René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Backwards compatibility \u0026 version negotiation","articleBody":"Tracks: #2803\n\nMake 2026-07-28 a real version the SDK can speak alongside every prior one: per-instance version knobs, the era classifier, and per-request `_meta` validation on the server. This is where the stateless server-side obligations land.\n\n## What's in it\n\n- Per-instance \"what versions do I serve/speak\" knobs (server + client); add 2026-07-28 to the negotiable set.\n- Era classifier + dispatch: server reads the `_meta` envelope (version/clientInfo/capabilities), validates it, emits the unsupported-version / missing-capability errors with typed data, and skips the legacy init gate for modern traffic.\n- Era-gate everything removed from core for modern peers: `ping`, `logging/setLevel`, `roots/list_changed`, the tasks surface, the URL-elicitation-required error.\n- `resultType` stamped on every modern result (the strip-for-legacy half is already in #2849).\n\n## Conformance\n\n- (no scenario passes on this alone — it's the foundation the others stand on)\n- Together with _New HTTP serving path (modern + dual-era)_, _Capabilities API + server/discover handler_, _subscriptions/listen_, _Context object (layered, per-request)_: `server-stateless`\n- Together with #2894: `request-metadata`\n\n## Dependencies\n\n- Depends on: none\n\n## References\n\n- [Versioning](https://modelcontextprotocol.io/specification/draft/basic/versioning)\n- [SEP-2575](https://github.com/modelcontextprotocol/modelcontextprotocol/pull/2575)\n- [SEP-2567](https://github.com/modelcontextprotocol/modelcontextprotocol/pull/2567)\n- [sep-2575.yaml](https://github.com/modelcontextprotocol/conformance/blob/main/src/seps/sep-2575.yaml)\n","author":{"url":"https://github.com/maxisbey","@type":"Person","name":"maxisbey"},"datePublished":"2026-06-17T11:11:50.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":1},"url":"https://github.com/2892/python-sdk/issues/2892"}