.NET: [Feature]: Support MCP 2026-07-28 specification (including Tasks Extension) in Agent Framework .NET MCP Connector

[Pratik-Shah]

Description

We are using Microsoft Agent Framework (.NET/C#) with Foundry-hosted agents and are migrating our tools to become MCP-native. As part of this effort, we attempted to connect Agent Framework to MCP servers implementing the latest MCP specification (2026-07-28), including long-running operations exposed through the Tasks Extension.

During testing we observed that the native Agent Framework MCP integration does not behave as an MCP 2026-07-28 client.

Specifically, the connector does not negotiate or advertise the MCP 2026 Tasks Extension capability during initialization.

Expected MCP 2026 initialization:
{
"protocolVersion": "2026-07-28",
"capabilities": {
"tools": {},
"extensions": {
"io.modelcontextprotocol/tasks": {}
}
}
}

Instead, Agent Framework appears to operate using MCP 2025-11-25 semantics and does not expose the required capability.

The visible symptom was: missing / unsupported io.modelcontextprotocol/tasks capability

As a result, MCP servers implementing the MCP 2026-07-28 specification cannot be consumed through the native Agent Framework MCP connector.

This is not limited to task execution alone. The observation suggests the connector currently targets MCP 2025-11-25 rather than the newer MCP 2026-07-28 protocol surface.

What worked

We successfully got long-running operations working through the Agent Framework MCP connector by exposing a compatibility endpoint that follows the older MCP task model.

Our MCP server exposes:
protocolVersion = 2025-11-25
execution.taskSupport = required

Workflow:
tools/call
↓
returns task handle

tasks/get
↓
poll status

tasks/result
↓
retrieve final result

Agent Framework works successfully with this approach.

What did not work
When using an MCP server implementing MCP 2026-07-28:
-Protocol negotiation to 2026-07-28
-Tasks Extension advertisement
-MCP 2026 task lifecycle
-MCP 2026 request/response schemas were not supported through the native Agent Framework MCP connector.

In contrast, using the newer MCP SDK path directly worked with the MCP 2026 protocol and Tasks Extension.

Comparison

1. Agent Framework Native MCP Connector --> Works with MCP 2025-11-25 compatibility model
2. Direct MCP SDK Integration --> Works with MCP 2026-07-28

This suggests that the gap exists in Agent Framework's MCP connector layer rather than in the underlying MCP ecosystem.

Solution needed:
Add first-class support for MCP 2026-07-28 in the Agent Framework .NET MCP connector.

This includes:

• Protocol support
• Support negotiation to 2026-07-28
• MCP 2026 request/response schemas
• MCP 2026 capability negotiation
• Extensions support
  Support MCP extensions introduced in the MCP 2026 model, including:
  {
  "extensions": {
  "io.modelcontextprotocol/tasks": {}
  }
  }

Task support: Support the MCP 2026 task lifecycle:
tools/call
tasks/get
tasks/result
tasks/cancel

Backward compatibility: Continue supporting existing flows to avoid breaking current applications.:
protocolVersion = 2025-11-25
execution.taskSupport = required

Code Sample

Language/SDK

Both