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Reading a new release v2.1.251 Analysing changes · 2/5 Writing the entries · 2/4 steps 470 findings $18.91 so far

DisclaimerUnofficial, and not affiliated with Anthropic. Nearly all of this is read straight out of what ships: npm bundles, captured prompts, published docs. Anthropic's own notes go in verbatim, marked as theirs. The rest is my reading, and every entry carries the strings behind it. If one looks wrong, vote it down and say why.

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Claude Code v2.1.116

MCP Direct Tool Invocation (mcp_call)

What

New mcp_call subtype for MCP requests that enables directly invoking MCP tools via the subprocess MCP client without requiring a model turn.

Details
  • Accepts a fully-qualified MCP tool name (e.g., mcp__server__tool_name)
  • No permission check — the control channel is trusted
  • SDK-type MCP servers are rejected (they are caller-provided and should be invoked directly)
  • Handles URL elicitation for tools that require browser authentication
  • Result content passes through the same processing as model-turn MCP calls (large results may be truncated)
Evidence

MCP call handler (search for "mcp_call") — $K5 at line ~639274

Strings lifted out of the shipped bundle, so the claim above can be checked against them.

See this entry in the whole of v2.1.116 →