Claude Code API 400 'cache_control cannot be set for empty text blocks' Bricks Sessions

What this error means

cache_control cannot be set for empty text blocks is a Claude Code failure pattern reported for developers trying to fix claude code session crash caused by 400 error on cache_control with empty text blocks. Based on the imported evidence, treat this as a tool-specific troubleshooting page rather than a generic API error.

Why this happens

Multiple users report Claude Code Cloud sessions crashing with API Error 400 messages.248.content.3.text: cache_control cannot be set for empty text blocks. Sessions become unrecoverable. Happens in both long (>200 messages) and new (~25 messages) sessions, triggered by pasting screenshots.

Common causes

• Claude Code sessions become permanently unusable once this error occurs. The agent constructs request payloads with empty text content blocks that have cache_control markers, which the Anthropic API rejects. Users on paid Max tier plans lose active coding sessions with no recovery path.
• Multiple users report Claude Code Cloud sessions crashing with API Error 400 messages.248.content.3.text: cache_control cannot be set for empty text blocks. Sessions become unrecoverable. Happens in both long (>200 messages) and new (~25 messages) sessions, triggered by pasting screenshots.

Quick fixes

1. Confirm the exact error signature matches cache_control cannot be set for empty text blocks.
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/58987

Evidence note: Multiple users report Claude Code Cloud sessions crashing with API Error 400 messages.248.content.3.text: cache_control cannot be set for empty text blocks. Sessions become unrecoverable. Happens in both long (>200 messages) and new (~25 messages) sessions, triggered by pasting screenshots.

Related errors

• Claude Code API 400 text content blocks must be non-empty
• Claude Code session recovery after API errors

FAQ

What should I check first?

Start with the exact cache_control cannot be set for empty text blocks 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 cache_control cannot be set for empty text blocks.