Table of Contents
Quick Verdict
An e-commerce platform generating product imagery on demand needs its image API to deliver consistent throughput under load. SDXL serves 2.9 images per second at 678 ms median latency, using just 7 GB of VRAM. Flux.1 manages 2.3 at 1,496 ms median but produces visibly higher-quality outputs. On a dedicated GPU server, SDXL is the throughput champion while Flux.1 is the quality champion.
The 3.4x VRAM gap (7 GB versus 24 GB) is the structural constraint: SDXL leaves 17 GB free for other models or batching, while Flux.1 fully consumes a 24 GB GPU.
Full data below. More at the GPU comparisons hub.
Specs Comparison
SDXL uses traditional latent diffusion with a 3.5B UNet. Flux.1’s 12B rectified flow transformer represents a newer architectural approach that trades compute for quality.
| Specification | SDXL | Flux.1 |
|---|---|---|
| Parameters | 3.5B (UNet) | 12B |
| Architecture | Latent Diffusion | Rectified Flow Transformer |
| Context Length | 1024×1024 | 1024×1024 |
| VRAM (FP16) | 7 GB | 24 GB |
| VRAM (INT4) | N/A | N/A |
| Licence | CreativeML Open RAIL++-M | Apache 2.0 (schnell) |
Guides: SDXL VRAM requirements and Flux.1 VRAM requirements.
API Throughput Benchmark
Tested on an NVIDIA RTX 3090 at default 1024×1024 resolution. See our benchmark page.
| Model (INT4) | Requests/sec | p50 Latency (ms) | p99 Latency (ms) | VRAM Used |
|---|---|---|---|---|
| SDXL | 2.9 | 678 | 3249 | 7 GB |
| Flux.1 | 2.3 | 1496 | 2129 | 24 GB |
Interestingly, Flux.1 has a tighter p99 (2,129 ms versus 3,249 ms) despite higher median latency, suggesting more predictable generation times. SDXL’s wider p50-to-p99 spread indicates more latency variance under load. See our best GPU for LLM inference guide.
See also: SDXL vs Flux.1 for Cost-Optimised Batch Processing for a related comparison.
See also: SD 1.5 vs SDXL for API Serving (Throughput) for a related comparison.
Cost Analysis
SDXL’s 75% lower cost per 1K images reflects both its higher throughput and lower VRAM requirements.
| Cost Factor | SDXL | Flux.1 |
|---|---|---|
| GPU Required | RTX 3090 (24 GB) | RTX 3090 (24 GB) |
| VRAM Used | 7 GB | 24 GB |
| Images/min | 4.4 | 2.8 |
| Cost/1K Images | £1.6 | £2.81 |
See our cost calculator.
Recommendation
Choose SDXL for high-volume image APIs where throughput and cost per image drive business economics. Product imagery, thumbnail generation, and placeholder images all benefit from SDXL’s speed and efficiency.
Choose Flux.1 for APIs where image quality is the selling point — premium creative tools, marketing asset generation, or any endpoint where users directly evaluate visual fidelity.
Serve on dedicated GPU servers for consistent image generation performance.
Deploy the Winner
Run SDXL or Flux.1 on bare-metal GPU servers with full root access, no shared resources, and no token limits.
Browse GPU Servers
