[2026-07-28] Extensions framework + Tasks + MCP Apps #335

Tracking issue for the MCP Spec 2026-07-28 release — Extensions framework + Tasks + MCP Apps milestone.

SEP-2133 establishes the extension mechanism (capability negotiation + extensible handler dispatch). Both SEP-2663 (Tasks) and SEP-1865 (MCP Apps) graduate to extensions on top of it. Land SEP-2133 first; Tasks and Apps depend on it.

SEPs covered

Sub-issues

Foundation (blocker for Tasks and Apps):

• [Schema][Server][Client] SEP-2133: Extensions framework (capability negotiation + ExtensionRegistry + extensible dispatch) #344 — SEP-2133: Extensions framework (capability negotiation + ExtensionRegistry + extensible dispatch)

SEP-2663 Tasks:

• [Schema] SEP-2663 Tasks: Task shape, resultType discriminator, tasks/* request/result types #345 — Schema: Task shape, resultType discriminator, tasks/* request/result types
• [Server] SEP-2663 Tasks: TasksExtension, capability gate, tasks/* handlers #346 — Server: TasksExtension, capability gate, tasks/get/update/cancel handlers
• [Server] SEP-2663 Tasks: TaskStoreInterface with InMemory and PSR-16 stores #347 — Server: TaskStoreInterface with InMemory and PSR-16 stores
• [Server] SEP-2663 Tasks: Handlers return task handles; the application advances the task #348 — Server: Handlers return task handles; the application advances the task
• [Client] SEP-2663 Tasks: Poll task handles and answer inputRequests #349 — Client: Poll task handles and answer inputRequests via tasks/update

SEP-1865 MCP Apps:

• [Schema] SEP-1865 MCP Apps: Content types, ui:// scheme, tool metadata fields #350 — Schema: Content types, ui:// scheme, tool metadata fields
• [Server][Capability] SEP-1865 MCP Apps: ext-apps registration, builder API, #[McpUiResource] attribute #351 — Server: ext-apps registration, builder API, #[McpUiResource] attribute
• [Server][Capability][Examples] SEP-1865 MCP Apps: Link tools to UI templates via attribute metadata + example/inspector tests #352 — Server/Examples: Link tools to UI templates + example server + inspector tests

Notes

• All three SEPs are merged into the spec repo.
• SEP-2663 supersedes SEP-1686. Issue [Schema][Server][SEP-1686] Tasks #139 (SEP-1686 Tasks) was closed and rescoped to this milestone — the SEP-1686 design was never shipped by the PHP SDK, so there is nothing to deprecate.
• SEP-1865 spec lives at modelcontextprotocol/ext-apps.