MCP servers can opt out of automatic backgrounding with disableAutoBackground

What

MCP (Model Context Protocol) servers are outside programs that give Claude extra tools. Normally, a tool call that runs long is moved to a background task so the turn can continue. A new optional per-server setting, disableAutoBackground, turns that off for one server.

• When true, Claude Code never moves that server's calls to the background on its own, neither after the auto-background delay nor early when a priority "now" message arrives. Instead, a "now" message interrupts the turn and ends the call. Otherwise the turn waits for the call's own result, up to the server's timeout.
• For an sdk type server that sets it, the auto-background delay is 0 (no auto-background), and this is checked before CLAUDE_CODE_MCP_AUTO_BACKGROUND_MS is looked at.
• It is read once, when the server is first registered, from initialize, mcp_set_servers or --mcp-config.
• SDK server settings, covering timeout and disableAutoBackground, are now parsed together. An invalid field is ignored with a log naming that field.
• If a server is already registered, different settings in a later request, including through setMcpServers, are ignored with a message saying to remove and re-add the server. Before, only a changed timeout was checked and warned about.

Why

It is meant for servers whose calls wait on a person, such as approval or question servers, so Claude does not move on while you are still answering. To change the setting for a running server, remove it and add it again.