Unclear The finding does not say which tools are actually marked as detach-capable versus self or never, or when background results become visible to the user.
Many built-in tools — including WebFetch, WebSearch, Bash, Task, PowerShell, MCP (Model Context Protocol) tools, and various read-only lookup tools — now carry a backgrounding property set to one of three values: "detach", "self", or "never". Tools without a value default to "never". A new internal check looks at whether a tool's backgrounding is "detach" to decide if that tool call is allowed to keep running in the background, with its result delivered later through a separate message once it finishes.
This lays the groundwork for certain tools to run in the background instead of blocking the conversation while they complete, letting Claude Code (and the user) continue working while a long-running tool call finishes elsewhere.
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 does not say which tools are actually marked as detach-capable versus self or never, or when background results become visible…
Anthropic's documentation has since written up backgrounding, on Agent SDK reference - TypeScript.