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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 v2.1.239

MCP servers can be put in their own memory cgroup on Linux

Use it now
Useful3 Signal4
MCP Notable not in their notes

On Linux you can force MCP servers into their own memory cgroup with an environment variable.

Feature flag
tengu_mcp_memory_cgroup Off in both readings

The flag server returned off for the account this site reads and for the anonymous baseline. A reading of off cannot rule out a rollout these two readings sit outside of.

This account: off · anonymous baseline: off · compiled default in v2.1.239: on

Read once, for one account on one subscription tier, against v2.1.239. It isn't a statement about your account. What a flag value here can and cannot tell you

CLAUDE_CODE_MCP_MEMORY_CGROUP
What

On Linux, MCP server processes and up to 256 of their discovered child processes can be attached to a dedicated mcp control group so their memory is accounted separately from Claude Code's. Off unless the tengu_mcp_memory_cgroup flag is on (its fallback is false); CLAUDE_CODE_MCP_MEMORY_CGROUP forces it on, and a falsy value or none disables it.

Details
  • Processes spawned before the flag resolves are parked and attached once it does.
  • Reports a tengu_mcp_cgroup event with status enabled or disabled, plus mcp_memory_cgroup failure reasons.
Evidence

tengu_mcp_memory_cgroup

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

Related

Other releases about the same thing. Found by shared names or similar wording; neither means one caused the other.

See this entry in the whole of v2.1.239 →