Copilot declarative agents are affected by this change.
- The change is categorized as a new feature with both user and admin impacts.
Admin Impact: Low
User Impact: Low
Release Start: 15 Dec 2025
Release End: 15 Jan 2026
Services: M365 Copilot
Category: Stay informed
Tags: New Feature, User Adoption, Admin Action
History
12/10/2025 Item Added to Message Center
Microsoft Message
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.