The backward branch parallelism allocated 4 × 32MB = 128MB for per-branch cuBLAS workspaces, pushing H100 VRAM over 80GB → OOM. Forward and backward are in the same child graph (sequential) — workspaces never conflict. Now backward receives forward's branch_workspace_ptrs as a parameter. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>