As a Senior Research Engineer at Fitbit, you'll be responsible for designing, implementing, and optimizing machine learning models for various health and fitness applications. You will collaborate with cross-functional teams to develop and launch new features, working with technologies such as TensorFlow, PyTorch, or Jax. The role involves writing and testing code, contributing to documentation, debugging system issues, and managing the machine learning project lifecycle. You will leverage your expertise in model pretraining, fine-tuning, evaluation, and optimization, contributing to Fitbit's mission of making health more accessible.