SDK tiers
SDK tiers - The three-tier classification for MCP SDKs: Tier 1 requires 100% conformance-test pass rate and same-release protocol support, Tier 2 requires 80% conformance and six-month feature timelines, Tier 3 is experimental. Advancement runs through self-assessment, conformance testing, and SDK Working Group approval.
The SDK tier system is the protocol's maintenance contract with its implementations. Tier 1 SDKs pass 100% of the automated conformance tests, ship new protocol features before a spec release on an agreed timeline, triage issues within two business days, and fix critical bugs within seven days. Tier 2 requires 80% conformance and six-month feature timelines; Tier 3 carries no commitments. Extensions such as Tasks and MCP Apps are not required for any tier.
Movement is mechanical in both directions: maintainers request advancement through self-assessment, conformance runs, and SDK Working Group approval, and an SDK that fails conformance continuously for four weeks is relegated. Tier changes are recurring news events; the Ruby SDK's promotion to Tier 2 alongside its 1.0.0 release is the catalog's first covered example.
Sources and verification
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