bonsai-image-ternary-4B-gemlite-2bit

Ternary weight (1.58-bit) text-to-image diffusion transformer deployment for NVIDIA GPUs

1.21 GB transformer | 6.4× smaller than FP16 | 4.5 s / 1024² on RTX 3080 | 2.8 s / 1024² on A100 | runs natively on Linux and Windows

Highlights

• 1.21 GB diffusion transformer, down from 7.75 GB for the FP16 FLUX.2 Klein 4B transformer
• Ternary {-1, 0, +1} transformer weights with FP16 group-wise scaling in the matrix-heavy transformer layers (Q/K/V projections, output projections, MLP weights)
• Quality-oriented Bonsai Image variant: the additional zero state improves visual quality and prompt fidelity while keeping the transformer compact
• 4.55 GB CUDA deployment payload including the 4-bit text encoder and FP16 VAE — text encoder is offloaded after prompt encode, so the denoising loop only keeps the compact transformer and VAE resident
• 4-step FlowMatch-Euler sampler with guidance = 1.0 and shift = 3.0 — no CFG, no negative prompts needed
• Gemlite low-bit GEMM path for NVIDIA GPUs, with HQQ used for the compressed text encoder
• Runs on Linux and Windows natively through the same CUDA / Gemlite deployment stack
• Cross-platform companion: also available as MLX 2-bit for Apple Silicon

Resources

• White Paper — full benchmarks, kernels, and memory analysis
• Demo repo — one-command setup for Mac / Linux / Windows
• Discord — community + support
• Kernels: gemlite (fused low-bit GEMM) · HQQ (low-bit quantization runtime) · triton-windows (Windows path)

Model Overview

Ternary Weight Representation: 1.58-bit g128

Each ternary weight takes a value from {−1, 0, +1} with one shared FP16 scale per group of 128 weights:

w_i = scale_g * t_i,    t_i in {−1, 0, +1}

Ternary values carry log₂(3) ≈ 1.585 bits of information per weight. With one FP16 scale per group of 128, the effective storage is:

b_eff ≈ log2(3) + 16/128 ≈ 1.585 + 0.125 ≈ 1.71 bits/weight

This gives an idealized 9.4× reduction relative to FP16 for the ternary transformer layers. A small set of precision-sensitive supporting tensors remains in FP16, so the final Ternary Bonsai Image 4B diffusion transformer is 1.21 GB, a 6.4x reduction from the 7.75 GB FP16 FLUX.2 Klein 4B transformer.

The ternary representation is applied to the matrix-heavy transformer layers, including Q / K / V projections, output projections, MLP linears, and the double-stream add-K / Q / V linears. Supporting tensors (less than 5% of the total parameters) such as modulation streams, embedders, output norm, and output projection remain FP16 for image quality and stability.

The CUDA deployment uses a Gemlite INT2 packed format. Ternary values are stored in 2-bit slots, with the fourth code unused. The model-level Bonsai representation is 1.21 GB; the deployed CUDA pack is 1.54 GB on disk due to runtime packing and alignment overhead in the current Gemlite path.

Memory

CUDA deployment:

At runtime, the text encoder is offloaded after prompt encoding. During denoising, the repeated image-generation loop is dominated by the compact ternary diffusion transformer and active image-generation components rather than the full payload.

Peak HBM at 1024² on RTX 3080 is ~6.8 GiB end-to-end (transformer + VAE + activation memory).

Best Practices

• Sampler: FlowMatchEuler-discrete with 4 steps, guidance = 1.0, shift = 3.0. The model is designed for 4 steps; running more steps does not improve quality significantly and can introduce artifacts.
• Resolution: native 1024² is the design target. 512² works for quick previews.
• Aspect ratios: multiples of 32 are supported, including 832x1248 and 1248x832.
• Prompting: natural-language prompts. Negative prompts are not required.
• Runtime memory: the text encoder is offloaded after prompt encoding, so the denoising loop is memory-light.

Quickstart

Bonsai Studio (Linux / Windows)

The simplest path is the Bonsai Image Demo repo, which sets up the full Bonsai Studio (FastAPI backend + Next.js frontend) and selects gemlite automatically on Linux / Windows:

git clone https://github.com/PrismML-Eng/Bonsai-Image-Demo.git
cd Bonsai-Image-Demo
./setup.sh
./scripts/download_model.sh           # ternary is the default
./scripts/serve.sh

On Windows (PowerShell):

Set-ExecutionPolicy -Scope CurrentUser RemoteSigned   # one-time
.\setup.ps1
.\scripts\download_model.ps1
.\scripts\serve.ps1

Python API (backend_gpu)

For inference without the studio frontend:

from backend_gpu.server import build_pipeline

pipe = build_pipeline(model_id="prism-ml/bonsai-image-ternary-4B-gemlite-2bit")
image = pipe(
    prompt="A bonsai tree in a quiet ceramic studio, soft morning light",
    num_inference_steps=4,
    guidance_scale=1.0,
    height=1024,
    width=1024,
).images[0]
image.save("bonsai.png")

Throughput (CUDA / gemlite)

Warmed wall-clock per image, 4 denoising steps, guidance = 1.0, matched prompts and sampler settings.

The sub-2-bit pack keeps generation viable on commodity GPUs at 1024². The RTX 3080 10 GB reaches 4.5 s/image, while the 6 GB laptop RTX 3060 is the memory-constrained tail.

Benchmarks

Evaluated with matched generation settings across the comparison set on H100. GenEval uses the official 512x512 protocol. For HPSv3 and DPG-Bench, larger-backbone rows are evaluated at 1024x1024, while smaller-backbone rows are evaluated at their native 512x512 setting. Higher is better for all three benchmarks.

The benchmark results show the intended quality-footprint trade-off. Ternary Bonsai Image 4B is the quality-oriented variant: at 1.21 GB, it sits very close to FLUX.2 Klein 4B across GenEval, HPSv3, and DPG-Bench while reducing the diffusion transformer footprint by 6.4x. The binary companion is the footprint-oriented variant, reducing the diffusion transformer below 1 GB while still delivering strong benchmark results.

Together, the Bonsai Image variants move the quality-footprint frontier: they bring modern diffusion-transformer behavior into a memory range previously occupied by much smaller, lower-capability models.

Use Cases

• Local creative tooling: image generation directly on CUDA-equipped workstations and consumer GPUs
• Private generation: prompts and generated assets can remain in local or controlled environments
• Rapid iteration: lower local latency and no remote queue for iterative creative workflows
• Commodity-GPU serving: lower transformer footprint and reduced memory pressure for serving on NVIDIA GPUs
• Windows and Linux deployment: native paths through the same Gemlite deployment stack
• Enterprise and controlled inference: local or private environments for data residency and compliance-sensitive workflows

Limitations

• Ternary Bonsai Image 4B is not bit-identical to the FP16 FLUX.2 Klein 4B model; it is a compact ternary-weight deployment designed to deliver similar practical behavior at much smaller size.
• Image-generation quality remains prompt- and workflow-dependent. Small text, fine details, object counts, and strict compositional constraints should be evaluated for the target use case.
• Current commodity inference stacks do not yet expose fully native ternary execution as a standard hardware path. This release uses practical Gemlite low-bit GEMM kernels on CUDA.
• After the diffusion transformer is made compact, other components such as the VAE can become more visible memory bottlenecks. The runtime mitigates this with text-encoder offload and tiled VAE decoding.

Citation

@techreport{bonsaiimage4b,
    title   = {Bonsai Image 4B: Low-Bit Diffusion on Apple Silicon and Consumer GPUs},
    author  = {Prism ML},
    year    = {2026},
    month   = {May},
    url     = {https://prismml.com}
}

Contact

For questions, feedback, or collaboration inquiries: contact@prismml.com