How do I disable the 1M context window in Claude Code?

Set CLAUDE_CODE_DISABLE_1M_CONTEXT=1 in the env block of settings.json, or export it in your shell if you run Claude Code in a terminal. The 1M model variants disappear from the model picker and sessions are held to a 200K window. If you only want compaction to happen earlier, set CLAUDE_CODE_AUTO_COMPACT_WINDOW instead and keep the bigger window.

Where do I put environment variables for Claude Code?

Add them under the env key in a settings.json file, which applies every time, in the Mac app and the terminal alike. Use ~/.claude/settings.json for yourself everywhere, .claude/settings.local.json for yourself in one project, and .claude/settings.json only for values the whole team should share. In the Mac app, the local environment editor also reaches your dev server. In a terminal, you can also export them in your shell before running claude.

Why is my Claude Code environment variable being ignored?

Five usual causes. You exported it in your shell profile and opened the Mac app from the Dock, which picks up only PATH and a fixed set of Claude Code variables from that profile. A shell variable was changed after launch, and those are read only at startup. The same variable is set in a settings file, which wins over the shell. A managed setting overrides it. Or it is a variable such as CLAUDE_CONFIG_DIR that project and local settings files are not allowed to set.

Why is Claude Code billing my API key instead of my subscription?

ANTHROPIC_API_KEY is set somewhere, usually in a shell profile. When it is present it takes priority over your Pro or Max login, and in -p mode it is always used. Run unset ANTHROPIC_API_KEY and remove it from your profile to go back to your subscription.

Claude Code Environment Variables: How to Set Them, and the 25 Worth Knowing

Most settings have a variable, and some only have a variable

Environment variables control which model Claude Code uses, which account it bills, where its requests go, how long it waits, and a long list of on/off switches. Many of them overlap with a settings.json key, a CLI flag or a slash command. A few exist only as a variable.

Anthropic's full list runs to well over a hundred entries, most of them for gateways, cloud providers and enterprise setups. This page covers how to set them, which value wins when two places disagree, and the 25 a working practitioner actually reaches for.

Where to set them

In the Mac app

In a settings file, for every session. Add an env block to ~/.claude/settings.json:

json

{
  "env": {
    "BASH_DEFAULT_TIMEOUT_MS": "300000",
    "MCP_TIMEOUT": "60000"
  }
}

Claude Code reads this straight from the file, however you launched it. A running session picks up new and changed values when you save. Removing a line does not unset it until the next launch.

warning

No shell runs over the env block

Values are copied exactly as written. ~ and $HOME stay as literal text, so a path like CLAUDE_CONFIG_DIR needs the full absolute path: "/Users/you/.claude-work".

In the local environment editor, when your dev server needs the value too. Open the environment dropdown in the prompt box, hover over Local, and click the gear icon. Variables saved there are stored encrypted on your Mac and apply to every local session and every preview server the app starts. The env block reaches Claude's sessions only, not your dev server.

note

An export in ~/.zshrc mostly doesn't reach the app

When you open the Mac app from the Dock or Finder, it reads your shell profile only for PATH and a fixed set of Claude Code variables. Anything else you export there is ignored. Use the env block or the environment editor instead, and restart the app after changing PATH.

From the terminal

In your shell, for one terminal session. Set it before you launch claude:

bash

# macOS, Linux, WSL
export BASH_DEFAULT_TIMEOUT_MS=300000
claude

powershell

# Windows PowerShell
$env:BASH_DEFAULT_TIMEOUT_MS = "300000"
claude

To make it permanent, put the export line in ~/.zshrc or ~/.bashrc. Claude Code reads shell variables once at startup, so a change applies the next time you launch it. The env block above works here too.

Which settings file

The file you pick decides who the variable applies to.

"env": { ... }

inside a settings.json file

~/.claude/settings.json
you, in every project
.claude/settings.json
the whole team, committed to git
.claude/settings.local.json
you, in this project only
managed settingswins
everyone in the org, set by an admin

where an env block livesThe same env block means something different in each file. Managed settings override the rest.

File	Applies to
`~/.claude/settings.json`	You, in every project
`.claude/settings.json`	Everyone on the project, committed to git
`.claude/settings.local.json`	You, in this project only. Add it to `.gitignore` if you create it by hand.
Managed settings	Everyone in your organization, deployed by an admin

A personal API key or a machine-specific path belongs in your user file or the local file, never in the committed project file.

Which value wins

Settings file beats shell. When the same variable is in both, the env block value applies in most sessions.
Managed beats everything. A managed settings entry overrides the same variable in user or project settings.
Some files can't set some variables. Project and local settings ignore CLAUDE_CONFIG_DIR and the OpenTelemetry export variables, among others.
Flags and variables vary by feature. --model and /model override ANTHROPIC_MODEL. CLAUDE_CODE_EFFORT_LEVEL goes the other way and overrides --effort and /effort.

You can set a variable in a settings file, but you can't delete one. To cancel a stale variable that a shell profile exports, set it to an empty string, for example "CLAUDE_CODE_USE_VERTEX": "".

On, off, and the odd ones

For switches, 1, true, yes and on turn a feature on, and 0, false, no and off turn it off. A handful only check whether the variable is set at all. For DISABLE_TELEMETRY and CLAUDE_CODE_DISABLE_NONESSENTIAL_TRAFFIC, even 0 counts as on. To turn those back off, unset them.

The 25 worth knowing

Account and model

Variable	What it does
`ANTHROPIC_API_KEY`	Bills an API key instead of your Pro, Max, Team or Enterprise plan, even while you're logged in. In `-p` mode it's always used when present. Run `unset ANTHROPIC_API_KEY` to go back to your subscription.
`CLAUDE_CODE_OAUTH_TOKEN`	Signs in with your claude.ai account without `/login`, for scripts and CI. Generate one with `claude setup-token`.
`ANTHROPIC_MODEL`	Default model for the session. `--model` and `/model` still override it.
`CLAUDE_CODE_SUBAGENT_MODEL`	Default model for subagents that aren't given one another way, such as `haiku`.
`CLAUDE_CODE_EFFORT_LEVEL`	`low`, `medium`, `high`, `xhigh`, `max` or `auto`. Overrides `--effort` and `/effort`.

Context and output

Variable	What it does
`CLAUDE_CODE_DISABLE_1M_CONTEXT`	Set to `1` to hold sessions to a 200K window and hide the 1M model variants. Mostly for compliance setups.
`CLAUDE_CODE_AUTO_COMPACT_WINDOW`	The window, in tokens, that auto-compaction works against: `100000` to `1000000`. Plain digits only. `500k` reads as 500 and gets clamped to the 100K minimum.
`CLAUDE_AUTOCOMPACT_PCT_OVERRIDE`	Compact earlier, at a percentage of that window, such as `50`. It can lower the trigger, never raise it.
`CLAUDE_CODE_MAX_OUTPUT_TOKENS`	Cap on output per request. Raising it leaves less room before auto-compaction kicks in.
`MAX_THINKING_TOKENS`	Fixed thinking budget. `0` turns thinking off on the API, except on Opus 5.5, Sonnet 5.5, Haiku 5.5 and Fable, where it can't be turned off.
`CLAUDE_CODE_DISABLE_AUTO_MEMORY`	`1` stops Claude from creating or loading auto memory files.

Timeouts and limits

Variable	Default	What it does
`BASH_DEFAULT_TIMEOUT_MS`	120000 (2 min)	How long a foreground shell command runs before it's stopped
`BASH_MAX_TIMEOUT_MS`	600000 (10 min)	The longest timeout Claude may ask for on one command
`API_TIMEOUT_MS`	600000 (10 min)	How long to wait on an API request. Raise it on slow networks or proxies.
`MCP_TIMEOUT`	30000 (30 s)	How long an MCP server gets to start
`MAX_MCP_OUTPUT_TOKENS`	25000	The largest MCP tool response Claude accepts. A warning shows past 10,000.

If your test suite takes four minutes, BASH_DEFAULT_TIMEOUT_MS is the one that has been killing it at two.

Network, privacy and updates

Variable	What it does
`ANTHROPIC_BASE_URL`	Sends requests through a proxy or gateway. On a non-Anthropic host, MCP tool search turns off by default.
`HTTPS_PROXY`	HTTPS proxy for all network connections
`DISABLE_TELEMETRY`	Opts out of telemetry. Events never include your code, file paths or commands. Any non-empty value counts.
`CLAUDE_CODE_DISABLE_NONESSENTIAL_TRAFFIC`	One switch for auto-updates, telemetry, error reporting, `/feedback` and release notes
`DISABLE_AUTOUPDATER`	Stops background updates. `claude update` still works by hand.
`DISABLE_UPDATES`	Blocks every update, including `claude update`. For teams that ship Claude Code through their own channel.

Setup

Variable	What it does
`CLAUDE_CONFIG_DIR`	Moves the config folder from `~/.claude`. Handy for two accounts side by side, for example `alias claude-work='CLAUDE_CONFIG_DIR=~/.claude-work claude'`.
`CLAUDE_CODE_SHELL`	The shell for the Bash tool. Must be a bash or zsh binary. fish isn't supported.
`CLAUDE_CODE_PROMPT_CACHE_TTL`	`5m` or `1h` cache lifetime for your main conversation. See prompt caching.

Common questions

How do I disable the 1M context window?

Set CLAUDE_CODE_DISABLE_1M_CONTEXT=1. Sessions are held to 200K. If you only want compaction to fire sooner, set CLAUDE_CODE_AUTO_COMPACT_WINDOW instead and keep the bigger window.

Why is my variable being ignored?

Usually one of five things: you exported it in ~/.zshrc and opened the Mac app from the Dock (use the env block instead), you changed a shell variable after launching, a settings file sets the same one and wins, a managed setting overrides it, or it's a variable that project and local files aren't allowed to set.

Why is Claude Code billing my API key?

ANTHROPIC_API_KEY is set, usually in a shell profile, and it takes priority over your login. Unset it.

Permissions: the other half of settings.json
Prompt caching: the TTL variables in context
Headless mode: variables matter most in scripts and CI

Source: Anthropic's environment variables reference, checked October 8, 2026.

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