Anthropic web_search causes "text content blocks must contain non-whitespace text" error on follow-up messages

[B-ai-P]

What happened?

Environment

• Deployed on Hugging Face Spaces using LibreChat Docker image.
• Model provider: Anthropic API
• Feature: Web Search tool enabled.

Description

When using an Anthropic model (Claude) with the Web Search tool enabled, the first message works fine — the AI performs a web search and returns a proper response. However, any follow-up message in the same conversation fails with the following API error:

messages: text content blocks must contain non-whitespace text

Observed behavior

• If Web Search remains ON, the conversation cannot continue at all — every subsequent message throws the same error.
• If Web Search is turned OFF, the conversation resumes normally, but Web Search can no longer be re-enabled in that conversation. Toggling it back on immediately reproduces the same error.
• This effectively makes Web Search a one-shot / single-use feature per conversation, forcing users to start a new session every time they need to search again.

Expected behavior

• After a web search response, follow-up messages should work normally.
• Users should be able to toggle Web Search on/off freely within the same conversation without breaking it.

Suspected cause

The Anthropic API response for web search typically includes empty text blocks alongside server_tool_use and web_search_tool_result blocks. When LibreChat sends the conversation history back to the Anthropic API on the next turn, these empty text blocks are not filtered out, causing the API to reject the request.

Version Information

• Deployment: Hugging Face Spaces (Docker)
• LibreChat image: ghcr.io/danny-avila/librechat-dev:latest
• Model provider: Anthropic API
• Model: Claude (Sonnet / Opus)

Steps to Reproduce

1. Deploy LibreChat on Hugging Face Spaces (Docker).
2. Select an Anthropic model (Claude).
3. Enable the Web Search tool in the conversation.
4. Send a message that triggers a web search (e.g., "What's the latest news about X?").
5. Wait for the AI to respond with search results.
6. Send any follow-up message in the same conversation.
7. Observe the error: messages: text content blocks must contain non-whitespace text
8. Disable Web Search → conversation continues normally.
9. Re-enable Web Search → the same error reappears immediately.

What browsers are you seeing the problem on?

Chrome

Relevant log output

API Error:
messages: text content blocks must contain non-whitespace text

Screenshots

Code of Conduct

• I agree to follow this project's Code of Conduct

[danny-avila]

Cannot be reproduced. You didn't specify which version of LibreChat you are using. Try on v0.8.5

[B-ai-P]

Cannot be reproduced. You didn't specify which version of LibreChat you are using. Try on v0.8.5

I found the triggers.

The error occurs in two cases:

1. When Custom Instructions (system prompt) is set in the conversation.
2. When Use Prompt Caching is turned OFF.

I also tested with Thinking turned OFF, but the error still occurs under the above conditions.

Reproduced on both v0.8.5-rc1 (my HF Spaces deploy) and v0.8.5 (official demo site).

Steps:

1. Select Claude + enable Web Search.
2. Either set Custom Instructions, or turn off Prompt Caching.
3. Send a message that triggers a search.
4. Send a follow-up → error.

Hope this helps narrowing it down.

[jona7o]

I saw this error in some instances of the latest LibreChat version.

[danny-avila]

looking into it, thanks

[danny-avila]

Merging a fix here: danny-avila/agents#124

[pnancarrow]

I just updated my org to v0.8.5 and am seeing this broadly when using Web Search. definitely want to patch ASAP