Code Mode in Claude Code: turn it on and every request costs fewer tokens

TL;DR Start with CLAUDE_CODE_EXPERIMENTAL_CODE_MODE=1 claude, accept the notice and check that /status says Code Mode: on. On v2.1.323, with the same setup, every request went out with about 14,000 fewer tokens of context. The trade: that session can only be resumed with Code Mode on, and it loses Remote Control, Chrome and the background.

Code Mode is the experimental mode that shipped in v2.1.323 on November 12: Claude stops calling Read, Bash or Edit one at a time and writes JavaScript that calls them. The script runs locally, and what comes back into the conversation is what it returns or logs, not everything it read along the way. It ships off: either you turn it on, or it doesn't exist for you.

What changes on a real task

The same request in two Opus 5.5 sessions at medium, identical except for Code Mode: an orders/ folder with 40 daily JSON files, and the question of which three customers spent the most on paid orders. With Code Mode on, this is the script Claude used to get the totals:

const t = {};
for (const f of files) for (const o of JSON.parse(await file('orders/' + f).text()))
  if (o.status === 'paid') t[o.customer] = (t[o.customer] || 0) + o.amount;
Object.entries(t).map(([c, v]) => [c, Math.round(v * 100) / 100]).sort((a, b) => b[1] - a[1])

It read all 40 files inside the script, and the only thing that came back into the conversation was the list of eight customers with their totals. files came from an earlier script: variables survive from one script to the next.

The saving didn't come from fewer turns: without Code Mode, Claude wrote a script too, in Python through Bash. It came from the fixed context. In Code Mode the model gets two tools, REPL (runs the JavaScript) and Poll (collects results), and the rest reach it as JavaScript functions described inside REPL, in a shorter form. That difference rides along on every request: the more requests a task makes, the more tokens it adds up to, though after the first one they are mostly cache reads, which cost less. One run each is not a benchmark, and on this one Code Mode was slower.

You can check it in your own session with /context after the first reply (before it, the Code Mode figure is an underestimate):

Without Code Mode   ⛁ System tools: 24.6k tokens (2.5%)
With Code Mode      ⛁ System tools: 11.1k tokens (1.1%)

How to turn it on

1. Start with the variable

CLAUDE_CODE_EXPERIMENTAL_CODE_MODE=1 claude

To keep it on, put it in the env block of ~/.claude/settings.json. The project's .claude/settings.json won't do: Claude Code ignores it there without a word. Use 1 as the value.

2. Accept the notice

The first time, a dialog titled Code Mode (experimental) opens with the focus on No, start without it. Move down to Yes, turn on Code Mode and press Enter. What it warns you about, in short: it's an experiment that can change or disappear in any release, a session you start in Code Mode can only be resumed with Code Mode on (cloud sessions and the Claude apps can't continue it), and in auto mode the safety check reads each script once before it runs, not each tool the script then calls. If you work in auto mode, that's the change that matters. Say yes and it's saved, so it won't ask again; say no and it asks on every launch while the variable is set.

3. Check that it's on

This line shows at startup:

⚠ Code Mode (experimental) is on · this session can be resumed only with Code Mode on

And /status says so, with where it came from:

Code Mode:              on (experimental) · CLAUDE_CODE_EXPERIMENTAL_CODE_MODE in the shell environment

Inside the session, the screen summarizes the work as usual (Read 40 files, listed 1 directory). Press ctrl+o to see each script as a Code(...) entry with the tools it called underneath.

4. To turn it off, remove the variable from wherever you set it, or start with CLAUDE_CODE_EXPERIMENTAL_CODE_MODE=0 in the shell, which wins over settings.json.

What you give up while it's on

This is what you get when you resume a Code Mode session without the variable:

This session was started in Code Mode (experimental), which is off, so it can't be resumed.
To resume it, run:
  CLAUDE_CODE_EXPERIMENTAL_CODE_MODE=1 claude --resume 4a4353fb-1b39-4123-bfa0-25ea4278401e

When it won't turn on

At startup you get Code Mode (experimental) isn't available: plus the reason, and the session starts with the usual tools. The ones you're likely to hit:

Official docs: Changelog, v2.1.323. The page it links to, code-mode, still answered 404 on November 13.

Tested with Claude Code v2.1.323 on Linux, on November 13, 2026.