Evaluate SageAttention3 as FlexAttention alternative for Blackwell #8
Description
Context
SageAttention3 has explicit Blackwell variant. Claims 2-5x speedup over FlashAttention with quantized attention (FP8/INT8).
Action Items
- Check sliding window + GQA support
- Install and benchmark on RTX 5090
- Compare val_bpb, tok/sec, VRAM vs FlexAttention