Error in communicating with Amazon Bedrock in Agents

[Micheletto]

What happened?

The following error occurs in Agents when using Claude Sonnet 4 and Amazon Bedrock as the provider:
field[contentBlockIndex] already exists in this message chunk and value has unsupported type.

Version Information

0bf7089

Steps to Reproduce

1. Create an Agent
2. Select Amazon Bedrock as the provider
3. Use anthropic.claude-sonnet-4-20250514-v1:0
4. Enable a tool
5. Make a request that requires multiple tool calls

What browsers are you seeing the problem on?

Chrome

Relevant log output

The error output is: field[contentBlockIndex] already exists in this message chunk and value has unsupported type.

It appears to be LangChain related.

Screenshots

No response

Code of Conduct

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

[danny-avila]

It's a common stdout that the upstream dependency prints but as you can see, it doesn't actually cause any issues:

[Micheletto]

@danny-avila Is that stopping the agent from providing updates between tool calls? We've noticed that when using Anthropic directly there are updates from the agent about what it's doing. But when using Bedrock, there are none.

[mbochneak]

feedback, provided by the llm, intended for the user, is not being seen by the user, on aws bedrock using claude 4.

In long agentic processes, for example, using Anthropic endpoint, it will provide feedback like "I didn't succeed with this tool call because X, I will try the alternative tool", written inline in between tool responses. This is not seen by the user when using aws bedrock (claude 4 latest), is correctly seen by user when using Anthropic endpoint directly (claude 4 latest).

aws and anthropic seem to use slightly different parameters and spawn prompts. we have found we need to test thoroughly on all endpoints, or there will be unpredictable behavior. non-developer users cannot do this now, so we're really interested in a fix. (also interested in being educated if the conclusions are incorrect!)

Thanks as always for your work on this, librechat 4ever.