Under the hood
A new helper captures the custom hostname when ANTHROPIC_BASE_URL points somewhere other than Anthropic's API
What
A new helper function returns the hostname from ANTHROPIC_BASE_URL in the specific case where the session is still classified as first-party but the base URL isn't api.anthropic.com, and no unix socket is in use.
Why
This appears to support telemetry or diagnostics around proxy or gateway hosts that don't match Anthropic's usual API address, likely to help identify unrecognized custom endpoints.
Names in the bundleANTHROPIC_BASE_URL
The entry above is what we published on the day. These lines were added later, as Anthropic's own pages caught up, and they sit beside the original rather than replacing it.
Confirmed since
Anthropic's documentation has since written up ANTHROPIC_BASE_URL, on Connect Claude Code to an LLM gateway.
| `400` errors naming `thinking` or `adaptive`, such as `Input tag 'adaptive' found` | The upstream model build doesn't accept adaptive reasoning, which Claude Code requests for Claude 4.6 and later models | Upgrade the gateway's upstream.…llm-gateway-connect see the edit
Something disagreesSomething we can check disagrees with this entry, or the writer said they could not settle it.
The writer flagged doubt
The finding doesn't say what consumes this captured hostname, only that it's produced in this specific case.
Anthropic's documentation agrees
Anthropic's documentation has since written up ANTHROPIC_BASE_URL, on Connect Claude Code to an LLM gateway.