Worked on stabilizing the Anthropic API integration within the pydantic/pydantic-ai repository, focusing on improving reliability and reducing unnecessary API usage. Addressed a critical issue by implementing a conditional check in Python to prevent empty user messages from being sent to the Anthropic API, which helped lower costs and avoid wasted calls. Enhanced the testing framework by adding regression tests and an HTTP cassette using YAML, ensuring the fix remains robust against future changes. Expanded overall test coverage for Anthropic interactions, enabling earlier detection of edge cases and contributing to a more resilient and cost-effective API integration workflow.