How to Use Claude Code Background Sessions with /resume for Long-Running Agentic Workflows

Claude Code 2.1.144 shipped on May 19, 2026 with one of the most-requested quality-of-life improvements for practitioners running long autonomous tasks: /resume now works for background sessions. If you’ve been frustrated by detached runs that disappear from your session picker, this update is for you.

What’s New in 2.1.144

The headline changes in this release are directly aimed at making multi-session, long-running agentic workflows more practical:

  • Background session /resume support — Sessions started in background mode now appear in the /resume picker with a bg badge so you can tell them apart at a glance.
  • Elapsed-duration notifications — When a background subagent finishes, you get an elapsed-time notification so you know exactly how long it ran without having to dig through logs.
  • Per-session /model changes — You can now switch models mid-session without changing the global default. This is useful when you want a lighter or cheaper model for a subtask within a longer workflow.
  • File descriptor exhaustion fix — A long-standing issue where Claude Code would exhaust file descriptors in complex projects is now resolved.
  • macOS background crash fix — Crashes affecting macOS users with Full Disk Access-protected folders in background mode are addressed.
  • 75-second startup hang fixed — An intermittent hang at startup that was affecting a subset of users (primarily on macOS and Linux under high-load conditions) has been resolved.
  • “Extra usage” renamed to “usage credits” — Minor UX cleanup that makes billing-related messaging clearer.

Using Background Sessions

Background sessions in Claude Code let you kick off an autonomous task and detach from the terminal session, so Claude keeps working while you move on to something else.

The core workflow for background sessions looks like this:

  1. Start a session in background mode — According to the official changelog, sessions started with background mode appear in the /resume picker with a bg badge. Refer to the official Claude Code documentation for the exact CLI flag syntax, as flags may change between releases.

  2. Resume a background session — Once you’re ready to reconnect, use /resume inside a new Claude Code session. Background sessions are listed alongside regular sessions, distinguished by the bg badge in the picker.

  3. Check elapsed time — When a background subagent completes a task, you’ll receive an elapsed-duration notification so you can assess how long the autonomous work took.

Why This Matters for Agentic Workflows

The combination of background sessions + /resume is significant for anyone building or using multi-step agentic workflows:

Decoupled execution — Your terminal (and your attention) are no longer blocked while Claude works on a long-running task like a codebase refactor, a test suite run, or a research synthesis.

Resumable state — Previously, background sessions were effectively fire-and-forget. Now they’re first-class resumable sessions, which means you can pause, reconnect, review progress, and continue directing the work.

Per-session model flexibility — The new per-session /model command means you can run your expensive frontier model for planning while letting the background worker execute with a more cost-efficient option.

Operational visibility — Elapsed-duration notifications fill a real gap when you’re managing multiple parallel Claude agents. Knowing that a task finished (and how long it took) without having to poll a terminal tab is meaningful for teams running Claude Code at scale.

The 75-Second Startup Fix

One fix worth calling out separately: the 75-second startup hang. This affected a subset of installations and was particularly noticeable in CI/CD environments and on shared Linux hosts with elevated I/O wait. If you’ve seen Claude Code hang at launch and then eventually recover, updating to 2.1.144 should eliminate that.

What to Do Next

Update to 2.1.144 (or later — 2.1.145 was released the same day with additional improvements). Run claude --version to check your current version.

For full details on background session syntax and the complete list of changes, consult the official Claude Code changelog and the GitHub repository.

Sources

  1. Claude Code Official Changelog — code.claude.com
  2. Claude Code GitHub CHANGELOG.md — github.com/anthropics/claude-code
  3. releasebot.io — Anthropic Claude Code Updates

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