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

Product:

Copilot, Microsoft 365 Copilot, OneDrive

Platform:

Online, World tenant

Status:

Change type:

Admin impact, New feature, Updated message, User impact

Links:

Details:

Summary:
Microsoft is adding file upload support to Custom engine agents, allowing users to upload files from local storage or OneDrive for agent interaction. This feature, already in Microsoft 365 Copilot Business Chat, will roll out globally from February 2026, be enabled by default, and require no admin changes.

Details:
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).

Change Category:
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Scope:
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Release Phase:

Created:
2025-10-25

updated:
2025-12-12

Task Type

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Docu to Check

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MS How does it affect me

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MS Preperations

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summary for non-techies**

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Direct effects for Operations**

File Upload Support
Users may experience confusion or frustration if they are not aware of the new file upload feature, leading to potential misuse or security concerns regarding file types and content.
   - roles: End Users, Helpdesk Staff
   - references: https://learn.microsoft.com/microsoft-365-copilot/extensibility/overview-custom-engine-agent

Data Access and Security
The introduction of file uploads may lead to security vulnerabilities if users upload sensitive information without proper guidelines, potentially exposing the organization to data breaches.
   - roles: IT Security Team, Compliance Officers
   - references: https://learn.microsoft.com/microsoft-365-copilot/extensibility/overview-custom-engine-agent

Configutation Options**

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Data Protection**

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explanation for non-techies**

Microsoft is introducing a new feature that allows users to upload files to Custom engine agents, which are specialized tools designed to help with specific tasks. Think of these agents like a personal assistant who can help you with tasks by using information you provide. Previously, you could only interact with these agents through text, like having a conversation. Now, you can also share files with them, similar to handing a document to your assistant to get their input.

This feature is similar to when you use a smartphone app that lets you upload photos or documents directly from your phone or cloud storage. In this case, you can upload files from your computer or OneDrive to the agent. Once the file is uploaded, the agent can look at it for a short time and use the information to help answer your questions or complete tasks. This is like giving your assistant a file to review and then having them give it back after they’ve used it to help you.

The rollout of this feature will start in February 2026 and will be available to all users of Custom engine agents, regardless of their subscription plan. The feature will be turned on automatically, so you won't need to change any settings or ask your IT department to make adjustments. However, it’s a good idea to let your helpdesk staff know about this update and update any internal documents that describe how to use these agents.

From a compliance perspective, it's important to note that the files you upload are only temporarily accessible to the agent, much like how a document might be temporarily reviewed by someone and then returned to you. This ensures that your data is not stored permanently by the agent. The ability to upload files expands how you can interact with these agents, making them more versatile and useful for a variety of tasks.