Flux vs SD model comparator
Choosing an image model is a trade-off between prompt fidelity, speed, ecosystem, licensing and hardware. Flux.1 leads on out-of-the-box quality and prompt-following; SDXL and SD 1.5 win on community fine-tunes, ControlNets and lightweight hardware. Tell this tool your use case and what you care about most, and it ranks the five options for you.
How the models differ
- SD 1.5 — old but unbeaten on ecosystem size. Thousands of LoRAs and ControlNets, runs on almost anything. Lower base fidelity and a relatively small 512×512 native resolution mean outputs can look soft compared with newer models.
- SDXL — the mature middle ground: strong quality, 1024×1024 native resolution, huge fine-tune library, runs comfortably on 8 GB VRAM. The refiner pipeline can add further detail.
- Flux.1 Schnell — distilled for 1–4 step speed, Apache-2.0 licensed (great for commercial drafts), slightly less detailed than Dev.
- Flux.1 Dev — best open-weight quality and prompt-following, but non-commercial licence and heavy on VRAM (comfortably runs at 16–24 GB).
- Flux.1 Pro — top quality, API-only, commercial-friendly, no local runs.
Side-by-side comparison table
| SD 1.5 | SDXL | Flux Schnell | Flux Dev | Flux Pro | |
|---|---|---|---|---|---|
| Native resolution | 512 px | 1024 px | 1024 px | 1024 px | 1024 px |
| Typical VRAM | 4–6 GB | 8–12 GB | 12–16 GB | 16–24 GB | API only |
| Steps (typical) | 20–50 | 20–40 | 1–4 | 20–50 | managed |
| Commercial use | Yes | Yes | Yes (Apache 2.0) | Non-commercial | Yes |
| LoRA / fine-tune | Thousands | Many | Growing | Growing | No |
| ControlNet | Extensive | Good | Limited | Limited | No |
| Prompt fidelity | Moderate | Good | Good | Excellent | Excellent |
Choosing by use case
Fast drafts and ideation. Flux Schnell’s 1–4 step generation is by far the fastest option for cycling through concepts. Its Apache 2.0 licence means you can use the output commercially. The trade-off is slightly less fine detail than Dev or Pro.
Polished commercial output. Flux Pro (API) or SDXL with a quality fine-tune. Pro gives the highest output quality with no local hardware requirement. SDXL is the best local option if you need full commercial rights with no API dependency.
Consistent characters or custom styles. SD 1.5 or SDXL, because both have mature LoRA and DreamBooth ecosystems. Thousands of publicly released fine-tunes cover specific art styles, character types, and photography aesthetics. Flux fine-tuning support is emerging but not yet as extensive.
Controlled composition (pose, depth, edge). SD 1.5 has the widest ControlNet support — OpenPose, depth, Canny, and dozens of other control types are well-tested. SDXL ControlNet support is solid. Flux ControlNet is more limited at the time of writing.
Text in images. Flux models handle text rendering in generated images significantly better than SD 1.5 or SDXL, which frequently distort or hallucinate words. If legible signage, labels, or UI mockups matter, Flux has a clear advantage.
Licensing — a quick summary
SD 1.5 uses the CreativeML Open RAIL-M licence, which is permissive for most uses. SDXL uses a similar licence. Flux Schnell is Apache 2.0 — one of the most permissive open-source licences available. Flux Dev is subject to a non-commercial use restriction. Flux Pro is commercial but requires API access through Black Forest Labs. Always verify the current licence directly from the model repository before shipping commercial work, as terms can change.
Tips
- Need ControlNet or a specific LoRA? Check the ecosystem first — that often forces SDXL or SD 1.5 regardless of base quality.
- Shipping commercial work? Avoid Flux Dev’s non-commercial licence; use Schnell, Pro, or SDXL.
- On a laptop GPU? SD 1.5 or a quantised SDXL will be far happier than Flux Dev.
- Text or hand accuracy? Flux models are notably better at rendering hands and text than earlier architectures — if either matters, prefer Flux.