A background session is a Claude Code session that keeps running apart from your terminal. A helper program running behind the scenes, called a daemon, starts and manages it. Before starting one, Claude Code now checks two more things and refuses with "Couldn't start a background session: ..." plus the detail when either fails:
- The daemon is outdated
- Your sign-in credential is unavailable
Before, the only reasons it gave were a short-lived or stale daemon, a missing working folder, or a daemon it could not reach.
When the environment for the new session sets ANTHROPIC_CONFIG_DIR, Claude Code now prefers to reach the daemon over its direct connection instead of handing off through a file.
A background session started against an old daemon now fails with a clear reason. A custom config folder set with ANTHROPIC_CONFIG_DIR now carries through to the session.