{"version":"2.1.323","anchor":"mcp-client-generation-gate-removed-v2-only","canonical_anchor":"mcp-client-generation-gate-removed-v2-only","heading":"MCP connections always use the newer v2 client and the v1 option is gone","tier":"notice","area":"MCP","scope":"individual","heads_up":false,"url":"https:\/\/changelogs.core-directive.com\/v\/2.1.323\/e\/mcp-client-generation-gate-removed-v2-only","release_url":"https:\/\/changelogs.core-directive.com\/v\/2.1.323","markdown":"### MCP connections always use the newer v2 client and the v1 option is gone\n\nClaude Code now always uses its v2 MCP client, and setting `MCP_SDK_GENERATION=v1` only logs a warning\n\n**What**\n\nMCP servers are add-ons that give Claude extra tools. Claude Code talks to them through an MCP client. It used to choose between an older v1 client and the newer v2 client using a switch controlled remotely, which picked v2 unless told otherwise.\n\nThat choice is gone. Claude Code now always uses the v2 client. If you set the environment variable `MCP_SDK_GENERATION=v1`, Claude Code no longer switches back. It logs a warning that this build has only the v2 client, and describes v1 as the one using the older handshake and relaxed sign-in checks.\n\n**Why**\n\nThere is no longer a way back to the v1 client. If you used `MCP_SDK_GENERATION=v1` to work around a problem with an MCP server, that workaround no longer has any effect.\n\n- Flag `tengu_brindle_causeway`: On for this account, and not off by default (read for one account on one subscription tier against v2.1.323; this account: on, anonymous baseline: on, compiled default: not a boolean we can read) These values were read against a different version of Claude Code, so treat them as the nearest reading available instead of one taken on this release.\n- Area: MCP\n- Tier: You'll notice\n- Useful: 2\/5\n- Signal: 1\/5\n- Scope: individual\n- Heads-up: no"}