(Updated) Microsoft Custom engine agents: Introducing file upload support [MC1179162]

Message ID: MC1179162 (Updated)

Updated December 11, 2025: We have updated the timeline. Thank you for your patience. 

Custom engine agents (CEA) are specialized agentic solutions that can be built using any large language model (LLM), toolchain, or orchestration framework, and are tailored to specific domain or tenant workflows. These agents can be created using either Microsoft Copilot Studio or the Agents Toolkit. File upload support is already available in Microsoft 365 Copilot Business Chat.

We’re now extending this capability to Custom engine agents, enabling users to upload files stored locally or in OneDrive directly to agents. Once uploaded, agents can access the file for a short duration and respond to user queries based on its contents. This update aligns with customer feedback requesting more flexible input options for agent interactions.

[When this will happen:]

General Availability (Worldwide): Rollout will begin in early February 2026 (previously mid-December 2025) and is expected to complete by late February 2026 (previously late December 2025).

[How this affects your organization:]

• Who is affected: All users of Custom engine agents, whether built using Copilot Studio or the Agents Toolkit. This includes users on free, metered, and paid Copilot plans.
• What will happen:
  • Users will be able to upload files directly to Custom engine agents.
  • Supported file types will match those supported by Copilot.
  • Image file support will be added in a future update.
  • The feature will be ON by default once available.
  • No changes to existing admin policies are required.

[What you can do to prepare:]

• Communicate this change to helpdesk staff.
• Update internal documentation if you reference CEA capabilities.
• Review the documentation for details on agent configuration and supported capabilities.

Learn more: Custom engine agents for Microsoft 365 overview | Microsoft Learn

[Compliance considerations:]

Question	Answer	Explanation
Does this change store new customer data, and if so, where is it stored and is the data cached or permanently stored?	Yes	Uploaded files are temporarily accessible to the agent for a few minutes
Does this change introduce or significantly modify AI/ML or agent capabilities that interact with or provide access to customer data?	Yes	Custom engine agents will be able to access uploaded files and respond to user queries based on the file contents.
Does this change provide end users any new way of interacting with generative AI, and if so, how?	Yes	Users can now upload files to agents, expanding interaction beyond text input.

Source: Microsoft

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