Resuming a session that is running in the background now opens…

What

A background session is a Claude Code conversation that keeps running without a terminal window attached to it. Before, choosing one in /resume or with claude --resume stopped with a message saying the session was still running, and told you to run claude attach or claude stop. Now Claude Code tries to open it for you:

The session is opened as if you had run claude attach <jobId>, and Claude Code prints "Opening ..., running in the background".
If you gave a prompt, it is first sent to that session so it runs as the next turn.
Before handing over, Claude Code checks that the background session is running the same Claude Code build. If it is not, you get an ESKEW error.
This needs an interactive terminal for both input and output. It does not happen with conflicting flags such as an --output-format other than text.
The path sits behind tengu_resume_open_live_bg, whose built-in fallback is on when the server sends no value.

If opening fails or a launch prompt is still pending, a screen explains why. It now shows the session title followed by " is running in the background". It also says whether your prompt was queued, not confirmed, or not sent, and still suggests claude attach, claude stop and claude --resume ... --fork-session. A separate message tells you when your latest conversation is running in the background. It points to claude agents or claude --resume, and adds --fork-session when forking into a new copy is possible.

Why

Resuming a busy background session no longer dead-ends, and a prompt you typed is not silently lost. You are told what happened to it.

Read from

Names in the bundleclaude attach

Feature flag

tengu_resume_open_live_bg Not enough to say

Nothing here resolved what this flag was doing on this version, so nothing here should be read as on or off.

This account: no value returned · anonymous baseline: no value returned · compiled default in v2.1.285: on

These values were read against a different version of Claude Code, so treat them as the nearest reading available instead of one taken on this release.

Read once, for one account on one subscription tier, against v2.1.285. It isn't a statement about your account. What a flag value here can and cannot tell you

How sure we are

Something disagreesSomething we can check disagrees with this entry, or the writer said they could not settle it.

The writer flagged doubtWhich commands lead here, and which terminal conditions are needed, are not known.

Anthropic's release notes agreeFixed claude attach, logs, stop, respawn and rm starting a new session with the command name as its prompt when options came before it, such…

The name it cites is new in this buildNew in this build: tengu_resume_open_live_bg

See this entry in the whole of v2.1.285 →

The build it came inv2.1.285

29 Sep 2026 · 428 entries, this one is #19.

Use it now17
You'll notice286
Nothing to try yet7
Under the hood118

Either side of it

v2.1.284Older

Open the release →

Names in this entry

slash/resume
Resume a conversation by ID or name, or open the session picker. Background sessions appear in the picker marked with bg; one that is still running can't be resumed here, so attach to it from claude agents or stop it there first. Alias: /continue
cli--resume
Resume a specific session by ID or name, or show an interactive picker to choose a session. In place of an ID, you can pass the absolute path to a session's .jsonl transcript file. The picker and name search include sessions that added this directory with /add-dir. When you pass a session ID, Claude Code searches the current project directory and its git worktrees, then every other project on this machine. Before v2.1.223, the ID search covered only the current project directory and its git worktrees. Background sessions appear in the picker marked with bg
flagtengu_resume_open_live_bg
--resume on a session running in the background now attaches to it and hands over your prompt instead of refusing
cli--fork-session
When resuming, create a new session ID instead of reusing the original (use with --resume or --continue)

Anthropic's note

Upstream's own release notes for v2.1.285 name something this entry names, so the two are probably about the same change. Probably: the pairing is made on a shared name rather than on the words around it.

Fixed claude attach, logs, stop, respawn and rm starting a new session with the command name as its prompt when options came before it, such as from a shell alias

Is this right?

Other releases about the same thing. Found by shared names or similar wording; neither means one caused the other.

v2.1.221 claude attach now measures time-to-interactive
Both mention attach
v2.1.247 claude attach tells you whether the terminal host died or just never answered
Both mention attach
v2.1.257 New CLI messaging when resuming a session that's already running
Both mention attach