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Sweep 01 Oct 2026 · 17:27Z Build v2.1.287 508 read Stable v2.1.285 Latest v2.1.287 Next v2.1.287 Feeds RSS JSON llms.txt llms-full.txt Unofficial
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Claude Code v2.1.287 ·

New environment variable for tool output when Claude Code runs as an MCP server

A new environment variable, CLAUDE_CODE_MCP_SERVE_TOOL_OUTPUT, appears alongside the other MCP server-mode variables

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4Signal: worth watching, 1 to 5
MCPArea: what it touches
New FeaturesKind: in v2.1.287,
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What

Claude Code can run as an MCP server, meaning other programs connect to it using the Model Context Protocol and use its tools. A new environment variable, CLAUDE_CODE_MCP_SERVE_TOOL_OUTPUT, has been added to the same internal list as CLAUDE_CODE_MCP_SERVE_AUTH_TOKEN and CLAUDE_CODE_MCP_SERVE_SETTINGS. An environment variable is a named value set in your shell before a program starts.

Why

The name suggests a new control over tool output in MCP server mode. It sits in a list of sensitive or internal variables, so it is probably not meant for everyday use.

How sure we are
Something disagreesSomething we can check disagrees with this entry, or the writer said they could not settle it.
The writer flagged doubtWhat this variable does, and whether the list it joins hides it from programs Claude Code starts, is not known.

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