### What does this PR do? Type of change: new feature (not yet user-reachable) **First of two PRs adding IQ1_M** at 1.75 bits per weight, just above IQ1_S. This one lands the **PyTorch codec**: encoder and decoder. It is deliberately **not registered**, so no quantizer dispatches to it and the `ggml` package does not export it. #2595 adds the CUDA encoder, registers the format and adds its recipe. With both, ModelOpt supports all five GGML IQ formats at one and two bits. On the mixed-precision checkpoint #2511 measured (`unsloth/Qwen3.8-27B-GGUF`), IQ1_M covers **25 tensors and 1.2 B parameters**. With all five formats we can read 89.0% of that file; the rest is k-quants and F32. ### What's distinctive about it **IQ1_M is the most irregular layout of the five.** There is no leading block scale field at all. The FP16 super-block scale is reassembled from the top nibble of each of four scale words: ```c scale.u16 = (sc[0] >> 12) | ((sc[1] >> 8) & 0x00f0) | ((sc[2] >> 4) & 0x0f00) | (sc[3] & 0xf000); ``` It is also finer grained than IQ1_S: a local scale per **two** groups rather than four, and a delta shift chosen **per group** rather than per sub-block. That is where its extra 0.1875 bits go. ### Shared with IQ1_S rather than copied IQ1_M searches exactly as IQ1_S does: the same 2048-entry grid, the same ±1/8 delta, every (shift, local scale) choice for every 8-value vector. It differs only in how it selects among those choices afterwards. So the search moves out of IQ1_S's encoder into `_search_shifted_grid`, which both call, and `iq1_m.py` keeps only its selection and packing. **IQ1_S's encoded bytes are unchanged**, checked by hashing its output before and after on a fixed input. ### A scale-anchor correction IQ1_M anchors its scale differently from IQ1_S: the ratio **rises with a block's peak-to-RMS** rather than being flat, and clamps higher. It uses `clamp(0.58 + 0.035 * peak_to_rms, 0.65, 0.95)` against IQ1_S's flat `0.61`. Measured over 15 Qwen3.8-27B MLP weights: | | flat 0.61 | correct anchor | | |---|---|---|---| | relative reconstruction MSE | 0.17372 | **0.17291** | **−0.47%** | It is consistent on every tensor, with no outliers. The anchor changes quality without touching layout, so neither round-trip nor conformance tests would catch it drifting. `test_scale_anchor_follows_peak_to_rms` now pins it, for all five formats; see Testing. ### Family parity Two surface asymmetries close here, so the five are uniform. `IQ1_S` now exposes `_predict_iq1_s_scales` like the other four, instead of computing its anchor inline. `IQ1_M` exposes `iq1_m_grid`, aliasing the IQ1_S table it shares. ### Testing **The decoder is validated against llama.cpp's own output, not just round-tripped:** ``` IQ1_M: 25 tensors, 4,730,880 blocks → 0 mismatched, max|diff| 0.0 ``` This mattered: **my first IQ1_M decoder had a real bug.** A `repeat_interleave` on the wrong axis produced `[h0,h1,h0,h1]` where llama.cpp needs `[h0,h0,h1,h1]`. A round-trip against our own encoder still passed, because the encoder made the matching mistake. Only comparison against bytes we did not produce caught it. Blocks from that checkpoint ship as conformance vectors, and mutation testing confirms they catch a mis-set scale nibble. The decoder unpacks every field in one vectorized pass, since fake quant decodes on every forward: 5.2 ms for a 5632×2048 weight (IQ1_S: 3.3). - `tests/unit/torch/quantization/test_ggml_backend.py`, `test_iq_formats.py`, `tests/unit/torch/export/test_convert_hf_config.py`, `tests/unit/recipe/test_presets.py`: **153 passed**, 15 of them IQ1_M codec cases, including the llama.cpp conformance check - `test_scale_anchor_follows_peak_to_rms` pins every format's scale anchor. It predicts scales for blocks whose peak-to-RMS is exactly 1, 4, 8 and 16, reaching both clamps and two points on each slope, and compares them against anchors written out in the test. Mutations each fail exactly the mutated format: reverting IQ1_M to IQ1_S's flat 0.61, moving either IQ1_M clamp, changing its taper by 0.001, moving an IQ2_S or IQ2_XS clamp, and changing IQ1_S's anchor to 0.62. - `tests/gpu/torch/quantization/test_iq_formats_cuda.py`, `test_iq1_s_cuda.py`, `test_iq2_xs_cuda.py`: **42 passed**. IQ1_S's CUDA-vs-PyTorch parity still holds after its encoder refactor. - IQ1_S and IQ1_M PyTorch encoder output and IQ1_M decoder output hash identically to the pre-split version of this PR. ### Before your PR is "*Ready for review*" - Is this change backward compatible?: ✅ - If you copied code from any other sources or added a new PIP dependency, did you follow guidance in `CONTRIBUTING.md`: ✅ IQ1_M adds no codebook; it reuses the IQ1_S table already carried in `codebooks.py`. The new conformance vectors come from `unsloth/Qwen3.8-27B-GGUF`, which is Apache-2.0 like its base model `Qwen/Qwen3.8-27B`; the vectors' docstring now records that. No new dependencies. - Did you write any new necessary tests?: ✅ - Did you update Changelog?: N/A. Nothing is user-reachable yet; #2595 carries the entry. - Did you get Claude approval on this PR?: ❌ Not yet run. ### Additional Information Merge order: #2511 (IQ2_XXS) → #2525 (format registry) → #2512 (IQ2_S codec) → #2565 (IQ2_S CUDA encoder and registration), all merged → **this** → #2595 (IQ1_M CUDA encoder and registration). 🤖 Generated with [Claude Code](https://claude.com/claude-code) <!-- This is an auto-generated comment: release notes by coderabbit.ai --> ## Summary by CodeRabbit * **New Features** * Added IQ1_M quantization and dequantization for compact, GGML-compatible blocks of 256 values. * Added access to the IQ1_M grid and configurable chunk sizes for processing data. * **Bug Fixes** * Improved IQ1_S scale prediction and grid-search organization while preserving its encoding behavior. * **Tests** * Added IQ1_M conformance data and included the format in shared IQ-format test coverage. <!-- end of auto-generated comment: release notes by coderabbit.ai --> --------- Signed-off-by: Chenjie Luo <chenjiel@nvidia.com> Co-authored-by: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
NVIDIA Model Optimizer (referred to as Model Optimizer, or ModelOpt) is a library comprising state-of-the-art model optimization techniques including quantization, pruning, Neural Architecture Search (NAS), distillation, speculative decoding and sparsity to accelerate models.
[Input] Model Optimizer currently supports inputs of a Hugging Face, PyTorch or ONNX model.
[Optimize] Model Optimizer provides Python APIs for users to easily compose the above model optimization techniques and export an optimized quantized checkpoint. Model Optimizer is also integrated with NVIDIA Megatron-Bridge, Megatron-LM and Hugging Face Accelerate for training required inference optimization techniques.
[Export for deployment] Seamlessly integrated within the NVIDIA AI software ecosystem, the quantized checkpoint generated from Model Optimizer is ready for deployment in downstream inference frameworks like SGLang, TensorRT-LLM, TensorRT, or vLLM. The unified Hugging Face export API now supports both transformers and diffusers models.
Latest News
- [2026/09/16] End-to-end W4A4 NVFP4 + QAD tutorial for Qwen3.6-35B-A3B: NVFP4 W4A4 PTQ plus quantization-aware distillation, reaching up to 1.30x vLLM throughput over BF16 and 3.1x smaller checkpoints while recovering the accuracy W4A4 costs.
- [2026/09/09] BLOG: Improving NVFP4 Accuracy with Local-Hessian Weight Scales
- [2026/08/24] BLOG: AutoQuantize: A Fast Automatic Mixed-Precision Assignment
- [2026/08/17] BLOG: Developing Nemotron 3.5 Lightning NVFP4 with QAD Using NVIDIA Model Optimizer: Learn how quantization-aware distillation recovers accuracy from aggressive NVFP4 quantization while reducing model size and increasing throughput.
- [2026/06/26] BLOG: Creating the NVIDIA Nemotron 3 Ultra NVFP4 Checkpoint with NVIDIA Model Optimizer: How we quantized Nemotron 3 Ultra (550B) to NVFP4 with Model Optimizer — up to 5.9× higher decode-heavy inference throughput than GLM-5.1 754B FP4 while matching BF16 accuracy. NVFP4 Checkpoint on Hugging Face.
- [2026/05/27] End-to-end Optimization tutorial for Nemotron-3-Nano-30B-A3B: Pruning + two-phase distillation + FP8 quantization achieving 2.6× vLLM throughput and 2.6× memory reduction.
- [2026/05/13] Puzzletron: A new algorithm for heterogeneous pruning & NAS of LLM and VLM models.
- [2026/04/15] Customer story: Domyn compresses Colosseum-355B → 260B using ModelOpt's Minitron pruning + distillation
- [2026/03/17] Customer story: Bielik.AI builds Bielik Minitron 7B (33% smaller, 50% faster, 90% quality retained) using ModelOpt's Minitron pruning + distillation
- [2026/03/11] Model Optimizer quantized Nemotron-3-Super checkpoints are available on Hugging Face for download: FP8, NVFP4. Learn more in the Nemotron 3 Super release blog. Check out how to quantize Nemotron 3 models for deployment acceleration here
- [2026/03/11] NeMo Megatron Bridge now supports Nemotron-3-Super quantization (PTQ and QAT) and export workflows using the Model Optimizer library. See the Quantization (PTQ and QAT) guide for FP8/NVFP4 quantization and HF export instructions.
- [2025/12/11] BLOG: Top 5 AI Model Optimization Techniques for Faster, Smarter Inference
- [2025/12/08] NVIDIA TensorRT Model Optimizer is now officially rebranded as NVIDIA Model Optimizer.
- [2025/10/07] BLOG: Pruning and Distilling LLMs Using NVIDIA Model Optimizer
- [2025/09/17] BLOG: An Introduction to Speculative Decoding for Reducing Latency in AI Inference
- [2025/09/11] BLOG: How Quantization Aware Training Enables Low-Precision Accuracy Recovery
- [2025/08/29] BLOG: Fine-Tuning gpt-oss for Accuracy and Performance with Quantization Aware Training
- [2025/08/01] BLOG: Optimizing LLMs for Performance and Accuracy with Post-Training Quantization
- [2025/06/24] BLOG: Introducing NVFP4 for Efficient and Accurate Low-Precision Inference
- [2025/05/14] NVIDIA TensorRT Unlocks FP4 Image Generation for NVIDIA Blackwell GeForce RTX 50 Series GPUs
- [2025/04/21] Adobe optimized deployment using Model-Optimizer + TensorRT leading to a 60% reduction in diffusion latency, a 40% reduction in total cost of ownership
- [2025/04/05] NVIDIA Accelerates Inference on Meta Llama 4 Scout and Maverick. Check out how to quantize Llama4 for deployment acceleration here
- [2025/03/18] World's Fastest DeepSeek-R1 Inference with Blackwell FP4 & Increasing Image Generation Efficiency on Blackwell
- [2025/02/25] Model Optimizer quantized NVFP4 models available on Hugging Face for download: DeepSeek-R1-FP4, Llama-3.3-70B-Instruct-FP4, Llama-3.1-405B-Instruct-FP4
- [2025/01/28] Model Optimizer has added support for NVFP4. Check out an example of NVFP4 PTQ here.
- [2025/01/28] Model Optimizer is now open source!
Previous News
- [2024/10/23] Model Optimizer quantized FP8 Llama-3.1 Instruct models available on Hugging Face for download: 8B, 70B, 405B.
- [2024/09/10] Post-Training Quantization of LLMs with NVIDIA NeMo and Model Optimizer.
- [2024/08/28] Boosting Llama 3.1 405B Performance up to 44% with Model Optimizer on NVIDIA H200 GPUs
- [2024/08/28] Up to 1.9X Higher Llama 3.1 Performance with Medusa
- [2024/08/15] New features in recent releases: Cache Diffusion, QLoRA workflow with NVIDIA NeMo, and more. Check out our blog for details.
- [2024/06/03] Model Optimizer now has an experimental feature to deploy to vLLM as part of our effort to support popular deployment frameworks. Check out the workflow here
- [2024/05/08] Announcement: Model Optimizer Now Formally Available to Further Accelerate GenAI Inference Performance
- [2024/03/27] Model Optimizer supercharges TensorRT-LLM to set MLPerf LLM inference records
- [2024/03/18] GTC Session: Optimize Generative AI Inference with Quantization in TensorRT-LLM and TensorRT
- [2024/03/07] Model Optimizer's 8-bit Post-Training Quantization enables TensorRT to accelerate Stable Diffusion to nearly 2x faster
- [2024/02/01] Speed up inference with Model Optimizer quantization techniques in TRT-LLM
Install
To install stable release packages for Model Optimizer with pip from PyPI:
pip install -U nvidia-modelopt[all]
Model Optimizer will download and install additional third-party open source software projects. Review the license terms of these open source projects before use.
To install from source in editable mode with all development dependencies or to use the latest features, run:
# Clone the Model Optimizer repository
git clone git@github.com:NVIDIA/Model-Optimizer.git
cd Model-Optimizer
pip install -e .[dev]
You can also directly use NVIDIA container images, which have Model Optimizer pre-installed:
nvcr.io/nvidia/pytorch:<version>-py3nvcr.io/nvidia/nemo:<version>nvcr.io/nvidia/tensorrt-llm/release:<version>
Before pulling and using the container images, please review their respective license terms. Make sure to upgrade Model Optimizer to the latest version as described above. Visit our installation guide for more fine-grained control on installed dependencies or for alternative docker images and environment variables to setup.
Techniques
| Technique | Description | Getting started | Examples |
|---|---|---|---|
| Post Training Quantization | Compress model size by 2x-4x, speeding up inference while preserving model quality! | [Start here] | [HF LLMs / VLMs] [Megatron-Bridge LLMs / VLMs] [Diffusers] [ONNX] [Windows] |
| Quantization Aware Training / Distillation | Refine accuracy of quantized models even further with a few training steps! | [Start here] | [Hugging Face] [Megatron-Bridge] |
| Pruning | Reduce your model parameters or memory footprint and accelerate inference by removing unnecessary weights! | [Start here] | [General] [Megatron-Bridge] |
| Distillation | Reduce deployment model size by teaching small models to behave like larger models! | [Start here] | [Hugging Face] [Megatron-Bridge] [Megatron-LM] |
| Speculative Decoding | Train draft modules to predict extra tokens during inference! | [Start here] | [Hugging Face] [Megatron-LM] |
| Sparsity | Efficiently compress your model by storing only its non-zero parameter values and their locations | [Start here] | [Hugging Face] |
Pre-Quantized Checkpoints
- Ready-to-deploy checkpoints [🤗 Hugging Face - Nvidia Model Optimizer Collection]
- Deployable on TensorRT-LLM, vLLM and SGLang
- More models coming soon!
Resources
Model Support Matrix
| Model Type | Support Matrix |
|---|---|
| LLM / VLM Quantization | View Support Matrix |
| Diffusers Quantization | View Support Matrix |
| ONNX Quantization | View Support Matrix |
| Windows Quantization | View Support Matrix |
| Quantization Aware Training | View Support Matrix |
| Pruning | View Support Matrix |
| Distillation | View Support Matrix |
| Speculative Decoding | View Support Matrix |
Deprecation Policy
Model Optimizer follows a structured approach to managing deprecated features:
- Communication: Deprecation notices are documented in the Changelog. Deprecated items include source code statements indicating deprecation timing, with runtime warnings issued upon use.
- Migration Period: Since Model Optimizer is still pre-1.0, we provide a 1-release (~1-month) migration period after deprecation. During this window, deprecated features continue functioning while issuing warnings.
- Scope: The policy addresses both complete deprecations (entire APIs removed) and partial ones (specific parameters removed while methods remain).
- Removal: Following the migration period, deprecated elements are removed in alignment with semantic versioning standards, potentially including breaking changes in minor version updates while Model Optimizer remains in 0.x.
Citation
If you use NVIDIA Model Optimizer in your research, please cite it as follows:
@misc{nvidia-modelopt,
author = {{NVIDIA Corporation}},
title = {{NVIDIA Model Optimizer}},
howpublished = {\url{https://github.com/NVIDIA/Model-Optimizer}},
year = {2024--2026},
note = {GitHub repository}
}
Contributing
Model Optimizer is now open source! We welcome any feedback, feature requests and PRs. Please read our Contributing guidelines for details on how to contribute to this project.
AI Agents
ModelOpt's agent skills can be installed from this repository and used in any workspace.
Claude Code
claude plugin marketplace add https://github.com/NVIDIA/Model-Optimizer.git
claude plugin install modelopt@modelopt
Codex
codex plugin marketplace add https://github.com/NVIDIA/Model-Optimizer.git
Then open /plugins, select the modelopt marketplace, and install modelopt.
Contributors can also use the skills directly from a checkout. See the
agent tooling notes.
Top Contributors
Happy optimizing!
