MCP tasks/get -32601: debug the 2026-07-28 Tasks extension

The key distinction

MCP 2026-07-28 support does not equal MCP Tasks support

Fast diagnosis

What each symptom usually means

Era mismatch

The 2025 experimental API and 2026 extension are not wire-compatible

A particularly useful clue is tasks/result: SEP-2663 explicitly removes it, so -32601 is the correct modern response. The final result is embedded in the terminal tasks/get response. tasks/list is also removed; persist the returned taskId instead of depending on global enumeration.

Known-good request shape

Poll with extension capability plus task routing metadata

Over Streamable HTTP, a modern task poll needs the normal 2026 request metadata plus transport headers. The critical routing rule is that Mcp-Name equals the task ID for tasks/get, tasks/update and tasks/cancel.

POST /mcp
MCP-Protocol-Version: 2026-07-28
Mcp-Method: tasks/get
Mcp-Name: task_7f31
Content-Type: application/json

{
  "jsonrpc": "2.0",
  "id": 9,
  "method": "tasks/get",
  "params": {
    "taskId": "task_7f31",
    "_meta": {
      "io.modelcontextprotocol/protocolVersion": "2026-07-28",
      "io.modelcontextprotocol/clientCapabilities": {
        "extensions": {
          "io.modelcontextprotocol/tasks": {}
        }
      }
    }
  }
}

If this shape is correct and you still get -32601, inspect the SDK/framework support matrix before changing your task store. A transport or dispatcher can reject the method before your registered handler ever runs.

Current implementation reality

Schemas can exist before end-to-end Tasks support does

Repair sequence

Eight checks before writing a workaround

1. 1. Capture the protocol revision. Prove the request is actually using 2026-07-28 rather than assuming from an SDK version.
2. 2. Verify extension negotiation. Confirm the client declares io.modelcontextprotocol/tasks and the server advertises/accepts it on the relevant flow.
3. 3. Inspect the original tool result. A task-aware client must be able to accept resultType: "task" instead of only an ordinary CallToolResult.
4. 4. Remove legacy methods. Replace tasks/result with terminal tasks/get; do not rely on tasks/list.
5. 5. Send routing headers. Set Mcp-Method and Mcp-Name: <taskId> on Streamable HTTP task requests.
6. 6. Honor pollIntervalMs. Poll at the server-directed interval and accept that it can change while the task is working.
7. 7. Check framework dispatch. If the request is correct but never reaches your handler, confirm whether the framework has an open Tasks-extension gap for that path.
8. 8. Keep task state durable and authorized. Bind every task to its owner/authorization context, set expiry and quotas, and do not depend on one process or transport session surviving.

Why Mcp-Name matters

Stateless protocol does not mean stateless application work

A task can outlive the HTTP connection and even the server process that created it. The protocol therefore routes subsequent task operations using an explicit task handle. Put durable task state behind that handle, authorize every status/update/cancel call, and make infrastructure capable of routing or resolving the task without an implicit MCP session. Mcp-Name helps infrastructure route the request; it is not an authorization decision by itself.

Sources

Protocol and implementation evidence checked 13 September 2026

• SEP-2663: Tasks Extension — canonical lifecycle, negotiation, tasks/get/tasks/update/tasks/cancel, retired legacy methods and required task routing header behavior.
• TypeScript SDK issue #2598 — current report of extension handlers for tasks/get/tasks/cancel being shadowed and rejected with -32601 on a v2 path.
• Python SDK roadmap — current implementation-status note that the 2026 Tasks extension remains outside the implemented v2 extension set.
• Cloudflare Agents issue #2135 — current request for Tasks support on the stateless createMcpHandler path.
• Agentic AI Foundation Tasks walkthrough — concrete modern tasks/get, Mcp-Name and pollIntervalMs examples.

Continue the implementation path