Loss Function Abstraction With Standard And Custom Objectives

Multi-backend deep learning API for JAX, TF, and PyTorch.

Unique: Keras 3's loss functions are backend-agnostic and automatically differentiated using the compiled backend's autodiff system, with support for both built-in losses (optimized implementations) and custom losses (user-defined Python functions), enabling flexible objective specification without backend-specific code.

vs others: More flexible than PyTorch's `torch.nn` loss functions because custom losses are first-class citizens and automatically integrated with the training loop, and simpler than TensorFlow's loss API which requires explicit reduction specification.