AWS Bedrock not working in Agents with MCP

[Micheletto]

What happened?

When using an Agent with an MCP configured, for example the Elevenlabs official MCP server, and Claude 4 in AWS Bedrock, all requests fail with the following red box error: Operation aborted The model returned the following errors: Malformed input request, please reformat your input and try again. Switching to Anthropic as the model provider resolves the problem.

Version Information

e370a87

Steps to Reproduce

1. Configure an MCP server (Eleven Labs).
2. Create an Agent.
3. Add the MCP server tools.
4. Choose AWS Bedrock as the provider.
5. Start a conversation.

What browsers are you seeing the problem on?

Chrome

Relevant log output

This is the associated error that LibreChat throws: [api/server/controllers/agents/client.js #sendCompletion] Operation aborted The model returned the following errors: Malformed input request, please reformat your input and try again.

Screenshots

Code of Conduct

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

[danny-avila]

Updating Instructions (docker):
https://www.librechat.ai/docs/local/docker#update-librechat

[danny-avila]

@Micheletto I was able to reproduce this and seems Bedrock is requiring max_tokens to be set for anthropic models:

https://docs.aws.amazon.com/bedrock/latest/userguide/model-parameters-anthropic-claude-messages-request-response.html

But this is only really "required" if tools are also added.

When using an agent, it omits any model parameters you didn't set, while with non-agent, it always sets a default max_tokens for anthropic models.

I will implement something to get around this, but for now you can explicitly set max output tokens to make it work:

[Micheletto]

Thanks! @danny-avila, that worked for me.