Incident Report: Invalid beta headers with Claude Code

LiteLLM incident report. Published 2026-02-16.

Date: February 13, 2026 Duration: ~3 hours Severity: High Status: Resolved

Note: This fix will be available starting from v1.81.13-nightly or higher of LiteLLM.

Summary

Claude Code began sending unsupported Anthropic beta headers to non-Anthropic providers (Bedrock, Azure AI, Vertex AI), causing invalid beta flag errors. LiteLLM was forwarding all beta headers without provider-specific validation. Users experienced request failures when routing Claude Code requests through LiteLLM to these providers.

• LLM calls to Anthropic: No impact.
• LLM calls to Bedrock/Azure/Vertex: Failed with invalid beta flag errors when unsupported headers were present.
• Cost tracking and routing: No impact.

Background

Anthropic uses beta headers to enable experimental features in Claude. When Claude Code makes API requests, it includes headers like anthropic-beta: prompt-caching-scope-2026-01-05,advanced-tool-use-2025-11-20. However, not all providers support all Anthropic beta features.

Before this incident, LiteLLM forwarded all beta headers to all providers without validation:

Requests succeeded for Anthropic (native support) but failed for other providers when Claude Code sent headers those providers didn’t support.

Root cause

LiteLLM lacked provider-specific beta header validation. When Claude Code introduced new beta features or sent headers that specific providers didn’t support, those headers were blindly forwarded, causing provider API errors.

Remediation