Agent Framework RC5 released

Today was week 4 of my 6-week seminar training on the Microsoft Agent Framework, and 1 hour before I started, Microsoft released RC5 with breaking changes. The fun of working with technologies that change weekly 🙂

The Microsoft Agent Framework RC5 (Release Candidate 5) introduces several breaking changes aimed at refining the API, improving consistency, and renaming components for clarity. These changes mostly affect how agents are initialized, how tools are handled, and how responses are managed.

Here are the key breaking changes in RC5:

1. Agent and Client Changes:

Responses API Signature Update:

The AsAIAgent() method now requires the model name as a parameter rather than being part of the GetResponsesClient call.

Before:

ChatClientAgent agent = azureOpenAiClient.GetResponsesClient("gpt-5-mini").AsAIAgent();

After:

ChatClientAgent agent = azureOpenAiClient.GetResponsesClient().AsAIAgent(model: "gpt-5-mini");

FoundryAgent Renaming:

Agents within Microsoft Foundry are now specifically designated as FoundryAgent rather than ChatClientAgent.

Removal of Overrides:

Agent Display Name can no longer be overridden, and Agent ID overrides have been removed, ensuring tighter control over agent identity.

2. Tooling and Middleware Changes

Tool Call Approval Renaming:

The class FunctionApprovalRequestContent has been renamed to ToolApprovalRequestContent.

Middleware Renaming:

ToolCallsHandler.ToolCallingMiddleware has been renamed to ToolCallingMiddlewareAsync.

Renamed Data Fields:

RequestJson and ResponseJson are renamed to RequestData and ResponseData to better reflect that not all providers use JSON.

3. API Structure and Model Changes

Model Naming:

DeploymentModelName has been renamed to Model for simplicity.

Default Client Type:

Added DefaultClientType to OpenAI/AzureOpenAI-based providers, allowing users to define if ChatClient or ResponsesAPI is the default for agents that do not explicitly define it.

HandoffBuilder Tightening:

The HandoffBuilder now specifically requires Agent instead of SupportsAgentRun, making the orchestration API stricter.

4. Other Changes

Removed Agent Display Name:

The Agent Display name feature was removed.

Namespace Fixes:

Several fixes were applied to ServiceCollectionExtensions for Google and Anthropic, which might require updating namespaces in existing code.

These updates are designed to lock down the APIs and workflows as the framework moves toward a stable, production-ready release.

Is your company looking for training or consulting on Agent framework and Microsoft Foundry, we stand ready to partner with you to deliver the highest quality in record time for bringing true ROI for your organization. Reach out to us here