ANTHROPIC_BASE_URL
A Claude Code environment variable, read out of the shipped bundle. It has been in the build since v2.1.138, including the newest one read.
Override the API endpoint to route requests through a proxy or gateway. When set to a non-first-party host, MCP tool search is disabled by default. Set ENABLE_TOOL_SEARCH=true if your proxy forwards tool_reference blocks. As of v2.1.196, Remote Control is disabled when this points at a host other than api.anthropic.com, matching its behavior on Amazon Bedrock, Google Cloud's Agent Platform, and Microsoft Foundry
Anthropic's own wording. Read off Environment variables, captured 2026-09-28.
In the changelogs
42Releases whose published page names ANTHROPIC_BASE_URL.
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v2.1.307
Fewer conditions before
ANTHROPIC_AUTH_TOKENis sent to a custom addressClaude Code dropped one check that could stop
ANTHROPIC_AUTH_TOKENfrom being sent to a matchingANTHROPIC_BASE_URLnamed in this entry, found in this entry's text
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v2.1.305
claude plugin evalpasses your session's API key to its test runsWith an API key session,
claude plugin evalnow hands the key to its test runs itself, except on Windows, where you must setANTHROPIC_API_KEYfound in this entry's text
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v2.1.304
Tool search is tried through custom API endpoints and paused for a day if refused
With a custom
ANTHROPIC_BASE_URL, Claude Code now tries MCP tool search and turns it off for a day only if that endpoint refuses itfound in this entry's text, named in this entry
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v2.1.302
Background sessions no longer pass on the withheld-gateway marker
CLAUDE_BG_GATEWAY_WITHHELDis now removed along with other background-session variables, so it does not carry into sessions started from therefound in this entry's text
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v2.1.302
Clear gateway message for background sessions opened from another folder
A background session opened from another folder without its LLM gateway now says so, instead of asking you to log in
found in this entry's text, named in this entry
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v2.1.302
Background sessions in another folder no longer inherit your API base URL
A background session started in a different folder no longer receives
ANTHROPIC_BASE_URL, andCLAUDE_CODE_AUTO_MODE_MODELis now passed onfound in this entry's text
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v2.1.299
Your API key is no longer sent to non-Anthropic hosts when fetching remote settings
If
ANTHROPIC_BASE_URLpoints somewhere other than Anthropic, Claude Code no longer sends your API key when fetching remote settingsfound in this entry's text, named in this entry
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v2.1.299
API key withheld when ANTHROPIC_BASE_URL is not an Anthropic host
On one request path, Claude Code no longer sends your API key to an
ANTHROPIC_BASE_URLthat is not an Anthropic hostfound in this entry's text, named in this entry
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v2.1.296
Managed settings with
allowedProviderscan now setANTHROPIC_BASE_URLautomaticallyWhen managed settings use
allowedProviders, Claude Code may setANTHROPIC_BASE_URLitself unless the managed settings already set itfound in this entry's text, named in this entry
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v2.1.295
Diskless sessions turn off raw API body logging
In a diskless session,
OTEL_LOG_RAW_API_BODIESis ignored and some terminal details are left out of usage datafound in this entry's text
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v2.1.283
New variable pins the remote tools helper to your stored claude.ai login
With
CLAUDE_CODE_REMOTE_TOOLS_PIN_STORED_LOGINset, the serve helper exits with code 78 if its API or sign-in addresses are not Anthropic's ownfound in this entry's text
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v2.1.283
Metrics from cloud sessions can be sent through the session's own connection
In remote sessions, usage metrics can now go to the session's own metrics address, signed with
CLAUDE_CODE_SESSION_ACCESS_TOKENfound in this entry's text
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v2.1.281
CLAUDE_CODE_TETHER_LIVE=true now opts in to several related threads/tether features and bypasses first-party checks
CLAUDE_CODE_TETHER_LIVE=truenow also turns on related threads features and skips some endpoint checksfound in this entry's text
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v2.1.280
code-sign now supports lifecycle-hook processes, not just spawned child sessions
Code-signing now also recognizes lifecycle-hook processes, not just spawned sessions
found in this entry's text
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v2.1.278
New function captures custom ANTHROPIC_BASE_URL host for firstParty sessions
A new helper captures the custom hostname when ANTHROPIC_BASE_URL points somewhere other than Anthropic's API
named in this entry, found in this entry's text
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v2.1.277
New gate function jce for first-party base-URL eligibility
A new internal check gates a capability to first-party accounts using the default API endpoint
found in this entry's text, named in this entry
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v2.1.276
Model-advisor standby model selection now double-checks the base URL is Anthropic's own
Model-advisor's standby model pick now also requires the account to actually be talking to Anthropic's own API
found in this entry's text
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v2.1.266
Cloud gateway sign-in error message shortened
The Cloud gateway sign-in error message dropped its instructions for CLAUDE_CODE_USE_GATEWAY, ANTHROPIC_BASE_URL and ANTHROPIC_AUTH_TOKEN
named in this entry, found in this entry's text
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v2.1.265
Cloud gateway sign-in check reworked with desktop-app-aware error and new required flag
Cloud gateway sign-in check reworked with a clearer error and desktop-app-aware handling
found in this entry's text
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v2.1.260
Direct API client construction now respects ANTHROPIC_BASE_URL as a fallback baseURL
ANTHROPIC_BASE_URL is now actually respected in the direct-API fallback path.
found in this entry's text, named in this entry
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v2.1.257
Gateway model discovery no longer skipped for nonessential-traffic-disabled users
Gateway model discovery now runs even when nonessential traffic is disabled, instead of being skipped.
found in this entry's text, named in this entry
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v2.1.248
Gateway model discovery explains why it skipped, and can use apiKeyHelper
Gateway model discovery can authenticate with apiKeyHelper and logs why it skipped.
named in this entry, found in this entry's text
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v2.1.248
Remote managed settings now show in /status and doctor, with a startup warning on failure
/status and doctor now report remotely-published org settings, with a startup warning on failure.
found in this entry's text
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v2.1.242
Gateway credentials reworked with a TLS pin store
Gateway credential handling reuses pinned entries and gives clearer errors for bad base URLs.
named in this entry, found in this entry's text
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v2.1.232
Tool search says once why it turned itself off
Tool search logs why it disabled itself and refuses entirely against a non-Anthropic base URL.
named in this entry, found in this entry's text
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v2.1.232
Clearer explanations when artifacts are unavailable
When artifacts are unavailable you now get a specific reason, including org policy or custom base URL.
named in this entry, found in this entry's text
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v2.1.229
1M-context models no longer suppressed on custom endpoints
Subscription users on a custom base URL now see the 1M-context model variants again.
named in this entry, found in this entry's text
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v2.1.229
OpenTelemetry can be sent through Anthropic's first-party gateway
Telemetry can route through Anthropic's own gateway, but only under a narrow set of conditions.
named in this entry, found in this entry's text
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v2.1.228
About 220 more environment variables move to the typed registry
About 220 environment variables now parse and validate in one place, including bounds checks.
named in this entry, found in this entry's text
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v2.1.224
Runner management tools require a first-party login and say so
Runner management tools now require
claude loginon Anthropic's API; API keys are rejected.named in this entry, found in this entry's text
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v2.1.223
Gateway model discovery accepts model ids that merely contain claude or anthropic
Gateways whose model ids carry a vendor prefix now show up instead of an empty model list.
named in this entry, found in this entry's text
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v2.1.223
Settings-supplied API and credential env vars are stripped when ANTHROPIC_UNIX_SOCKET is set
When you connect through a unix socket, settings files can no longer override your API keys or endpoint.
named in this entry, found in this entry's text
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v2.1.221
Tool search no longer disabled on Vertex AI
Tool search now runs on Vertex AI instead of being refused outright.
named in this entry, found in this entry's text
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v2.1.219
Remote Control now explains exactly which endpoint setting blocks it
When Remote Control refuses, it now names the exact setting or variable blocking it.
named in this entry, found in this entry's text
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v2.1.199
Request Body Gzip Compression [In Development]
found in this entry's text
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v2.1.166
WebFetch proxy for first-party users
found in this entry's text
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v2.1.138
Advanced Mid-Conversation System Beta Override
found in this entry's text
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v2.1.124
Gateway model discovery for
ANTHROPIC_BASE_URLfound in this entry's text
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v2.1.70
ToolSearch Disabled for Non-First-Party Hosts
found in this entry's text
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v2.0.68
API Base URL Validation
found in this entry's text
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v2.0.36
OpenTelemetry 1P Events
found in this entry's text
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v0.2.56
New Features
found in this entry's text
First cited
7The earliest release whose published evidence quoted ANTHROPIC_BASE_URL was v2.1.70, 6 Mar 2026. That is the oldest release this project wrote about it, so it is a floor on the name's age and not the release that introduced it. It is not a presence reading: which builds carried the name is the table below.
1 further span in the ledger name it. The list above is the earliest first and stops at 6.
Presence across releases
1Build by build
149One row per release since the first build this name was read out of. Absent means the build was read and the name was not in it, never mined means no bundle for that release was ever archived, and a declared type or a default is only ever what that release's own bundle stated.
Read out of the published npm bundle release by release, and out of Anthropic's own documentation as this site captured it. Nothing on this page is a description anybody here wrote about what the environment variable does. All environment variables.