At 16384, each GEMM saturates 97% of 132 SMs — no room for multi-stream parallelism. At 8192, GEMMs use ~50% SMs, allowing branch streams and aux parallelism to fill idle SMs. 2x more steps/epoch but each ~2x faster. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>