{"version":"2.1.259","anchor":"mcp-client-capabilities-header-gains-a-discover-protocol-ver","canonical_anchor":"mcp-client-capabilities-header-gains-a-discover-protocol-ver","heading":"MCP client-capabilities header gains a discover-protocol-version companion header","tier":"internal","area":"MCP","scope":null,"heads_up":null,"url":"https:\/\/changelogs.core-directive.com\/v\/2.1.259\/e\/mcp-client-capabilities-header-gains-a-discover-protocol-ver","release_url":"https:\/\/changelogs.core-directive.com\/v\/2.1.259","markdown":"### MCP client-capabilities header gains a discover-protocol-version companion header\n\nclaude.ai MCP calls now send a discover-protocol-version header whenever the discovery mode isn't off.\n\nOutgoing headers for claude.ai MCP calls now also include an `anthropic-mcp-discover-protocol-version` header, added when the mode value is not `\"off\"`. The existing client-capabilities header is now skipped only when both a renamed check and `mode === \"off\"` fail, whereas previously it was skipped whenever a single check failed.\n\n- Area: MCP\n- Tier: Under the hood\n- Useful: 2\/5\n- Signal: 3\/5"}