Zhipeng Han refactored the HuggingFacePreTrainedBuilder within the apple/axlearn repository, focusing on improving maintainability and testability of the HuggingFace integration. By modularizing this component into its own Python module, Zhipeng enabled clearer separation of concerns and streamlined future enhancements. The approach emphasized code organization, reduced coupling, and facilitated easier onboarding for new contributors. Throughout the process, Zhipeng applied Python programming, module design, and unit testing skills, ensuring the refactor supported safer workflows and lower regression risk. The work demonstrated thoughtful engineering depth, prioritizing long-term stability and maintainability over immediate feature expansion or bug fixes during the development period.