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SEP-2260 Require Server requests to be associated with a Client request.#2260

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evalstate merged 25 commits into
modelcontextprotocol:mainfrom
evalstate:sep/unsolicitited-req
Mar 10, 2026
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SEP-2260 Require Server requests to be associated with a Client request.#2260
evalstate merged 25 commits into
modelcontextprotocol:mainfrom
evalstate:sep/unsolicitited-req

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@evalstate evalstate commented Feb 16, 2026

Motivation and Context

This PR tightens the scoping of Server to Client requests and to server as notice of upcoming changes where this pattern may not be supported by the underlying transport layer.

How Has This Been Tested?

This PR has been supported by research by @pja-ant on current (public) usage of this pattern.

Breaking Changes

Whilst a specification only change, this stops future use of "unsolicited" server-to-client requests in anticipation of future "stateless" transports.

Types of changes

  • Bug fix (non-breaking change which fixes an issue)
  • New feature (non-breaking change which adds functionality)
  • Breaking change (fix or feature that would cause existing functionality to change)
  • Documentation update

Checklist

  • I have read the MCP Documentation
  • My code follows the repository's style guidelines
  • New and existing tests pass locally
  • I have added appropriate error handling
  • I have added or updated documentation as needed

Additional context

This PR has previously been reviewed by the Transports Working Group here: modelcontextprotocol/transports-wg#8

@evalstate evalstate changed the title SEP-xxxx Require Server requests to be associated with a Client request. SEP-2260 Require Server requests to be associated with a Client request. Feb 16, 2026
@PederHP
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PederHP commented Feb 16, 2026 •
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Maybe explicitly exclude or include pings as valid requests to associate with? They have a request id, but I suppose they're not that useful for stateless transports. It would also be a kind of workaround to not having unsolicited server-initiated requests.

@chemicL chemicL mentioned this pull request Feb 17, 2026
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Comment thread seps/2260-Require-Server-requests-to-be-associated-with-Client-requests.md
@evalstate evalstate requested a review from a team as a code owner February 17, 2026 23:59
evalstate and others added 9 commits February 18, 2026 00:18
@evalstate
Open SEP from transports-wg original discussion here: modelcontextpro…
755745c 
…tocol/transports-wg#8
@evalstate
update title
398dbc3
@evalstate @CaitieM20
Update seps/0000-Require-Server-requests-to-be-associated-with-Client…
1c77e5a 
…-requests

Co-authored-by: Caitie McCaffrey <caitiem20@github.com>
@evalstate @CaitieM20
Update seps/0000-Require-Server-requests-to-be-associated-with-Client…
808f545 
…-requests

Co-authored-by: Caitie McCaffrey <caitiem20@github.com>
@evalstate
Use .md extension
551acc6
@evalstate
Rename to include PR# in name
709e7b8
@evalstate
Fix markdown formatting issues in SEP-2260
54cd446 
- Fixed missing closing backtick in Abstract (sampling/createMessage, elicitation/create)
- Fixed typo: 'Reqeusts' -> 'Requests' in Design Intent section
@evalstate
Fix markdown formatting and generate SEP documentation
4d23496 
- Fixed Prettier formatting in SEP-2260 markdown file
- Generated SEP documentation and updated docs index
- Fixed missing closing backtick and typo in Abstract and Design Intent sections
@evalstate
Fix broken anchor links in documentation
a226dc4 
- Remove trailing slash from ping#implementation-considerations link
- Fix anchor reference for getting-logs-from-claude-desktop section
@evalstate evalstate force-pushed the sep/unsolicitited-req branch from db2a164 to a226dc4 Compare February 18, 2026 00:19
pcarleton
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evalstate commented Feb 18, 2026

I've made the wording consistent, and excluded Ping from the requirement.

@CaitieM20 CaitieM20 added accepted SEP accepted by core maintainers, but still requires final wording and reference implementation. and removed draft SEP proposal with a sponsor. labels Feb 25, 2026
evalstate
evalstate commented Feb 27, 2026
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Would clients need to ensure the invariant holds true that requests cannot be? What is the recommended error handling here?

Error handling guidance added

@evalstate evalstate enabled auto-merge February 27, 2026 18:48
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@evalstate evalstate requested a review from a team as a code owner March 10, 2026 21:02
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LGTM

@evalstate evalstate merged commit e148315 into modelcontextprotocol:main Mar 10, 2026
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@markdroth markdroth mentioned this pull request Mar 12, 2026
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@mcp-virtual-tpm mcp-virtual-tpm Bot added this to the 2026-06-30-RC milestone Apr 17, 2026
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@mikekistler mikekistler mentioned this pull request Apr 30, 2026
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@CaitieM20 CaitieM20 mentioned this pull request May 15, 2026
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@CaitieM20 CaitieM20 added final SEP finalized. and removed accepted SEP accepted by core maintainers, but still requires final wording and reference implementation. labels May 15, 2026
@mikekistler mikekistler mentioned this pull request May 19, 2026
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qdrddr commented May 25, 2026 •
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Can I pull a user query from the client prior to the LLM call with this SEP?

My problem I want to fix:
Current MCP SPEC has a major limitation:

  1. It is not designed to integrate cleanly with harness/runtime hooks such as those used by Anthropic Claude Code/ OpenAI Codex etc.
  2. It is not agent session-aware. MCP servers are initialized before agent sessions start, so notifications/tools/list_changed operates effectively at the agent/process level rather than per agent session or subagent.
  3. I can't get the user query prior to the LLM call to adjust the MCP tools listed for the LLM.

As a result, when multiple sessions or subagents require different tool sets, there is no reliable way to target notifications/tools/list_changed to a specific agent session. The same agent instance may therefore expose inconsistent tools across concurrent contexts.

This makes dynamic tool manipulation difficult in real-world agent environments.

This was referenced May 26, 2026
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Labels

final SEP finalized. SEP transport Related to MCP transports

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2026-07-28-RC

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@evalstate @PederHP @qdrddr @pcarleton @CaitieM20 @markdroth @dsp-ant @localden