Environment Variables

Set in your shell before launching claude, or configure under the env key in settings.json to apply to every session. When an env var and an equivalent settings field both apply, the env var takes precedence (e.g. ANTHROPIC_MODEL overrides the model setting). Changes take effect on the next claude launch.

Authentication

Variable	Description
ANTHROPIC_API_KEY	API key for Anthropic API access. When set, used instead of your Claude subscription even if logged in
ANTHROPIC_AUTH_TOKEN	Custom Authorization header value (prefixed with Bearer )
ANTHROPIC_BASE_URL	Custom API endpoint for proxies or LLM gateways
ANTHROPIC_CUSTOM_HEADERS	Custom headers added to API requests. Format: Name: Value, newline-separated for multiple
ANTHROPIC_BETAS	Comma-separated extra anthropic-beta header values. Works with all auth methods including Claude.ai subscription
ANTHROPIC_WORKSPACE_ID	Workspace ID for workload identity federation when a federation rule covers more than one workspace
CLAUDE_CODE_OAUTH_TOKEN	OAuth access token for Claude.ai authentication. Alternative to /login for SDK and automated environments
CLAUDE_CODE_OAUTH_REFRESH_TOKEN	OAuth refresh token for headless auth. claude auth login exchanges this directly instead of opening a browser. Requires CLAUDE_CODE_OAUTH_SCOPES
CLAUDE_CODE_OAUTH_SCOPES	Space-separated OAuth scopes the refresh token was issued with. Required when CLAUDE_CODE_OAUTH_REFRESH_TOKEN is set
CLAUDE_CONFIG_DIR	Override the configuration directory (default: ~/.claude)

Model Selection

Variable	Description
ANTHROPIC_MODEL	Model to use. Accepts aliases (sonnet, opus, haiku) or full model IDs. Overrides the model setting
ANTHROPIC_DEFAULT_HAIKU_MODEL	Override the Haiku model alias with a custom model ID
ANTHROPIC_DEFAULT_HAIKU_MODEL_NAME	Display name for the Haiku model override
ANTHROPIC_DEFAULT_HAIKU_MODEL_DESCRIPTION	Description for the Haiku model override
ANTHROPIC_DEFAULT_HAIKU_MODEL_SUPPORTED_CAPABILITIES	Capabilities for the Haiku model override
ANTHROPIC_DEFAULT_SONNET_MODEL	Override the Sonnet model alias
ANTHROPIC_DEFAULT_SONNET_MODEL_NAME	Display name for the Sonnet model override
ANTHROPIC_DEFAULT_SONNET_MODEL_DESCRIPTION	Description for the Sonnet model override
ANTHROPIC_DEFAULT_SONNET_MODEL_SUPPORTED_CAPABILITIES	Capabilities for the Sonnet model override
ANTHROPIC_DEFAULT_OPUS_MODEL	Override the Opus model alias (e.g. claude-opus-4-6[1m])
ANTHROPIC_DEFAULT_OPUS_MODEL_NAME	Display name for the Opus model override
ANTHROPIC_DEFAULT_OPUS_MODEL_DESCRIPTION	Description for the Opus model override
ANTHROPIC_DEFAULT_OPUS_MODEL_SUPPORTED_CAPABILITIES	Capabilities for the Opus model override
ANTHROPIC_CUSTOM_MODEL_OPTION	Model ID to add as a custom entry in the /model picker
ANTHROPIC_CUSTOM_MODEL_OPTION_NAME	Display name for the custom model entry
ANTHROPIC_CUSTOM_MODEL_OPTION_DESCRIPTION	Display description for the custom model entry
ANTHROPIC_CUSTOM_MODEL_OPTION_SUPPORTED_CAPABILITIES	Capabilities for the custom model entry
ANTHROPIC_SMALL_FAST_MODEL	DEPRECATED. Use ANTHROPIC_DEFAULT_HAIKU_MODEL instead
ANTHROPIC_SMALL_FAST_MODEL_AWS_REGION	AWS region for the Haiku-class model on Bedrock when ANTHROPIC_DEFAULT_HAIKU_MODEL is also set
CLAUDE_CODE_SUBAGENT_MODEL	Override model for subagents (e.g. haiku)
CLAUDE_CODE_EFFORT_LEVEL	Effort level: low, medium, high, xhigh, max, or auto. Takes precedence over /effort and the effortLevel setting
FALLBACK_FOR_ALL_PRIMARY_MODELS	Any non-empty value triggers fallback to --fallback-model after repeated overload errors on any primary model, not just Opus
CLAUDE_CODE_DISABLE_LEGACY_MODEL_REMAP	Set to 1 to prevent automatic remapping of Opus 4.0 and 4.1 to the current Opus version on the Anthropic API

Cloud Providers

Amazon Bedrock

Variable	Description
CLAUDE_CODE_USE_BEDROCK	Use Amazon Bedrock (1 to enable)
AWS_BEARER_TOKEN_BEDROCK	Bedrock API key for authentication
ANTHROPIC_BEDROCK_BASE_URL	Override the Bedrock endpoint URL. Use for custom regions or when routing through an LLM gateway
ANTHROPIC_BEDROCK_SERVICE_TIER	Bedrock service tier: default, flex, or priority. Sent as X-Amzn-Bedrock-Service-Tier
CLAUDE_CODE_SKIP_BEDROCK_AUTH	Skip AWS auth for Bedrock (e.g. when using an LLM gateway)
CLAUDE_ENABLE_BYTE_WATCHDOG_BEDROCK	Set to 1 to enable byte-level streaming idle watchdog on Bedrock

Bedrock Mantle

Variable	Description
CLAUDE_CODE_USE_MANTLE	Use the Bedrock Mantle endpoint
ANTHROPIC_BEDROCK_MANTLE_BASE_URL	Override the Bedrock Mantle endpoint URL
CLAUDE_CODE_SKIP_MANTLE_AUTH	Skip AWS auth for Bedrock Mantle

Google Vertex AI

Variable	Description
CLAUDE_CODE_USE_VERTEX	Use Google Vertex AI (1 to enable)
ANTHROPIC_VERTEX_BASE_URL	Override the Vertex AI endpoint URL
ANTHROPIC_VERTEX_PROJECT_ID	GCP project ID for Vertex AI requests (overridden by GCLOUD_PROJECT or GOOGLE_CLOUD_PROJECT)
CLAUDE_CODE_SKIP_VERTEX_AUTH	Skip Google auth for Vertex
VERTEX_REGION_CLAUDE_3_5_HAIKU	Region override for Claude 3.5 Haiku on Vertex AI
VERTEX_REGION_CLAUDE_3_5_SONNET	Region override for Claude 3.5 Sonnet on Vertex AI
VERTEX_REGION_CLAUDE_3_7_SONNET	Region override for Claude 3.7 Sonnet on Vertex AI
VERTEX_REGION_CLAUDE_4_0_OPUS	Region override for Claude 4.0 Opus on Vertex AI
VERTEX_REGION_CLAUDE_4_0_SONNET	Region override for Claude 4.0 Sonnet on Vertex AI
VERTEX_REGION_CLAUDE_4_1_OPUS	Region override for Claude 4.1 Opus on Vertex AI
VERTEX_REGION_CLAUDE_4_5_OPUS	Region override for Claude Opus 4.5 on Vertex AI
VERTEX_REGION_CLAUDE_4_5_SONNET	Region override for Claude Sonnet 4.5 on Vertex AI
VERTEX_REGION_CLAUDE_4_6_OPUS	Region override for Claude Opus 4.6 on Vertex AI
VERTEX_REGION_CLAUDE_4_6_SONNET	Region override for Claude Sonnet 4.6 on Vertex AI
VERTEX_REGION_CLAUDE_4_7_OPUS	Region override for Claude Opus 4.7 on Vertex AI. Added in v2.1.111
VERTEX_REGION_CLAUDE_4_8_OPUS	Region override for Claude Opus 4.8 on Vertex AI
VERTEX_REGION_CLAUDE_HAIKU_4_5	Region override for Claude Haiku 4.5 on Vertex AI

Microsoft Foundry

Variable	Description
CLAUDE_CODE_USE_FOUNDRY	Use Microsoft Foundry (1 to enable)
ANTHROPIC_FOUNDRY_API_KEY	API key for Microsoft Foundry authentication
ANTHROPIC_FOUNDRY_BASE_URL	Full base URL for the Foundry resource (alternative to ANTHROPIC_FOUNDRY_RESOURCE)
ANTHROPIC_FOUNDRY_RESOURCE	Foundry resource name. Required if ANTHROPIC_FOUNDRY_BASE_URL is not set
CLAUDE_CODE_SKIP_FOUNDRY_AUTH	Skip Azure auth for Foundry

Claude Platform on AWS

Variable	Description
CLAUDE_CODE_USE_ANTHROPIC_AWS	Use Claude Platform on AWS
ANTHROPIC_AWS_API_KEY	Workspace API key for Claude Platform on AWS, generated in the AWS Console
ANTHROPIC_AWS_BASE_URL	Override the Claude Platform on AWS endpoint URL
ANTHROPIC_AWS_WORKSPACE_ID	Required workspace ID. Sent as the anthropic-workspace-id header on every request
CLAUDE_CODE_SKIP_ANTHROPIC_AWS_AUTH	Skip client-side authentication for Claude Platform on AWS

Multi-cloud

Variable	Description
CLAUDE_CODE_ENABLE_AUTO_MODE	Set to 1 to make auto mode available on Bedrock, Vertex AI, and Foundry. Added in v2.1.158. No effect on Anthropic API
CLAUDE_CODE_PROVIDER_MANAGED_BY_HOST	Set by host platforms managing model provider routing. When set, provider-selection and auth variables in settings files are ignored

Timeouts and Limits

Variable	Description
API_TIMEOUT_MS	API request timeout in milliseconds (default: 600000). Maximum: 2147483647
BASH_DEFAULT_TIMEOUT_MS	Default bash command timeout in milliseconds (default: 120000)
BASH_MAX_TIMEOUT_MS	Maximum bash command timeout in milliseconds (default: 600000)
BASH_MAX_OUTPUT_LENGTH	Maximum characters in bash output before saving to a file and sending the path
MAX_THINKING_TOKENS	Extended thinking token budget. Set to 0 to disable. Ignored on models with adaptive reasoning unless CLAUDE_CODE_DISABLE_ADAPTIVE_THINKING is set
CLAUDE_CODE_MAX_OUTPUT_TOKENS	Max output tokens per response (default: 32,000; up to 128,000 on Opus 5, Sonnet 5, Opus 4.8, and Sonnet 4.6)
CLAUDE_CODE_FILE_READ_MAX_OUTPUT_TOKENS	Override default file read token limit
CLAUDE_CODE_MAX_CONTEXT_TOKENS	Override context window size Claude Code assumes for the active model. Only takes effect when DISABLE_COMPACT is also set
CLAUDE_CODE_MAX_TURNS	Cap the number of agentic turns per session. Equivalent to --max-turns (the flag takes precedence when both are set)
CLAUDE_CODE_MAX_RETRIES	Override the number of retries for failed API requests (default: 10)
CLAUDE_CODE_MAX_TOOL_USE_CONCURRENCY	Maximum read-only tools and subagents executing in parallel (default: 10)
CLAUDE_ASYNC_AGENT_STALL_TIMEOUT_MS	Stall timeout in milliseconds for background subagents (default: 600000)
TASK_MAX_OUTPUT_LENGTH	Maximum characters in subagent output before truncation (default: 32000, max: 160000)
MAX_STRUCTURED_OUTPUT_RETRIES	Retries when model response fails --json-schema validation in non-interactive mode (default: 5)
CLAUDE_CODE_STOP_HOOK_BLOCK_CAP	Maximum consecutive times a Stop hook may block the turn from ending before Claude Code overrides it (default: 8)
CLAUDE_CODE_SESSIONEND_HOOKS_TIMEOUT_MS	SessionEnd hook time budget in ms. Default: 1.5s, raised to the highest configured per-hook timeout up to 60s
CLAUDE_CODE_API_KEY_HELPER_TTL_MS	Credential refresh interval in ms for apiKeyHelper
MCP_TIMEOUT	MCP server startup timeout in ms (default: 30000)
MCP_TOOL_TIMEOUT	MCP tool execution timeout in ms (default: 100000000)

Behavior Control

Variable	Description
CLAUDECODE	Set to 1 in subprocesses Claude Code spawns (Bash/PowerShell tools, tmux sessions, hook commands, status line commands, stdio MCP subprocesses). Use to detect when a script runs inside Claude Code