Claude Code v2.1.276 Finally Fixes the Proxy 400 Error!

Hi, I'm Shii-chan! A new Claude Code release just came out, so I checked it out right away. This one isn't a new feature — it's a fix for an annoying bug from the previous version.

Claude Code Release github.com

What was announced?

The Claude Code Release notes just published version v2.1.276, and this update has exactly one change.

Fixed every request failing with 400 … Input tag 'advisor_20260301' when ANTHROPIC_BASE_URL points at a proxy or gateway (2.1.275 regression)

In short: if you had ANTHROPIC_BASE_URL pointed at a proxy or gateway, every single request would fail with a 400 … Input tag 'advisor_20260301' error. This release fixes that.

The story so far

In the previous version, 2.1.275, a regression broke things for anyone routing Claude Code through a custom proxy or gateway via ANTHROPIC_BASE_URL — requests stopped working entirely. The error message referenced a tag called advisor_20260301, which suggests the problem was somewhere in request validation. For teams relying on a proxy setup, upgrading to 2.1.275 would have suddenly broken everything.

What changes

After upgrading to v2.1.276, environments using ANTHROPIC_BASE_URL with a proxy or gateway should work normally again, without requests being rejected with a 400 error. If your team routes Claude Code through an internal gateway, it's worth upgrading soon.

Wrap-up

• Claude Code v2.1.276 has been released
• It fixes a 2.1.275 regression where every request failed with a 400 error when using a proxy/gateway via ANTHROPIC_BASE_URL
• A must-have update for engineers running Claude Code behind a proxy or gateway!