Claude Code

Claude Code reads its base URL and auth token from environment variables, which you point at Gateway’s Anthropic-compatible endpoint. Shared setup: Building with coding agents.

Configure Claude Code

Set these in the shell where you run claude. If you signed in with Anthropic credentials before, run /logout and relaunch.

export MERGE_GATEWAY_API_KEY="mg_..."
export ANTHROPIC_BASE_URL="https://api-gateway.merge.dev/v1/anthropic"
export ANTHROPIC_AUTH_TOKEN="$MERGE_GATEWAY_API_KEY"
export ANTHROPIC_API_KEY=""
export ANTHROPIC_DEFAULT_OPUS_MODEL="anthropic/claude-opus-5"
export ANTHROPIC_DEFAULT_SONNET_MODEL="anthropic/claude-sonnet-5"
export ANTHROPIC_DEFAULT_HAIKU_MODEL="anthropic/claude-haiku-4-5-20251001"

ANTHROPIC_API_KEY must be empty: any value takes precedence over ANTHROPIC_AUTH_TOKEN and bypasses Gateway. Confirm both with /status, then ask for a small code change.

ANTHROPIC_DEFAULT_*_MODEL maps the opus, sonnet, and haiku tiers to Gateway models. Unset, Claude Code sends bare Anthropic IDs such as claude-sonnet-4-6, which Gateway also accepts.

Enable routing

Set a tier to a model alias so its policy picks the model per request:

export ANTHROPIC_DEFAULT_OPUS_MODEL="@alias/coding-heavy"
export ANTHROPIC_DEFAULT_SONNET_MODEL="@alias/coding-heavy"

Keep ANTHROPIC_DEFAULT_HAIKU_MODEL pinned: Claude Code sends background tasks to the haiku tier, and a fixed model keeps them cheap and predictable. default_routing also works here, using the key’s project policy or the organization default.

Gotchas

• The /model picker lists the full Gateway catalog, your organization’s aliases, and default_routing. Gateway prefixes non-Anthropic IDs with claude-code/ so the picker keeps them, then strips it. Models with a 1M-token context window carry a [1m] suffix.
• The Anthropic endpoint has no project_id body field. Scope an organization key with ANTHROPIC_CUSTOM_HEADERS="X-Project-Id: <project-uuid>", or use a project API key.
• Claude Code doesn’t read .env files. Persist settings per project in the env block of .claude/settings.local.json, or in your shell profile.
• Each session is one thread in Logs; to change grouping, see tracing from coding agents

Next steps