What it is
A long-running tool call can now be moved to the background instead of blocking when a new message comes in
Not Anthropic's. This is the line from the earliest changelog entry here that named it, v2.1.277.
Presence across releases
1Build by build
3One row per release since the first build this name was read out of. Absent means the build was read and the name was not in it, never mined means no bundle for that release was ever archived, and a declared type or a default is only ever what that release's own bundle stated.
First cited
1The earliest release whose published evidence quoted tengu_tool_detach was v2.1.277, 18 Sep 2026. That is the oldest release this project wrote about it, so it is a floor on the name's age and not the release that introduced it. It is not a presence reading: which builds carried the name is the table above.
Gate readings
1| Release | Resolved | This account | Anonymous | Compiled default |
|---|---|---|---|---|
| v2.1.277 read on another version | Not enough to say | no value returned | no value returned | on |
Two arms, because they disagree: this account is the one account this site reads and anonymous is a baseline with no identity attached. A reading says nothing about your account, and off cannot rule out a rollout both readings sit outside of. What these readings can and cannot show.
Names beside it
Every feature flag in the inventory starting tengu_tool, up to twelve of them.
tengu_tool_cgroupOn Linux you can cap memory for shell commands so a runaway process cannot eat your machine. never mined
tengu_tool_cgroup_exclude_classesMemory limits now reach npm, git, tmux, LSP, MCP and hooks, but everything except Bash is excluded. never mined
tengu_tool_cpu_by_phaseRemote sessions now report per-phase CPU usage split between CLI and tool subprocesses. never mined
tengu_tool_memory_cgroupOn Linux you can cap memory for shell commands so a runaway process cannot eat your machine. v2.1.233
tengu_tool_pearA new capability gate tied to the opus_5_5_prompt_bundle flag can unlock certain model features, and a tool_pear beta header now depends on a flag not yet read for this account v2.1.138
tengu_tool_result_dedupNo description from anybody. never mined
tengu_tool_result_pairing_repairedTool-result repair now detects and reports 'misplaced' tool results in debug output never mined
tengu_tool_result_persistenceNo description from anybody. never mined
tengu_tool_schema_sizesA new event breaks down tool schema sizes by category, deduplicated and capped at 512 hashes. never mined
tengu_tool_search_mode_decisionNo description from anybody. never mined
tengu_tool_search_unsupported_modelsNo description from anybody. v2.1.138
tengu_tool_use_diff_computedWriting over a very large file skips diff computation, so it no longer stalls. never mined
Read out of the published npm bundle release by release, and out of Anthropic's own documentation as this site captured it. Nothing on this page is a description anybody here wrote about what the feature flag does. All feature flags.