SD 3.5 Large Complete Guide: Stability AI's Best Model 2025

Stable Diffusion 3.5 Large represents Stability AI's most capable open model—delivering exceptional quality across photorealism, illustration, and abstract styles with improved text rendering and prompt following.

Quick Answer: SD 3.5 Large is an 8 billion parameter model offering the highest fidelity in the SD 3.5 family. It requires 12GB+ VRAM, works best with natural language prompts, and excels at text rendering. Available on ComfyUI with specific node requirements.

What Makes SD 3.5 Large Special?

SD 3.5 Large introduces several architectural improvements:

MMDiT Architecture: Multimodal Diffusion Transformer handles both image and text modalities more effectively than previous U-Net architectures.

Triple Text Encoders: Uses CLIP ViT-L, CLIP ViT-bigG, and T5-XXL for superior prompt understanding.

Improved Text Rendering: Finally generates readable text in images—a longtime weakness of diffusion models.

Style Versatility: Handles photorealism, digital art, anime, and abstract styles without fine-tuning.

Installing SD 3.5 in ComfyUI

Step 1: Download Required Files

From HuggingFace (requires acceptance of license):

• sd3.5_large.safetensors → models/checkpoints/
• clip_l.safetensors → models/clip/
• clip_g.safetensors → models/clip/
• t5xxl_fp16.safetensors → models/clip/ (or fp8 for lower VRAM)

Step 2: Install Required Nodes

Ensure you have nodes supporting SD3:

# Update ComfyUI to latest
cd ComfyUI
git pull

Step 3: Configure Memory

For 12GB cards, use fp8 T5 encoder:

t5xxl_fp8_e4m3fn.safetensors

For 24GB cards, use full fp16 T5 for best quality.

Optimal Settings for SD 3.5 Large

Resolution:

• Default: 1024x1024
• Supported: 512-2048 (multiples of 64)
• Best results: 1024x1024 or 1536x1024

Sampler Settings:

• Sampler: DPM++ 2M or Euler
• Scheduler: Simple or Karras
• Steps: 28-40 for quality, 20-25 for speed
• CFG Scale: 4.0-7.0 (lower than SDXL)

Key Difference: SD 3.5 responds better to lower CFG values. Start at 4.5 and adjust.

Prompting for SD 3.5

SD 3.5 responds better to natural language than keyword lists:

SDXL Style (Less Effective):

beautiful woman, photorealistic, 8k, detailed, studio lighting

SD 3.5 Style (More Effective):

A professional photograph of a young woman in a modern studio.
She has natural makeup and is lit by soft diffused lighting from
the left. The background is a gradient from dark grey to light.
Shot on a Canon EOS R5 with an 85mm lens at f/1.8.

Write prompts like descriptions rather than tag lists.

Text in Images

SD 3.5's text rendering is vastly improved:

A vintage coffee shop sign that reads "MORNING BREW" in
art deco lettering. The sign is made of aged brass with
warm lighting from below. Slight patina on the letters.

Include the exact text you want in quotes within your prompt.

Comparing SD 3.5 Variants

SD 3.5 vs SDXL vs Flux

SD 3.5 Large Advantages:

• Best text rendering
• Natural language prompting
• Style versatility without LoRAs
• Open weights (with license)

SDXL Advantages:

• Larger ecosystem of LoRAs/models
• More community resources
• Runs on 8GB VRAM
• More predictable output

Flux Advantages:

• Highest prompt adherence
• Best for specific compositions
• Excellent character consistency
• Different aesthetic (some prefer it)

Choose based on your specific needs. SD 3.5 Large is best for quality-focused work with text requirements.

Working with ControlNet

SD 3.5 has growing ControlNet support:

Available:

• Canny edge detection
• Depth guidance
• Pose control (experimental)

Usage: ControlNet for SD 3.5 requires specific models trained for the architecture. SDXL ControlNets won't work.

NVIDIA Optimizations

Stability AI partnered with NVIDIA for TensorRT optimizations:

Benefits:

• Faster inference
• Reduced VRAM usage
• FP8 support for 12GB cards

Setup: Available through Stability AI's optimized deployment packages or Azure AI Foundry.

Common Issues and Solutions

Issue: Oversaturated colors Solution: Lower CFG to 4.0-5.0

Issue: Text not rendering correctly Solution: Put exact text in quotes, be specific about font style

Issue: Out of VRAM Solution: Use fp8 T5 encoder, enable attention slicing

Issue: Generations look flat Solution: Add lighting descriptions to prompts, increase steps

Issue: Inconsistent style Solution: Be more descriptive in prompts, SD 3.5 responds to detail

Advanced Techniques

Multi-Pass Generation

1. Generate at 1024x1024 base resolution
2. Use SD 3.5 img2img to upscale to 2048
3. Final pass at low denoising for refinement

Style Mixing

SD 3.5 handles style mixing through prompting:

A portrait in the style of both classical oil painting and
modern digital art. Realistic proportions with painterly
brush strokes visible in the background.

Negative Prompts

SD 3.5 responds differently to negatives than SDXL:

• Keep negatives minimal
• Focus on specific artifacts to avoid
• Don't overload with quality terms

Frequently Asked Questions

Is SD 3.5 better than SDXL?

For quality and text rendering, yes. For ecosystem and VRAM requirements, SDXL may be more practical.

Can I use SDXL LoRAs with SD 3.5?

No, the architecture is different. SD 3.5 requires its own LoRAs.

What's the commercial license?

SD 3.5 has a Stability AI Community License. Check current terms for commercial use requirements.

Why are my results different from others?

Text encoders significantly impact output. Ensure you have all three CLIPs and the correct T5 variant.

Should I upgrade from SDXL?

If you need text rendering or prefer natural language prompting, yes. If you rely on SDXL LoRAs, maintain both.

Conclusion

SD 3.5 Large represents Stability AI's current best—superior prompt following, excellent text rendering, and remarkable versatility across styles. The trade-off is higher VRAM requirements and a less developed ecosystem compared to SDXL.

For quality-focused work, especially anything requiring text in images, SD 3.5 Large is the clear choice in the open-weights space. Learn its preference for natural language prompts and lower CFG values, and you'll achieve results that rival proprietary models.