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RMCP Roadmap

This roadmap tracks the path to SEP-1730 Tier 1 for the Rust MCP SDK.

Spec 2025-11-25 (suite 0.1.16): Server 100% (30/30) · Client 100% (18/18) Spec 2026-07-28 (suite 0.2.0-alpha.9): Server 92.5% (37/40) · Client 75.0% (24/32)

Target spec: 2026-07-28 (release 2026-07-28)

All 2026-07-28 work carries the 2026-07-28 label and the 2026-07-28 spec milestone. Per-scenario conformance status is tracked in the epic issue: #977 — Tracking: 2026-07-28 spec conformance.

Conformance (baseline 2026-07-13, suite 0.2.0-alpha.9)

  • Server: 3 scenarios (tools-call-with-progress stateless behavior, SEP-2243 server-side custom headers, and server-stateless — the SEP-2575 discovery/negotiation suite at 2/28 checks)
  • Client: 8 scenarios (SEP-2243 headers ×3, request-metadata, and 4 single-check auth failures: SEP-2350 step-up, pre-registration, SEP-2352 AS migration, SEP-2468 issuer validation); fixes for SEP-2350 (#888) and SEP-2352 (#965) are already in review
  • CI: run the full --spec-version 2026-07-28 suites (stateless server) instead of hand-picked scenario lists; re-baseline on each draft-suite bump

Spec features without conformance scenarios

Conformance alone does not cover the full spec surface. Feature work tracked via the milestone:

  • SEP-2567 sessionless MCP via explicit state handles (#870)
  • SEP-2260 server requests must associate with a client request (#873)
  • SEP-2549 follow-up: client-side TTL-honoring cache (#974)

(SEP-2575 discovery & negotiation is covered by the server-stateless conformance scenario; implementation is in review — #869, PRs #973, #943.)

Release

The 2026-07-28 implementation ships as v3.0.0 (release PR #964): MRTR, SEP-2549 cache hints, SEP-2243 standard headers, and the SEP-2106 relaxations are merged but unreleased — tiering and relegation are evaluated against the latest stable release, so cutting v3.0.0 with the remaining conformance fixes is on the critical path. Migration guide (draft, kept current until release): discussion #969.

Tier 1 (non-conformance requirements)

Governance & Policy

  • Create VERSIONING.md — document semver scheme, what constitutes a breaking change, and how breaking changes are communicated
  • Publish a dependency update policy (Tier 1 requires a published policy)
  • Cut v3.0.0 (#964) including all conformance fixes (tier relegation is evaluated against the latest stable release)

Documentation (26/48 → 48/48 features with prose + examples)

Undocumented features (14)

  • Tools — image results
  • Tools — audio results
  • Tools — embedded resources
  • Prompts — embedded resources
  • Prompts — image content
  • Elicitation — URL mode
  • Elicitation — default values
  • Elicitation — complete notification
  • Ping
  • SSE transport — legacy (client)
  • SSE transport — legacy (server)
  • Pagination
  • Protocol version negotiation
  • JSON Schema 2020-12 support (upgrade from partial)

Partially documented features (7)

  • Tools — error handling (add dedicated prose + example)
  • Resources — reading binary (add dedicated example)
  • Elicitation — form mode (add prose docs, not just example README)
  • Elicitation — schema validation (add prose docs)
  • Elicitation — enum values (add prose docs)
  • Capability negotiation (add dedicated prose explaining the builder API)
  • Protocol version negotiation (document version negotiation behavior)

Completed

  • 2025-11-25 server conformance 100% (30 scenarios + pending json-schema-2020-12, server-sse-polling)
  • 2025-11-25 client conformance 100% (18 scenarios + legacy auth/2025-03-26-*)
  • SEP-2322 MRTR (14 server scenarios + sep-2322-client-request-state)
  • SEP-2164 resource not found
  • Cache hints (caching)
  • http-header-validation
  • Issue triage labels (bug, enhancement, needs confirmation, needs repro, ready for work, P0–P3)

Informational (not scored for tiering)

These extension scenarios are tracked but do not count toward tier advancement:

Scenario Tag Status
auth/client-credentials-jwt extension ❌ Failed — JWT aud claim verification error
auth/client-credentials-basic extension ✅ Passed
auth/cross-app-access-complete-flow extension ❌ Failed — sends authorization_code grant instead of jwt-bearer
tasks-* extension Not yet attempted

Fork-specific changes (UserGeneratedLLC fork)

The fork diverges from upstream modelcontextprotocol/rust-sdk on Claude Code CLI support. Baseline posture: skills and code carry only what Claude Code CLI actually honours. See the downstream skill .cursor/skills/create-mcp-primitive/audit-checklist.md for the authoritative Claude-CLI-reality anti-pattern list.

Divergences from upstream

  • Added — anthropic-ext feature: anthropic/maxResultSizeChars, claude/channel + claude/channel/permission capabilities, notify_claude_channel + notify_claude_channel_permission Peer helpers, structured_with_text_fallback helper (Claude Code #41361 workaround), lint::warn_if_over_2kb (Claude Code #43474 2 KB truncation cliff).

Deleted (no Claude-CLI consumer)

  • sep-2243-draft — draft SEP, never implemented in the fork beyond a scaffold; Claude CLI doesn't emit or honour the Mcp-Method / Mcp-Name headers or the x-mcp-header tool-param promotion. Removed 2026-04-23.

Proposed but rejected

  • Peer::notify_tasks_status emitter — the workspace previously substituted via notify_logging_message, but per the Claude-CLI-reality filter both the MCP tasks/* primitive and notifications/message are unrendered / not implemented client-side (anthropics/claude-code#18617, #3174). No consumer; the workspace deleted both paths instead of adding the emitter.
  • search_tools meta-tool helper — Claude CLI already defers MCP tools via its built-in client-side Tool Search. Server-side search_tools would be redundant for the sole consumer.
  • Runtime toolset gating à la github-mcp-server --toolsets — notifications/tools/list_changed is dropped mid-turn on stdio by Claude CLI (anthropics/claude-code#50515). The existing category-level LOAD_INITIALLY = false + load_tool_group pattern is sufficient for HTTP consumers; runtime toolset gating on stdio is a no-op.

Under consideration

  • #[resource] + #[resource_router] + #[resource_handler] macros — would delete ~300 LOC of hand-rolled ResourceRouter<S> boilerplate across the 4 downstream workspace MCPs. Real consumer. Tracked for a future fork PR.
  • Origin header validation — currently listed above under Tier 1 server conformance. allowed_hosts covers Host; Origin needs a first-class allowed_origins field on StreamableHttpServerConfig to match the 2025-11-25 spec requirement.