Flux 1.1 Pro Ultra vs Stable Diffusion 3.5: which open-ish model wins?
Flux 1.1 Pro Ultra is the higher-fidelity, prompt-adherence king but partly closed; SD 3.5 Large is genuinely open and the ComfyUI ecosystem winner. Pick Flux for quality, SD for control.
At a glance
| Dimension | Flux 1.1 Pro Ultra | Stable Diffusion 3.5 Large |
|---|---|---|
| Output quality (default) | State of the artWIN | Strong but a notch below |
| Prompt adherence | ExcellentWIN | Very good |
| Text in images | ExcellentWIN | Decent, lags Flux |
| Open weights | Only Flux 1 dev (older) | Yes — SD 3.5 Large fully openWIN |
| ControlNet / IP-Adapter ecosystem | Newer, fewer extensions | Largest in the industryWIN |
| Fine-tuning / LoRA | Supported on dev | Mature ecosystemWIN |
| Price (API) | ~$0.04/image (Pro Ultra) | Open weights — compute onlyWIN |
| Speed | 5-15 s on Pro UltraWIN | 12-30 s on a 24 GB GPU |
Verdict
If you need the absolute best one-shot quality on a brief, Flux 1.1 Pro Ultra wins; the gap on prompt adherence and text rendering is real. If you need to fine-tune on a brand, deploy on your own infra, or run ControlNet + IP-Adapter pipelines, Stable Diffusion 3.5 Large is still the platform — the ComfyUI ecosystem around it is years ahead of anything Flux has.
When to pick which
Pick Flux 1.1 Pro Ultra
Top-quality hero shots, ads, on-image typography, fastest path to a clean result.
Pick Stable Diffusion 3.5 Large
Self-hosting, custom LoRA on a character or brand, ControlNet workflows, infinite iteration.
FAQ
Is Flux better than Stable Diffusion 3.5?
On default output quality and prompt adherence, yes. On ecosystem, customisation, and self-hosting, Stable Diffusion 3.5 Large is still ahead.
Can I run Flux locally?
Yes — Flux 1 dev (older, smaller) runs on a 24 GB GPU with quantization. Flux 1.1 Pro Ultra is API-only.
Which is cheaper for high volume?
Stable Diffusion 3.5 Large on your own hardware is cheaper at scale; below ~5,000 images/month Flux 1.1 Pro Ultra wins on total cost.
Last updated: 2026-06-01.