What probably matters to youSection of the release
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.
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.
Confirmed sinceAnthropic's documentation has since written up setMcpServers, on Claude Code changelog.* Fixed an MCP sign-in or reconnect that finishes late in headless and SDK sessions relisting a server set with `setMcpServers()` as your ownchangelogsee the edit
How sure we are
One source agreesOne thing we can check says the same as this entry.
Anthropic's documentation agreesAnthropic's documentation has since written up setMcpServers, on Claude Code changelog.
