Metric Computation And Monitoring During Training

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

Unique: Keras 3's metrics use a stateful accumulation pattern where each `keras.metrics.Metric` object maintains internal state (e.g., running sum and count for averaging) across batches, enabling memory-efficient metric computation without storing all predictions, and supporting distributed training via state synchronization.

vs others: More memory-efficient than PyTorch's approach of storing all predictions and computing metrics post-hoc, and more flexible than TensorFlow's built-in metrics because custom metrics can override any part of the computation pipeline.