Claude Code prompt-caching-scope Beta Header Error on Custom API Endpoints — Fix

What this error means

Unexpected value(s) prompt-caching-scope-2026-01-05 for the anthropic-beta header is a Claude Code failure pattern reported for developers trying to fix claude code sending prompt-caching-scope beta header to custom api endpoints that don’t support it. Based on the imported evidence, treat this as a tool-specific troubleshooting page rather than a generic API error.

Why this happens

Claude Code extension v2.1.23 sends prompt-caching-scope-2026-01-05 beta header to custom API endpoints (via ANTHROPIC_BASE_URL) even when enablePromptCaching and useAnthropicBetaHeaders are both set to false. Results in API error on incompatible endpoints.

Common causes

• When Claude Code is configured with ANTHROPIC_BASE_URL pointing to a custom endpoint (proxy, mock server, or alternative provider), it injects the prompt-caching-scope-2026-01-05 beta header even when prompt caching is disabled, causing 400 errors. Developers using custom API gateways encounter this incompatibility.
• Claude Code extension v2.1.23 sends prompt-caching-scope-2026-01-05 beta header to custom API endpoints (via ANTHROPIC_BASE_URL) even when enablePromptCaching and useAnthropicBetaHeaders are both set to false. Results in API error on incompatible endpoints.

Quick fixes

1. Confirm the exact error signature matches Unexpected value(s) prompt-caching-scope-2026-01-05 for the anthropic-beta header.
2. Check the Claude Code account, local tool state, and provider configuration involved in the failing workflow.
3. Compare the failing environment with a known working setup, then change one configuration value at a time.

Platform/tool-specific checks

• Verify the command, editor, extension, or API client that produced the error.
• Compare local settings with CI, deployment, or editor-level settings when the error appears in only one environment.
• Avoid deleting credentials, local model data, or project settings until the failing scope is clear.

Step-by-step troubleshooting

1. Capture the exact error message and the command, editor action, or request that triggered it.
2. Check whether the failure is account/auth, quota/rate, model/provider, local runtime, or deployment configuration.
3. Review the source evidence below and compare it with your environment.
4. Apply one change at a time and rerun the smallest failing action.
5. Keep the working fix documented for the team or deployment environment.

How to prevent it

• Keep provider/tool configuration documented.
• Record non-secret diagnostics such as tool version, provider name, model name, and command path.
• Add a lightweight check before CI or production workflows depend on the tool.

Sources checked

• https://github.com/anthropics/claude-code/issues/21644

Evidence note: Claude Code extension v2.1.23 sends prompt-caching-scope-2026-01-05 beta header to custom API endpoints (via ANTHROPIC_BASE_URL) even when enablePromptCaching and useAnthropicBetaHeaders are both set to false. Results in API error on incompatible endpoints.

Related errors

• Claude Code effort-2025-11-24 beta header error
• Claude Code custom API endpoint incompatible

FAQ

What should I check first?

Start with the exact Unexpected value(s) prompt-caching-scope-2026-01-05 for the anthropic-beta header text and the smallest action that reproduces it.

Can I ignore this error?

No. Treat it as a failed Claude Code workflow until the root cause is understood.

Is this guaranteed to have one fix?

No. The imported evidence supports the troubleshooting path above, but tool behavior can vary by account, plan, version, provider, and local configuration.

How do I know the fix worked?

Rerun the same command, editor action, or request. The fix is working when that action completes without Unexpected value(s) prompt-caching-scope-2026-01-05 for the anthropic-beta header.