{"name":"MCP_SDK_GENERATION","slug":"mcp-sdk-generation","family":"env","title":"Environment variables","noun":"environment variable","description":"MCP SDK generation gate tengu_brindle_causeway now defaults to on, favoring MCP SDK generation v2 when not set explicitly","description_source":"entry","described_by":{"version":"2.1.274","anchor":"mcp-sdk-generation-default-flips-to-v2-via-tengu-brindle-cau"},"presence":{"first_seen":"2.1.218","removed_in":null,"in_current_build":true,"newest_mined":"2.1.308","builds":79,"mined_builds":149,"first_cited":{"version":"2.1.218","released_at":"2026-07-22 19:55:32","spans":1}},"aliases":[],"entries":[{"version":"2.1.274","anchor":"mcp-sdk-generation-default-flips-to-v2-via-tengu-brindle-cau","heading":"MCP SDK generation default flips to v2 via tengu_brindle_causeway","line":"MCP SDK generation gate tengu_brindle_causeway now defaults to on, favoring MCP SDK generation v2 when not set explicitly","released_at":"2026-09-16 22:36:09","reason":"found in this entry's text"},{"version":"2.1.274","anchor":"mcp-client-sdk-runtime-now-defaults-to-v2-not-v1","heading":"MCP client SDK runtime now defaults to v2, not v1","line":"MCP client runtime's compiled fallback flipped from v1 to v2","released_at":"2026-09-16 22:36:09","reason":"named in this entry, found in this entry's text"},{"version":"2.1.218","anchor":"mcp-sdk-v2-feature-flagged","heading":"MCP SDK v2 [Feature-Flagged]","line":null,"released_at":"2026-07-22 19:55:32","reason":"found in this entry's text"},{"version":"2.1.218","anchor":"mcp-sdk-version-selection","heading":"MCP SDK Version Selection","line":null,"released_at":"2026-07-22 19:55:32","reason":"found in this entry's text"}],"entries_total":4,"docs":[{"source":"claude-code","path":"errors","title":"Error reference","documented":false},{"source":"claude-code","path":"mcp","title":"Connect Claude Code to tools via MCP","documented":false}],"docs_total":2,"gates":[],"related":[{"name":"MCP_CLIENT_SECRET","slug":"mcp-client-secret","description":"OAuth client secret for an MCP server, used instead of prompting. When the client secret is requested and `MCP_CLIENT_SECRET` is non-empty, its value is used; otherwise Claude Code prompts `Enter OAuth client secret: ` on stderr, and with no TTY it fails with `No TTY available to prompt for client secret. Set MCP_CLIENT_SECRET env var instead.`"},{"name":"MCP_CONNECT_TIMEOUT_MS","slug":"mcp-connect-timeout-ms","description":"Very large MCP_TIMEOUT values are capped instead of overflowing and timing out instantly."},{"name":"MCP_CONNECTION_NONBLOCKING","slug":"mcp-connection-nonblocking","description":"Five more environment variables, including stream and byte watchdogs, can be set in settings.json."},{"name":"MCP_DISCOVERY_CACHE","slug":"mcp-discovery-cache","description":"Startup no longer dials cached HTTP or SSE MCP servers; they restore from cache and connect on first use."},{"name":"MCP_DISCOVERY_CACHE_MAX_STALE_S","slug":"mcp-discovery-cache-max-stale-s","description":"Cached MCP server discovery is dropped after repeated connection failures instead of only on age."},{"name":"MCP_DISCOVERY_CACHE_STRIKES","slug":"mcp-discovery-cache-strikes","description":"Cached MCP server discovery is dropped after repeated connection failures instead of only on age."},{"name":"MCP_DISCOVERY_CACHE_TTL_S","slug":"mcp-discovery-cache-ttl-s","description":"Cached MCP server discovery is dropped after repeated connection failures instead of only on age."},{"name":"MCP_OAUTH_CALLBACK_PORT","slug":"mcp-oauth-callback-port","description":"About 220 environment variables now parse and validate in one place, including bounds checks."},{"name":"MCP_OAUTH_CLIENT_METADATA_URL","slug":"mcp-oauth-client-metadata-url","description":"MCP OAuth stops sending a client id that only works for loopback, and repairs saved entries."},{"name":"MCP_PROTOCOL_NEGOTIATION","slug":"mcp-protocol-negotiation","description":"A newer MCP protocol handshake exists per transport but every gate falls back to legacy here."}],"url":"https:\/\/changelogs.core-directive.com\/reference\/env\/mcp-sdk-generation","family_url":"https:\/\/changelogs.core-directive.com\/reference\/env.json"}