ULT7RAFLUX

If you're going to try FLUXNATION, this is the node you actually want. ULT7RAFLUX is the pack's master node: it combines everything the other three do - the spike toggle from FLUXSPIKEY, the three tuning dials from FLUXATTENHUT - into a single pass-through you drop between your checkpoint loader and your KSampler. The other nodes are there so you can split the controls across a graph; this one is there so you don't have to.

FLUXNATION itself is a fused FP8 CUDA kernel for FLUX.1 that replaces ComfyUI's SingleStreamBlock forward pass with one torch.ops call, then layers a block-sparse "spike" attention pass and step caching on top to cut generation time on RTX 40-series cards. The kernel patches itself in at ComfyUI startup and runs whether or not any node is in the graph - so every node in this pack is really a control panel, and this one is the full panel. Feed it a MODEL, set your five inputs, and the same MODEL passes straight through. The printout in the console - [ULT7RAFLUX] FP8 fused kernel | spike=ON | cache=ON | switch=50% cap=45% tau=0.05 - is your confirmation that the settings actually landed.

The inputs, for a beginner who just wants it to work:

• spike (default true) - master enable for block-sparse attention. On, attention engages after switch_pct of the denoise; off, you're back to dense attention on the fused kernel.
• step_cache (default true) - alternates between computing spike attention and replaying the cached result, so every other spike step costs nothing. Keep it on; it's half the speed win.
• switch_pct (default 0.50) - when spike activates, as a fraction of steps. 0.50 = step 10 of 20. Early steps build structure and stay dense; this sets where the cheap phase begins.
• cap_pct (default 0.45) - the fraction of attention blocks kept once spike is active. Top 45% by dot-product score get computed, the rest are skipped. This is your speed/quality lever.
• tau (default 0.05) - block scoring threshold; lower keeps more blocks. The fine-grained companion to cap_pct.

The defaults are a sane starting point - the README's 4090 benchmark (20 steps, 1024×1024, ~9.3s vs ~13–14s stock) runs with exactly these. My honest advice: try it at defaults first, compare output to stock with the same seed, and only then start turning cap_pct down. If you turn the knobs blind you can't tell whether the softness you see is the spike path or your sampler.

Install is the pack install, which is the fiddly part and the same for every node in the pack. This is not a clean one-command thing. The README's route is:

git clone https://github.com/ULT7RA/cuda-kernels.git
# copy FLUXNATION/custom_nodes/FLUXNATION/ -> ComfyUI/custom_nodes/FLUXNATION/
cd FLUXNATION
build_ext.bat

The build needs Visual Studio 2022, CUDA Toolkit 12.x, and Python 3.10. setup_ext.py hardcodes -arch=sm_89 - this is a 4090 kernel; other Ampere/Ada cards "may work but untested," and you'll be editing the build script to make them build at all. It also expects CUTLASS headers in cutlass/include that aren't shipped in the repo, so be ready to supply them (grab NVIDIA/cutlass and point the include path at it). No requirements.txt; the node uses the torch and Triton already in your ComfyUI environment. Launch with the env vars from run_nvidia_gpu_spike.bat (FLUX_SPIKE=1 FLUX_SPIKE_SWITCH=0.50 FLUX_SPIKE_CAP=0.45 FLUX_SPIKE_TAU=0.05 FLUX_SPIKE_CACHE=1) - those set the startup defaults, and this node overrides them live without a restart.

Two gotchas to keep in mind. First, if the build failed or the extension never loaded, this node still passes the model through fine - it just prints DISABLED - extension not found and you get stock ComfyUI speed with no error. Check the console for the "ACTIVE" line or you'll think you're faster when you aren't. Second, the pack's own README is blunt: "No fallbacks. If it breaks, it crashes - no silent quality degradation." That's the design philosophy, and it's a feature for benchmarking but a liability for trusting it blind. The pack is new, single-author, and the r/StableDiffusion announcement (April 2026) was met with open skepticism - so treat ULT7RAFLUX as a promising experiment you verify, not a set-and-forget speed knob. Verify quality at your settings, keep the seed fixed, and you can decide for yourself whether the 30%+ claim holds on your card.