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yueshen2016andClaude Opus 5
fc4c40fcbe
### What does this PR do? Type of change: Bug fix `TensorQuantizer.export_amax()` early-returns `self.amax` unsanitized for dynamic-block quantizers, while the static path immediately below it has always substituted `maxbound` for zero/NaN entries. The `nvfp4` numerics unit sets `type: dynamic`, so a recipe that applies it to an *activation* quantizer — e.g. `general/ptq/nvfp4_mlp_only-kv_fp8_cast`, which targets `*mlp*input_quantizer` — feeds a raw `0.0` into `NVFP4QTensor.get_activation_scaling_factor`, whose assert aborts the entire export: ``` AssertionError: Failed to export module 'model.language_model.layers.37.mlp.gate_proj' (type=QuantLinear): activation scaling factor 0.0 not positive. ``` Calibration leaves `amax` at 0 whenever a layer — or an unrouted MoE expert — saw only zeros, so one dead layer costs the whole run at the final export step. This factors the substitution into `_sanitize_export_amax()` and calls it from both branches. Two details beyond de-duplication: - **Branch-free, so it survives a meta `amax`.** `torch.where` + `nan_to_num` both have meta kernels; `bool()` on a meta tensor raises. The layerwise and streaming export flows carry meta `amax` — `validate_attr` short-circuits on `is_meta` for exactly that reason — so only the warning is gated on a materialized tensor. - **No longer mutates calibrated state.** The old in-place `amax[amax == 0] = ...` wrote through a view of `self._amax`; `torch.where` returns a fresh tensor, so that hazard disappears. - **Warns, with a count.** The fix turns a loud failure into a silent one, and a zero amax means calibration never activated that layer — worth surfacing rather than papering over. The message reports how many entries were substituted, since per-location dedup otherwise collapses many dead experts into one uninformative message. A healthy model emits none. Scope: only the activation path is data-dependent and reachable this way. Weight-side `_amax` uses are left alone, since a weight amax of 0 would require an all-zero weight matrix. **Knowingly left as follow-up:** `export/quant_utils.py::get_scaling_factor` discards the sanitized `amax` when `num_bits == (2, 1)` and recomputes via `get_weights_scaling_factor_2_from_quantizer`, which reads `weight_quantizer._amax` raw — so a dynamic-NVFP4 *input* quantizer on a module whose *weight* quantizer is a different format (or disabled) can still trip `assert torch.all(scaling_factor > 0)`. Format dispatch is weight-driven, so the reported recipe does not reach that branch; fixing it properly changes a signature shared with the weight-side callers and is out of scope here. Not a regression. The dynamic early return, the `type: dynamic` numerics unit, and the recipe that combines them all ship in released 0.46.0 / 0.46.1. ### Usage No new or changed API. Exports that previously aborted now complete and warn: ```python # Recipe applies dynamic NVFP4 to *mlp*input_quantizer; layer 37 never activated during calibration. mtq.quantize(model, quant_cfg, forward_loop) export_hf_checkpoint(model, export_dir=out) # before: AssertionError; now: exports + UserWarning ``` ### Testing - New `test_amax_export_unusable_amax`, parametrized over zero and NaN, covering the dynamic-NVFP4 and static per-tensor configs; asserts the exported scale is positive and that export leaves the calibrated `amax` untouched. Plus `test_amax_export_meta_amax`, pinning that a meta `amax` survives export rather than raising. Both run on CPU and CUDA via the shared tester. - `tests/unit/torch/quantization/test_tensor_quantizer_cpu.py` — 40 passed. `tests/gpu/torch/quantization/test_tensor_quantizer_cuda.py` — 40 passed (GB300). - End-to-end repro on GB300, small Llama with one MLP fed all-zero activations under `general/ptq/nvfp4_mlp_only-kv_fp8_cast`: dead layer `export_amax()` `0.0` → `6.0`, live layer unchanged at `3.921875`, and `export_hf_checkpoint` goes from the `AssertionError` above to writing `model.safetensors`. - Full `examples/hf_ptq/hf_ptq.py` with the reported recipe and flags on a healthy model (Qwen3-0.6B): exits 0 and writes the checkpoint, confirming the normal path is unaffected. - `pre-commit run` clean on all changed files. ### 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`: N/A - Did you write any new necessary tests?: ✅ - Did you update [Changelog](https://github.com/NVIDIA/Model-Optimizer/blob/main/CHANGELOG.rst)?: ✅ - Did you get Claude approval on this PR?: ✅ — `/claude review` run; its one IMPORTANT finding (meta-tensor regression) and both SUGGESTIONs addressed or answered in 251f2e3d ### Additional Information Fixes NVBug 6768300, reported against 0.47.0rc1 on GB200. The reporter also notes it passed on 0.47.0rc0; that is not explained by code — `git diff 0.47.0rc0..0.47.0rc1` touches `export/quant_utils.py` only in `get_kv_cache_scaling_factor` (new `clamp_fp8_scales` argument whose default preserves the old behaviour) and the INT4-AWQ packing path, neither of which is on the dense-HF NVFP4 activation-scale path. Whether `amax` lands on exactly 0 is calibration/model-state dependent, which is what makes it look version-flaky. Worth flagging separately: in the reported log the **pre-PTQ** sample output is already gibberish, so that BF16 checkpoint looks broken independently of quantization. This change stops the crash, but such a run will now export a valid-but-garbage checkpoint — the new warning is the signal to investigate. Suggest the `cherry-pick-0.47.0` label so this lands in the ongoing release. 🤖 Generated with [Claude Code](https://claude.com/claude-code) <!-- This is an auto-generated comment: release notes by coderabbit.ai --> ## Summary by CodeRabbit * **Bug Fixes** * Fixed Hugging Face checkpoint export when dynamic-block quantizers have zero or invalid calibration scales. * Exports now use a positive fallback scale and issue a warning instead of failing when applicable. * Export operations no longer modify the original calibrated quantizer state. * Meta-device exports remain non-erroring and preserve device placement. * **Tests** * Added coverage for zero- and invalid-scale exports across dynamic and static quantization modes. <!-- end of auto-generated comment: release notes by coderabbit.ai --> Signed-off-by: Yue <yueshen@nvidia.com> Co-authored-by: Claude Opus 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 | Examples | Docs |
|---|---|---|---|
| Post Training Quantization | Compress model size by 2x-4x, speeding up inference while preserving model quality! | [HF LLMs / VLMs] [Megatron-Bridge LLMs / VLMs] [Diffusers] [ONNX] [Windows] | [docs] |
| Quantization Aware Training / Distillation | Refine accuracy of quantized models even further with a few training steps! | [Hugging Face] [Megatron-Bridge] | [docs] |
| Pruning | Reduce your model parameters or memory footprint and accelerate inference by removing unnecessary weights! | [General] [Megatron-Bridge] | |
| Distillation | Reduce deployment model size by teaching small models to behave like larger models! | [Hugging Face] [Megatron-Bridge] [Megatron-LM] | [docs] |
| Speculative Decoding | Train draft modules to predict extra tokens during inference! | [Hugging Face] [Megatron-LM] | [docs] |
| Sparsity | Efficiently compress your model by storing only its non-zero parameter values and their locations | [Hugging Face] | [docs] |
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!