During January 2026, Guillaume Vigan focused on backend reliability for the run-llama/llama_index repository, addressing a critical issue in Anthropic Stream Chat’s input token handling. He implemented a targeted fix in Python to ensure accurate tracking of token usage during streaming chat sessions, which improved the correctness of the integration and enhanced test coverage. Guillaume updated unit tests to validate the new input token behavior, supporting a version bump to reflect these backend improvements. His work emphasized API integration and robust backend development, prioritizing correctness and release readiness over new features, and demonstrated careful attention to detail in production code quality.