# MCP Tasks Extension: Polling for Long-Running Tool Calls (SEP-2663) > What the MCP Tasks extension is: the official io.modelcontextprotocol/tasks mechanism that lets a server return a pollable task handle instead of blocking on a slow tools/call — tasks/get, tasks/update, tasks/cancel, the five task states, and how it differs from the removed 2025-11-25 experimental tasks feature. Category: Reference · Updated: 2026-08-11 · Tags: mcp, protocols, spec, tasks, async, long-running-operations, agents, standard Canonical: https://changegamer.ai/resources/mcp-tasks-extension Variants: [HTML](https://changegamer.ai/resources/mcp-tasks-extension) · [JSON](https://changegamer.ai/api/resources/mcp-tasks-extension.json) License: https://changegamer.ai/license.xml · Access: free A `tools/call` that takes 30 seconds — a batch job, a deep-research query, a video render — has no good home in a request/response protocol: block the connection and risk a timeout, or design a bespoke polling scheme per server. The **Tasks extension** is MCP's official answer: a server can respond to `tools/call` with a durable task handle instead of a final result, and the client polls a standard method until it is done. ## Key facts - Tasks is **SEP-2663** (`io.modelcontextprotocol/tasks`), status **Final**, authored by Luca Chang and Caitie McCaffrey for the MCP Agents Working Group. It shipped as one of the first official extensions alongside the 2026-07-28 spec revision (see /resources/mcp-2026-spec-revision), with AWS named as a first contributor. - It **replaces**, not extends, the experimental core "tasks" feature from the prior 2025-11-25 spec. The two are explicitly **not wire-compatible**: the old `tasks/result` and `tasks/list` methods, and the old per-request opt-in capability flag, are gone. Code or docs describing the 2025-11-25 tasks shape no longer apply. - Three new methods: **`tasks/get`** (idempotent poll, returns full task state including any pending input requests), **`tasks/update`** (client submits a response to a pending input request), and **`tasks/cancel`** (client signals cancellation intent; eventual-consistency, not a guaranteed hard stop). - Task creation still requires client opt-in: a client must declare the `io.modelcontextprotocol/tasks` extension capability on its request before a server may return a task. Per SEP-2663, a server **MUST NOT** return `CreateTaskResult` to a client that did not include the extension capability on its request — the opt-in is now a single per-request capability declaration rather than the old two-part handshake, not a removal of client opt-in. When a server does return a task, the `tools/call` result carries a new `resultType: "task"` discriminator instead of the normal result shape. - Five task statuses: **`working`** (processing), **`input_required`** (server is waiting on a client `tasks/update` response), **`completed`** (final result available via `tasks/get`), **`failed`** (a JSON-RPC error occurred), **`cancelled`**. - It was designed to fit the same spec revision's other changes: no unsolicited server-to-client streams (SEP-2260), no protocol-level session to scope a task to (SEP-2567/SEP-2575 statelessness), and routing via the `Mcp-Name` header (SEP-2243). ## What an agent/client builder should do 1. Declare the `io.modelcontextprotocol/tasks` extension capability on your request before calling a tool you expect might run long — a server will reject task creation and refuse to return `CreateTaskResult` if this capability was not included on the request. 2. Don't assume a `tools/call` blocks until done — check the response for `resultType: "task"` before treating the payload as a final result. 3. If a task comes back, poll `tasks/get` (not a held-open stream) until status leaves `working`; if status is `input_required`, answer via `tasks/update` before polling again. 4. Treat `tasks/cancel` as best-effort — a subsequent `tasks/get` may still show the task completing or failing rather than immediately reporting `cancelled`. 5. If you maintain an MCP server or client built against the 2025-11-25 spec's experimental tasks feature, this is a breaking rewrite, not a version bump — the method names and capability model both changed. ## Distinct from adjacent ChangeGamer resources - **Not durable execution** (/resources/durable-execution-for-agents): that resource covers checkpointing an *agent's own* orchestration logic (e.g. Temporal-style workflow engines) across restarts. The Tasks extension is a narrower, wire-level mechanism for one MCP server call to hand back a pollable handle — an agent can use durable-execution tooling on top of a Tasks-based tool call, but the two solve different problems. - **Not streaming** (/resources/streaming-for-agents): that resource covers token/event streams (SSE, chunked responses) for incremental output. Tasks is poll-based by design — no held-open connection — specifically because SEP-2260 forbids unsolicited server-to-client pushes in the stateless 2026-07-28 architecture. - **Not MCP Apps** (/resources/mcp-apps-explained): a different extension from the same spec revision, for server-rendered interactive UI, unrelated to async task polling. ## Verified sources Primary (fetched directly this session): - SEP-2663 source (SEP number, status, authors, methods, discriminator, task statuses, client capability opt-in requirement, relationship to the removed 2025-11-25 feature): https://raw.githubusercontent.com/modelcontextprotocol/modelcontextprotocol/main/seps/2663-tasks-extension.md - MCP blog, "The 2026-07-28 Specification" (Tasks as a first official extension, AWS as contributor): https://blog.modelcontextprotocol.io/posts/2026-07-28/ Secondary — WebSearch-only, not independently re-fetched this session (modelcontextprotocol.io returned EGRESS_BLOCKED to direct WebFetch): - Extension overview page (surfaced via search, matches the SEP file's own description of the poll loop): https://modelcontextprotocol.io/extensions/tasks/overview See also: /resources/mcp-2026-spec-revision, /resources/mcp-primitives, /resources/mcp-apps-explained, /resources/durable-execution-for-agents, /resources/streaming-for-agents. --- ## Related resources - [MCP Goes Stateless: The 2026-07-28 Spec Revision Explained](https://changegamer.ai/resources/mcp-2026-spec-revision.md): What changes in MCP's largest revision since launch: SEP-2575/SEP-2567 remove the session handshake and Mcp-Session-Id header for explicit state handles, new Mcp-Method/Mcp-Name routing headers, full JSON Schema 2020-12 tool schemas, and six authorization-hardening SEPs — shipped as final, on schedule, on 2026-07-28. - [MCP Apps Explained: The Official Interactive-UI Extension for MCP](https://changegamer.ai/resources/mcp-apps-explained.md): What MCP Apps (SEP-1865) is: the ui:// resource scheme and sandboxed-iframe/JSON-RPC bridge it defines for MCP tools to return rendered UI instead of plain text, how it relates to the community MCP-UI project and OpenAI's Apps SDK, and which hosts support it. - [NLWeb Explained: Microsoft's Natural-Language Query Protocol for Websites](https://changegamer.ai/resources/nlweb-explained.md): What NLWeb is: the open, MIT-licensed protocol that lets a site answer natural-language questions over its own Schema.org data via /ask and /mcp endpoints, who built it, and how it differs from llms.txt, AGENTS.md, and a generic MCP server. - [WebMCP: Browser-Native Tool Registration for In-Page AI Agents](https://changegamer.ai/resources/webmcp.md): What WebMCP is: the W3C Web Machine Learning Community Group browser API letting a page register its own tools (via document.modelContext or plain HTML forms) for an in-browser agent to call directly, the live Chrome and Edge origin trials, and how it differs from MCP itself. --- ## Further reading - [How to Implement OAuth 2.1 for an MCP Server](https://changegamer.ai/articles/mcp-oauth-implementation.md): A wire-level implementation walkthrough for OAuth 2.1 on a remote MCP server: what the discovery documents actually contain, CIMD vs. Dynamic Client Registration in your server code, per-SEP detail from the 2026-07-28 hardening set, and token-validation mechanics. - [MCP Authentication and the Production MCP Server Playbook](https://changegamer.ai/articles/mcp-server-in-production.md): MCP authentication with OAuth 2.1, plus transport, tool design, versioning, testing, distribution and observability for a production MCP server. --- Index of all resources: https://changegamer.ai/llms.txt · Full corpus: https://changegamer.ai/llms-full.txt · Corpus data (NDJSON): https://changegamer.ai/api/corpus.jsonl · Offers: https://changegamer.ai/api/pricing.json License the full corpus for RAG / fine-tuning (AI-use grant): https://changegamer.ai/corpus-license