Stateless MCP removes initialize and sessions; to migrate safely, capture a legacy baseline, migrate one layer at a time, run a two-era test matrix, normalize diffs, and validate agent behavior.
Capture a full legacy baseline (tools/list, golden tools/call, error envelopes) with MCP Inspector pinned to the legacy era before any dependency upgrades.
Run every scenario against the migrated server in both eras (legacy and 2026-07-28) and confirm which era each connection negotiated.
Create named tests for features removed in 2026-07-28 (initialize, sessions, ping/logging/setLevel) and verify the server rejects or ignores legacy-only inputs.
# What changed and why it matters Stateless MCP (2026-07-28 revision) drops the initialize handshake and sessions. Every request now carries protocol version and client capabilities in _meta. Servers must implement server/discover to advertise supported versions, capabilities, and identity. Code or tests that relied on per-session headers or an initialize exchange will break or behave differently.
# Migration approach at a glance Treat this like any regression job: freeze the legacy output, change one layer at a time, and finish by testing the agents that call your server. The migration checklist below walks through concrete checks you can run with MCP Inspector and your existing test harness.
# Five concrete regression checks
# Practical test order and tips
# Conclusion
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