ANTHROPIC_BASE_URL

What it is

ANTHROPIC_BASE_URL is the environment variable that points Claude Code at a custom API endpoint. It routes requests through a proxy or gateway that implements the Anthropic Messages protocol.

Source: Anthropic, Claude Code environment variables, read 2026-09-25

Source: Anthropic, Claude Code LLM gateway, read 2026-09-25

Source: RunInfra, Claude Code configuration, read 2026-09-25

Why it moves cost and latency

Changing the endpoint does not choose a model or configure authentication. ANTHROPIC_AUTH_TOKEN supplies a Bearer token, while ANTHROPIC_DEFAULT_SONNET_MODEL, ANTHROPIC_DEFAULT_OPUS_MODEL, and ANTHROPIC_DEFAULT_HAIKU_MODEL select provider model IDs for those aliases. A non-first-party host disables MCP tool search by default; enable ENABLE_TOOL_SEARCH=true only if the proxy forwards tool_reference blocks.

What it looks like in practice

RunInfra's documented environment lines are 'export ANTHROPIC_BASE_URL="https://api.runinfra.ai"' and 'export ANTHROPIC_AUTH_TOKEN="$RUNINFRA_GATEWAY_KEY"', with the workspace key loaded into RUNINFRA_GATEWAY_KEY. Use the bare host because Claude Code appends /v1, and follow the linked configuration guide to set the main, alias, and subagent models.

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