Claude Code 2.1.276 Fixes Proxy Gateway 400 Regression

Anthropic shipped Claude Code CLI 2.1.276 just under six hours after 2.1.275, fixing a regression that caused all requests through a proxy or gateway (via ANTHROPICBASEURL) to fail with 400 errors; the update adds about 440 tokens to the system prompt.

2026-09-18 ~ 2026-09-18 · 3 related posts

• Claude Code 2.1.276 fixes 400 errors for all requests when ANTHROPIC_BASE_URL uses a proxy — ClaudeCodeLog · 2026-09-18
• Claude Code 2.1.276 by the numbers: shipped in under 6 hours, +440 prompt tokens — ClaudeCodeLog · 2026-09-18

1 near-duplicate retellings: ClaudeCodeLog