Bedrock, Vertex AI, and universal structured outputs support

Braintrust has expanded its support to Amazon Bedrock and Google Vertex AI, offering a unified interface for developers to access more models. The platform now handles structured output handling across most providers, including those that don't natively support it, ensuring reliable JSON responses. This improvement eliminates the need for additional prompt engineering or post-processing, making it simpler to test different models for specific use cases. Additionally, Braintrust has simplified model selection in its playground by grouping models by provider and family, and made several other updates to enhance the developer experience, including improved support for custom headers and stable configurations.