Unclear It is not clear how the mode is switched on or which environment variable controls it.
What
Claude Code has new code for a REPL mode. In it, Claude writes JavaScript that calls its tools, rather than calling each tool directly. Most of it stays switched off unless the mode is on. What it includes:
- An opt-in dialog that calls the mode "an early experiment" that "may change or be removed in any release".
- A session started in the mode can only be resumed with the mode on.
- When you resume, code that was still running in the background when Claude Code closed shows as "Lost: Claude Code exited before this finished".
- Moving such a session to the cloud is refused.
- Asking a background agent to continue when it has no waiting results reports that there is nothing to wake for.
- The mode can be turned off through a setting or a shell environment variable.
Why
If you try the mode, the sessions you start in it are tied to it: you cannot resume them without the mode on or move them to the cloud, and background work cut short by closing Claude Code is marked as lost.
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It is not clear how the mode is switched on or which environment variable controls it.