PyTorch 2.15 Makes a Rewritten NCCL Backend the Default; Release Notes Say Groups Create Communicators Eagerly and Allocate GPU Memory Even if Unused
PyTorch 2.15.0 (October 28, 2026) makes a rewritten NCCL backend the default; its notes list eager communicators that allocate GPU memory and say nccl-legacy will be removed in the next release.