HobbyLM-Image — 1024px text-to-image DiT

The odd one out in the HobbyLM family: not a language model, but a 333M in-context flow-matching DiT that generates 1024×1024 images. It was built to see how good a text-to-image model you can train on a genuinely small budget — the whole thing came together for roughly $300 of Modal GPU time by working in a heavily compressed latent space instead of pixels.

It runs in the DC-AE f32c32 (SANA-1.1) latent (32× spatial compression → a 32×32×32 latent at 1024px) and is conditioned on CLIP-L text features, with classifier-free guidance.

Intended use

Text-to-image generation at 1024×1024. Strongest on single objects and cinematic scenes. A sibling 512px checkpoint additionally does instruction-based image editing.

How it works

CLIP-L(prompt) ─┐
                ├─►  DiT  ──(rectified-flow / CFG sampler, ~100 steps)──►  latent  ──►  DC-AE decode  ──►  1024² image
 Gaussian noise ─┘     (this repo)                                                       (frozen VAE)

The two frozen components are not included (download them from their own repos): mit-han-lab/dc-ae-f32c32-sana-1.1-diffusers (VAE) and openai/clip-vit-large-patch14 (text encoder). A full from-scratch CPU implementation of this pipeline (CLIP + DiT + DC-AE, in Rust) lives in hobby-rs.

Samples

1024×1024, generated by this model (CFG ≈ 5, ~100 steps):

Results

This is a hobby-scale generator, so the honest "benchmark" is the training curve and qualitative behaviour rather than FID / GenEval (which we did not compute):

Property	Value
Flow-matching loss (final)	0.76 (lowest of the model lineage — still decreasing)
Parameters	333M (DiT only)
Resolution	1024×1024 (32×32×32 latent)
VAE reconstruction	~26 dB PSNR @512px; sharper at 1024px (32×32 latent)

Qualitatively, the final checkpoint produces accurate objects and cinematic scenes. It is soft on people, hands, and multi-person scenes — the real small-model / latent-resolution ceiling. Loss was still dropping at the end of training, so the 333M DiT is not yet saturated.

Files

• model.safetensors — the DiT weights.
• config.json — DiT config, lat_std, and the VAE scaling_factor.

There is no GGUF build: image-generation DiTs have no standard GGUF runtime.

Limitations

• Hands and multi-person scenes are unreliable.
• Fine object crispness is capped by the 32× DC-AE latent; a less-compressed VAE would sharpen it at higher cost.
• Instruction-based editing is limited (the CLIP-L text encoder is a weak instruction follower); the real fix is a stronger conditioner, which is future work.

License

Apache-2.0.