Mathieu Orhan focused on improving reliability and shape stability in PyTorch-based machine learning workflows during April 2026. Working across the pytorch/tensordict and pytorch/rl repositories, he addressed two critical bugs by refining tensor operations and reward calculations. Using Python and PyTorch, Mathieu resolved an unravel_keys inconsistency to ensure compatibility with torch.compile, which reduced runtime errors and streamlined adoption of new compilation features. He also updated the LineariseRewards transform to preserve trailing dimensions in reward tensors, preventing unintended shape changes. His work demonstrated strong debugging and testing skills, contributing to more maintainable and robust data processing pipelines in these projects.