P-JiT (Pyramid-JiT)

Code: github.com/Linum-AI/pyramid-jit
Blog post: Pyramid-JiT: Low-Res Drafts, High-Res Images

⚠️ Research checkpoint

This is an experimental research artifact, not a production model. P-JiT was trained for 138M samples and has not been post-trained. It is a research preview on the road to our v3 model. We're releasing it to share our preliminary findings with the broader field and to encourage others to explore efficient training methods like ours. Expect rough edges.

P-JiT reaches Linum v2's FD-DINOv2 on 11.3x fewer training samples and trains in 4.3x fewer GPU-hours, at 4x the pixels. Both figures are from the blog post, which has the full write-up.

P-JiT is a 2.2B-parameter pixel-space text-to-image diffusion transformer from Linum: a single decoder-only DiT that reads the noisy image as 32x32-pixel patches (256 tokens at 512x512) together with the caption and predicts the clean image directly, with no VAE. During training, extra readout heads predicted the image at 128x128 (after block 10) and 256x256 (after block 16) on the way to the final 512x512 head. Captions are encoded with Qwen3.5-4B (hidden layers 7/15/27 concatenated).

Code, sampler, and the reference training loss: github.com/Linum-AI/pyramid-jit.

Samples

512x512 samples from the blog post's appendix.

Files

Usage

git clone https://github.com/Linum-AI/pyramid-jit && cd pyramid-jit && pip install -e .
PROMPT="A close-up portrait of a young white woman with vibrant, fiery red hair cascading over \
her shoulders in soft waves, framed from the shoulders up and centered against a softly blurred \
warm-toned background. Her fair, lightly freckled complexion sets off piercing green eyes and a \
subtle, closed-lipped smile. Soft natural light enters from the left of the frame, highlighting \
the texture of her hair and the curve of her cheek while leaving the right side in gentle shadow. \
A shallow depth of field renders the background into smooth, neutral bokeh. Lights dangle out of \
focus on the left side of the frame."
python generate.py --weights Linum-AI/pyramid-jit --qwen_model_path Qwen/Qwen3.5-4B \
    --prompt "$PROMPT" --seeds 42

from pyramid_jit import PyramidJiT, QwenTextEncoder, SamplerConfig, generate

model = PyramidJiT.from_pretrained("Linum-AI/pyramid-jit")    # downloads from the Hub
text_encoder = QwenTextEncoder("Qwen/Qwen3.5-4B")
images = generate(model=model, text_encoder=text_encoder, prompt=prompt, seeds=[42],
                  sampler=SamplerConfig())

This generates the top-left sample above. The model was trained on dense captions (around 80 words); rewrite short prompts into a detailed description first.

Sampling: 50 Euler steps, adaptive projected guidance at scale 15, initial noise scale 2. The initial noise is drawn exactly as torch.randn draws it on an H100 SXM, the GPU the model was trained on, so a seed gives the same image on any NVIDIA GPU (see the code repository's README).

Provenance

Weights are the EMA (half-life 3,907 steps, from step 977) after 134,766 steps at batch size 1,024: 138M image samples, with logit-normal timesteps (0.8, 0.8) for the first 50M samples and (-0.2, 1.0) after.

The two readout heads (2.85M parameters) and the 145M-parameter PixelREPA masked transformer adapter (the representation-alignment loss's projection head) are training-only and not included; reference implementations are in the code repository's loss.py.

Authorship

This model card, and the code repository it points to, were written by Claude (Anthropic's Opus 5.5 model, running in Claude Code) at Linum's request: it extracted the model, inference code and training loss from Linum's internal experiment repository, exported these weights, and verified that they reproduce the internal sample images pixel for pixel. The model, its training, and the review of this release are Linum's.

License

Apache-2.0. Copyright 2026 Linum Inc.