Anthropic API Prompt Caching Writes Extra Cache Entries Billing 1.25x for Unread Tokens

What this error means

cache_creation=1416 cache_read=2227 uncached_input=8 — server writes additional cache entries past explicit cache_control breakpoint is a Anthropic API failure pattern reported for developers trying to fix unexpected cache write charges on anthropic api when using explicit cache_control breakpoint. Based on the imported evidence, treat this as a tool-specific troubleshooting page rather than a generic API error.

Why this happens

GitHub issue #1547 on anthropic-sdk-python: server writes additional cache entry inside user content on warm calls despite only one explicit cache_control marker. Billed at 1.25x for tokens never read back. Reproducible on SDK 0.102.0 and 0.79.0, confirming server-side behavior. Direct billing impact for paying Anthropic API users.

Common causes

• GitHub issue #1547 on anthropic-sdk-python: server writes additional cache entry inside user content on warm calls despite only one explicit cache_control marker. Billed at 1.25x for tokens never read back. Reproducible on SDK 0.102.0 and 0.79.0, confirming server-side behavior. Direct billing impact for paying Anthropic API users.

Quick fixes

1. Confirm the exact error signature matches cache_creation=1416 cache_read=2227 uncached_input=8 — server writes additional cache entries past explicit cache_control breakpoint.
2. Check the Anthropic API 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/anthropic-sdk-python/issues/1547

Evidence note: GitHub issue #1547 on anthropic-sdk-python: server writes additional cache entry inside user content on warm calls despite only one explicit cache_control marker. Billed at 1.25x for tokens never read back. Reproducible on SDK 0.102.0 and 0.79.0, confirming server-side behavior. Direct billing impact for paying Anthropic API users.

Related errors

• Anthropic API

FAQ

What should I check first?

Start with the exact cache_creation=1416 cache_read=2227 uncached_input=8 — server writes additional cache entries past explicit cache_control breakpoint text and the smallest action that reproduces it.

Can I ignore this error?

No. Treat it as a failed Anthropic API 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 cache_creation=1416 cache_read=2227 uncached_input=8 — server writes additional cache entries past explicit cache_control breakpoint.