Unclear The finding doesn't say what "self" backgrounding means in practice or which tool uses it.
What
Tool definitions now carry a backgrounding field that controls whether a call to that tool can be moved to the background while it's still running, rather than blocking the conversation until it finishes. The possible values are "never", "self", and "detach".
- Most built-in tools, including
ExitPlanMode,KillShell,WebFetch,WebSearch,PushNotification,RunWorkflow,FetchInboxMessage,ReadMcpResource(Dir), scheduled-prompt tools,Edit,NotebookEdit,Read,Glob,TodoRead/TodoWrite,SendMessage,Bash,Task,mcptools, and self-hosted-runner tools, are explicitly set to"never". - Tools that don't set the field default to
"never"as well. - At least one tool is set to
"self".
A helper resolves the effective value, applying the default when a tool doesn't specify one.
Why
This gives Claude Code a consistent, explicit way to know which tool calls are safe to move to the background and which must always block, which matters for features that let long-running tool calls detach without disrupting tools that shouldn't be interrupted or backgrounded.
The entry above is what we published on the day. These lines were added later, as Anthropic's own pages caught up, and they sit beside the original rather than replacing it.
Setting [`CLAUDE_CODE_DISABLE_BACKGROUND_TASKS=1`](/docs/en/env-vars#variables) or running in [bare mode](/docs/en/headless#start-faster-with-bare-mode) disables auto-backgrounding along with the rest of the background task functionality, …tools-reference see the edit
For a subagent task, the `summary` field carries a model-generated progress summary and is populated only when [`agentProgressSummaries`](#options) is enabled. For a [backgrounded MCP tool call](/docs/en/mcp#automatic-backgrounding-of-long…agent-sdk/typescript see the edit
The finding doesn't say what "self" backgrounding means in practice or which tool uses it.
Anthropic's documentation has since written up backgrounding, on Agent SDK reference - TypeScript.