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Support transformers 5.15-5.18 (<5.19) and drop DBRX - #2649

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kmorabia/bump-transformers-5.18
Oct 6, 2026
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kevalmorabia97 merged 7 commits into
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kmorabia/bump-transformers-5.18

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@kevalmorabia97 kevalmorabia97 commented Oct 2, 2026 •

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What does this PR do?

Type of change: new feature (dependency bump), bug fix, backward breaking (DBRX removal)

Extends the supported transformers range to >=4.57,<5.19 and moves CI's tf_latest to 5.18 (the latest release). It also fixes everything in 5.15–5.18 that breaks ModelOpt; each fix keeps 4.57–5.14 working. Separately, it removes DBRX support, and the customized-model quantization guide now uses Llama 4 as its example. Among other things, the HF side can now load glm5_next (GLM-5.3-Flash, native since 5.16.1).

  • Pins: the pyproject.toml hf extra, the "not tested" warning in modelopt/torch/__init__.py, and noxfile.py tf_latest (~=5.14.0 → ~=5.18.0).
  • HF tensor-parallel quantization (5.16 rewrote TP on DTensors, #47579):
    • 5.16 removed the module-level _hf_tp_plan that ModelOpt used to recognize TP-sharded linears. A model loaded with tp_plan="auto" was therefore quantized as if unsharded: its forward failed on mixed Tensor/DTensor inputs.
    • Sharded linears are now recognized by a DTensor weight on the model's TP mesh (model._device_mesh): Shard(0) is colwise and Shard(1) is rowwise. Matching the mesh (by ==) keeps FSDP2 shards out. The mesh is found on any submodule, so a model held by a trainer, PEFT or a wrapper still works, and ModelOpt warns if a TP mesh exists but no linear matched.
    • HF now installs its TP input/output transforms as an instance forward, which DynamicModule.convert keeps as _forward_pre_dm. HFParallelLinear.forward routes through it, and sets HF's _hf_quantized_needs_local_tp so the quantized linear runs on this rank's plain weight shard, in training as well.
    • The weight-access dispatch in core_utils.py now keys on the layer's own enable_weight_access_and_writeback instead of _hf_tp_plan.
  • DBRX support removed (internally agreed): the DBRX quantization plugin, its model spec, its unified-export preparation handler, the TRT-LLM export branches, and the AutoQuantize rules for its rewritten experts. This also drops the 5.0–5.14 vs 5.15+ expert-layout split that 5.15 would otherwise have needed. The customized-model quantization guide now uses the shipped Llama4TextExperts plugin (fused torch.bmm experts) as its example instead of DBRX. There is a Deprecations entry in the changelog.
  • TrainingArguments.warmup_ratio removed (5.15, #46917):
    • ModelOptArgParser now accepts either spelling in YAML configs and translates to whichever the installed transformers supports. warmup_ratio becomes warmup_steps on 5.15+, where a value below 1 is a ratio. A fractional warmup_steps becomes warmup_ratio on 4.x, where warmup_steps is an int.
    • The llm_qat train configs now use warmup_steps. They failed to parse on 5.15+.
    • examples/alpamayo/qad.py picks the supported key.
  • Puzzletron Qwen3-VL (5.17, #48105): Qwen3VLMoeVisionRotaryEmbedding now takes the vision config instead of dim, so the descriptor builds it from the config there. The old call raised AttributeError: 'int' object has no attribute 'rope_parameters'.
  • Alpamayo: the prompt cache is cropped with a negative count, since positive absolute-size crop() calls are deprecated (#47720).
  • Liger eval in ModelOpt's trainers: 5.15+ adds skip_logits=True to eval inputs when use_liger_kernel is set.
    • ModelOpt computes the fused (KD) loss itself from hidden states, and its compute_loss_func makes the Trainer pop labels. So the student's and the teacher's Liger forwards raised skip_logits is True, but labels and shift_labels are None.
    • This failed llm_qat QAT, QAD and QLoRA in CI. The flag is now dropped in both paths.

Checked, no change needed:

  • T5 (#47014): T5 now dispatches through ALL_ATTENTION_FUNCTIONS, so it registers with the generic _QuantAttention. FP8 KV-cache scales calibrate on 5.18, and _T5QuantAttention stays for 4.57–5.14.
  • Indexer layer types (#48974): remapped to indexed_attention. ModelOpt never compares these strings.
  • min_pixels / max_pixels (#49021): ModelOpt passes them only to from_pretrained, which is still supported.
  • No ModelOpt usage: the removed mask functions, update_candidate_strategy, and use_mamba_kernels.

Usage

pip install -U "nvidia-modelopt[hf]"   # now resolves transformers 5.18

Testing

All on this host (Python 3.13, torch 2.14). The 3.12 nox session can't start here because the system Python has a libffi/_ctypes mismatch, which is unrelated.

  • nox -s "unit-3.13(torch_214, tf_latest)" on 5.18, before the fixes: 4532 passed, 1 failed (test_dbrx, whose model is now removed).
    • With the fixes, tests/unit/torch/quantization + tests/unit/torch/opt on 5.18: 1414 passed, 8 skipped.
    • tests/unit/torch/quantization/plugins/test_huggingface.py: passes on 5.14.1 and 5.18.0.
  • tests/gpu/torch/quantization/plugins/test_transformers_tp.py (2 GPUs): passes on 5.14.1, 5.16.1 and 5.18.0.
    • It now also asserts that every sharded decoder linear is quantized as a TP-aware layer.
    • Without the fix it fails on 5.18 with aten.mm.default got mixed torch.Tensor and DTensor.
  • tests/examples/llm_qat/test_llm_qat.py on 5.18 (2 GPUs): QAT on DDP, QAD on FSDP2, and QLoRA pass.
    • QAT and QAD ran with attn_implementation: sdpa locally, because flash-attn doesn't build on this host.
    • Without the skip_logits fix, QAD on FSDP2 reproduces the CI error on both ranks.
  • test_transformers_tp wrapped-model case: fails with the old top-level mesh lookup and passes with the fix, on 5.14.1 and 5.18.0.
  • After removing DBRX: tests/unit/torch on 5.18: 3355 passed, 15 skipped. The test_dbrx cases are gone, the spec tests that used DBRX now use qwen3_5_moe, and the DBRX cases in the export-registry test are dropped.
  • Guide snippet: on 5.18, with ModelOpt's own Llama4 plugin unregistered, the guide's _QuantLlama4TextExperts inserts the same 4 quantizers on a tiny Llama4TextExperts and matches the shipped plugin's FP8 output exactly.
  • Warmup keys:
    • New test_yaml_warmup_spelling_follows_transformers covers both translation directions.
    • Parsing llm_qat/configs/train/qat_nvfp4.yaml and a legacy warmup_ratio: 0.05 YAML through llm_qat's TrainingArguments on 5.18 gives warmup_steps 0.05 for both.
    • ARGUMENTS.md regenerates unchanged. Its pre-commit hook couldn't run on this host because the hook's uv env has no torch, so I generated it manually and diffed.
  • Puzzletron: on a tiny Qwen3-VL-MoE, init_rotary_embedding reproduces the model's own vision inv_freq on both 5.14.1 and 5.18.0.
  • Alpamayo crop: keeps exactly the prefill tokens on both 5.14.1 and 5.18.0.
  • Not run locally: the full GPU and example suites, including the Puzzletron GPU test. CI covers them with the new tf_latest pin.

Before your PR is "Ready for review"

  • Is this change backward compatible?: ❌ DBRX is no longer supported. Otherwise, behavior on transformers 4.57–5.14 is unchanged and 5.15–5.18 are newly supported. llm_qat configs move from warmup_ratio to warmup_steps, but ModelOptArgParser still accepts warmup_ratio on every version.
  • 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?: ✅ Warmup-key translation, and the TP test now asserts TP-aware conversion (also for a wrapped model).
  • Did you update Changelog?: ✅ A Deprecations entry for the DBRX removal. The upper-bound bump itself gets none, as in Bump transformers dependency to >=4.57,<5.15 #2050.
  • Did you get Claude approval on this PR?: ❌

Additional Information

uv.lock is left to the weekly relock job. Example-specific pins (examples/speculative_decoding, examples/puzzletron, examples/windows/*) are left as they are; they pin for their own reasons.

Follow-up opportunities from the new releases, not in this PR:

  • Real tiny glm5_next / step3p7 models in the recipe tests, which would need a skip on the 4.57 CI leg.
  • HF-side KDA quantization (KimiLinear is native since 5.17).
  • NemotronH Omni support in hf_ptq.
  • Measuring hf_ptq calibration speed now that linear-attention kernels are opt-in (#47630).

🤖 Generated with Claude Code

Summary by CodeRabbit

  • Compatibility
    • Expanded supported Hugging Face Transformers versions to 4.57–5.18.
    • Added compatibility with newer Transformers tensor-parallel layers and Qwen3-VL vision embedding APIs.
    • Improved compatibility with Liger fused-loss evaluation during training and distillation.
  • Bug Fixes
    • Improved handling of warmup settings across Transformers versions.
    • Corrected sequence cropping during Alpamayo quantization.
  • Breaking Changes
    • Removed built-in DBRX quantization and TensorRT-LLM export support. DBRX quantization remains available in ModelOpt 0.47; custom plugin support can be added.

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📝 Walkthrough

Walkthrough

The pull request updates Transformers compatibility for tensor-parallel quantization and training arguments. It removes built-in DBRX quantization and export support. It also adjusts loss input filtering and model examples.

Changes

Hugging Face quantization compatibility

Layer / File(s) Summary
Transformers support for parallel linears
modelopt/torch/__init__.py, pyproject.toml, noxfile.py, modelopt/torch/quantization/plugins/huggingface.py, modelopt/torch/quantization/utils/core_utils.py, tests/gpu/torch/quantization/plugins/test_transformers_tp.py
The supported Transformers range extends to versions below 5.19, and the latest test pin changes to 5.18. Parallel linear compatibility recognizes 5.16+ DTensor layouts. Weight access uses a module-provided method, and tests cover direct and wrapped models.
Remove built-in DBRX quantization
modelopt/torch/quantization/plugins/huggingface.py, modelopt/torch/quantization/algorithms.py, modelopt/torch/models/*, tests/unit/torch/quantization/plugins/test_huggingface.py, tests/unit/torch/models/test_model_specs.py, docs/source/guides/_customized_model_quantization.rst, plugins/modelopt/skills/ptq/references/unsupported-models.md
DBRX quantization wrappers, registrations, model specs, and related grouping rules and tests are removed. The guide describes adding support with a custom plugin.

Training argument and loss compatibility

Layer / File(s) Summary
Warmup key translation and validation
modelopt/torch/opt/plugins/transformers.py, tests/unit/torch/opt/plugins/test_modelopt_arg_parser.py, examples/llm_qat/configs/train/*, examples/alpamayo/qad.py
YAML parsing maps warmup keys to options supported by the active parser. Tests cover newer and legacy argument formats. Training configurations use warmup_steps, and training_kwargs selects an available warmup argument.
Liger and distillation loss inputs
modelopt/torch/opt/plugins/transformers.py, modelopt/torch/distill/plugins/huggingface.py
The Liger fused-loss and knowledge-distillation paths remove skip_logits from inputs passed to the parent loss or student model.

Model example compatibility

Layer / File(s) Summary
Vision rotary initialization and cache cleanup
modelopt/torch/puzzletron/anymodel/models/qwen3_vl/qwen3_vl_model_descriptor.py, examples/alpamayo/quantize.py
Rotary-embedding initialization checks whether the constructor accepts a config parameter. Cache cleanup crops the number of tokens appended after prefill when that count is positive.

DBRX export support removal

Layer / File(s) Summary
Remove DBRX export paths
modelopt/torch/export/*, modelopt/torch/models/*, tests/unit/torch/export/test_export_registry.py, CHANGELOG.rst, docs/source/guides/_customized_model_quantization.rst, plugins/modelopt/skills/ptq/references/unsupported-models.md, examples/hf_ptq/hf_ptq.py
DBRX-specific export handlers, TensorRT-LLM mappings, and conversion paths are removed. The changelog and documentation describe the custom-plugin option. The no-quantization export path no longer rejects DBRX by model type.

Priority: ➖ Normal

Estimated code review effort: 4 (Complex) | ~50 minutes

Change: Feature

Merge Risk: ⚪ Minimal · up to 6f38d

The compatibility change interprets fractional warmup steps for newer Transformers. In the verified legacy version, positive warmup steps already took precedence over the ratio, so the cited configuration does not establish a lost effective ratio. No actionable merge risk remains beyond normal checks.

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Docstring Coverage ⚠️ Warning Docstring coverage is 56.41% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 39 functions across 18 files. (2 skipped:… Write docstrings for the functions missing them to satisfy the coverage threshold.
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Check name Status Explanation
Linked Issues check ✅ Passed Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check ✅ Passed Check skipped because no linked issues were found for this pull request.
Security Anti-Patterns ✅ Passed No listed security anti-pattern was introduced. The changed Python additions in modelopt/ and examples/ contain no unsafe torch.load, numpy.load(..., allow_pickle=True), hardcoded `trust_remot…
Description Check ✅ Passed Check skipped - CodeRabbit’s high-level summary is enabled.
Title check ✅ Passed The title clearly summarizes the two main changes: support for Transformers 5.15–5.18 and removal of DBRX support.
Full details: Docstring Coverage

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Codecov Report

❌ Patch coverage is 70.45455% with 13 lines in your changes missing coverage. Please review.
✅ Project coverage is 78.41%. Comparing base (01e3a30) to head (e91d002).
⚠️ Report is 1 commits behind head on main.

Files with missing lines Patch % Lines
modelopt/torch/quantization/plugins/huggingface.py 55.00% 9 Missing ⚠️
...model/models/qwen3_vl/qwen3_vl_model_descriptor.py 66.66% 2 Missing ⚠️
modelopt/torch/export/trtllm/layer_utils.py 50.00% 1 Missing ⚠️
modelopt/torch/quantization/utils/core_utils.py 50.00% 1 Missing ⚠️
Additional details and impacted files
@@            Coverage Diff             @@
##             main    #2649      +/-   ##
==========================================
+ Coverage   69.19%   78.41%   +9.21%     
==========================================
  Files         620      618       -2     
  Lines       69654    69584      -70     
==========================================
+ Hits        48197    54564    +6367     
+ Misses      21457    15020    -6437     
Flag Coverage Δ
examples-diffusers 21.05% <27.27%> (-0.02%) ⬇️
examples-gpt-oss 13.42% <4.54%> (-0.05%) ⬇️
examples-hf_ptq 22.86% <29.54%> (-0.05%) ⬇️
examples-llm_distill 13.48% <6.81%> (-0.04%) ⬇️
examples-llm_eval 17.39% <27.27%> (-0.02%) ⬇️
examples-llm_qat 17.55% <45.45%> (-0.02%) ⬇️
examples-llm_sparsity 15.82% <4.54%> (-0.03%) ⬇️
examples-megatron_bridge 26.77% <22.72%> (-0.15%) ⬇️
examples-specdec_bench 13.19% <4.54%> (-0.03%) ⬇️
examples-speculative_decoding 17.73% <27.27%> (-0.09%) ⬇️
examples-torch_onnx 21.60% <27.27%> (-0.02%) ⬇️
examples-torch_trt 15.21% <27.27%> (-0.03%) ⬇️
examples-vllm_serve 13.66% <4.54%> (-0.03%) ⬇️
gpu 58.38% <36.36%> (+36.75%) ⬆️
regression 15.08% <4.54%> (-0.03%) ⬇️
unit 58.60% <59.09%> (-0.04%) ⬇️

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@kevalmorabia97
kevalmorabia97 requested review from a team as code owners October 3, 2026 11:13
@kevalmorabia97 kevalmorabia97 changed the title Bump transformers support to <5.19 (5.18) and fix DBRX experts for 5.15+ Bump transformers support to <5.19 (5.18) and handle 5.15-5.18 breaking changes Oct 3, 2026

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Inline comments:
Review comments at @modelopt/torch/opt/plugins/transformers.py:
- Line 328: Update the legacy warmup-key translation so warmup_steps does not
silently overwrite an explicit warmup_ratio; define precedence or reject
conflicting values, and add a test covering both keys with different values.

Review comments at @modelopt/torch/quantization/plugins/huggingface.py:
- Line 585: Update the `tp_mesh` matching around the `_device_mesh` lookup so
multidimensional TP weights match the `"tp"` submesh by mesh dimension and rank
group rather than object identity, while preserving full-mesh matching for
one-dimensional TP.

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📒 Files selected for processing (14)
  • examples/alpamayo/qad.py
  • examples/alpamayo/quantize.py
  • examples/llm_qat/configs/train/finetune.yaml
  • examples/llm_qat/configs/train/qad_nvfp4.yaml
  • examples/llm_qat/configs/train/qad_scale_only.yaml
  • examples/llm_qat/configs/train/qad_with_learnt_amax.yaml
  • examples/llm_qat/configs/train/qat_nvfp4.yaml
  • examples/llm_qat/configs/train/qlora_nvfp4.yaml
  • modelopt/torch/opt/plugins/transformers.py
  • modelopt/torch/puzzletron/anymodel/models/qwen3_vl/qwen3_vl_model_descriptor.py
  • modelopt/torch/quantization/plugins/huggingface.py
  • modelopt/torch/quantization/utils/core_utils.py
  • tests/gpu/torch/quantization/plugins/test_transformers_tp.py
  • tests/unit/torch/opt/plugins/test_modelopt_arg_parser.py

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Comment thread modelopt/torch/opt/plugins/transformers.py
Comment thread modelopt/torch/quantization/plugins/huggingface.py Outdated
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/claude review Scope: only modelopt/ (quantization/plugins/huggingface.py, quantization/utils/core_utils.py, opt/plugins/transformers.py, puzzletron/.../qwen3_vl_model_descriptor.py, torch/__init__.py); skip tests/, examples/ and config pins. Recent runs have timed out at the 30-minute job limit.

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Bot review (bedrock-claude-opus-5-5) — DM the bot to share feedback.

LGTM: the fixes for transformers 5.15–5.18 look correct and keep the 4.57–5.14 paths. A human needs to sign off on the justified edit to the existing test_dbrx test.

Needs action:

  • Sign off on the test_dbrx edit in tests/unit/torch/quantization/plugins/test_huggingface.py. The assertions now branch on _DBRX_TRANSPOSED_EXPERTS because 5.15 changed DBRX's expert orientation. They still check exact equality, so the test wasn't loosened.

No action needed:

  • The design-review gate fired only on directory count. This is a dependency bump with targeted compatibility fixes, and it adds no new abstraction.
  • I checked the DBRX re-layout math for both orientations, and the _translate_warmup_keys cases on 4.x, 5.0–5.14 and 5.15+. Both are correct.
  • _forward_pre_dm comes from DynamicModule.convert. The new core_utils.py check only matches HF parallel linears, because no other class defines enable_weight_access_and_writeback.
  • HFParallelLinear.is_compatible compares meshes by identity (weight.device_mesh is tp_mesh). A TP sub-mesh of a 2-D mesh would be silently skipped. The new TP-test assertion would catch that for plain TP.
  • I read the tests but didn't run them. The GPU TP test was run by the author.

Comment thread modelopt/torch/quantization/plugins/huggingface.py
@kevalmorabia97
kevalmorabia97 requested a review from a team as a code owner October 4, 2026 20:01
@kevalmorabia97
kevalmorabia97 requested review from a team as code owners October 5, 2026 20:57
@kevalmorabia97 kevalmorabia97 changed the title Bump transformers support to <5.19 (5.18) and handle 5.15-5.18 breaking changes Bump transformers support to <5.19 (5.18), handle 5.15-5.18 breaking changes, and drop DBRX Oct 5, 2026
@kevalmorabia97 kevalmorabia97 changed the title Bump transformers support to <5.19 (5.18), handle 5.15-5.18 breaking changes, and drop DBRX Support transformers 5.15-5.18 (<5.19) and drop DBRX Oct 5, 2026
@kevalmorabia97
kevalmorabia97 deleted the kmorabia/bump-transformers-5.18 branch October 6, 2026 08:29
shengliangxu added a commit that referenced this pull request Oct 6, 2026
DBRX support was removed in #2649; use Llama4's fused BMM experts as the example instead.

Signed-off-by: Shengliang Xu <shengliangx@nvidia.com>
shengliangxu added a commit that referenced this pull request Oct 6, 2026
DBRX support was removed in #2649; use Llama4's fused BMM experts as the example instead.

Signed-off-by: Shengliang Xu <shengliangx@nvidia.com>
mxinO added a commit that referenced this pull request Oct 6, 2026
Apply the upstream datasets constraint from #2666 and Trackio update from #2649.

Signed-off-by: Meng Xin <mxin@nvidia.com>
shengliangxu added a commit that referenced this pull request Oct 6, 2026
DBRX support was removed in #2649; use Llama4's fused BMM experts as the example instead.

Signed-off-by: Shengliang Xu <shengliangx@nvidia.com>
shengliangxu added a commit that referenced this pull request Oct 6, 2026
DBRX support was removed in #2649; use Llama4's fused BMM experts as the example instead.

Signed-off-by: Shengliang Xu <shengliangx@nvidia.com>
shengliangxu added a commit that referenced this pull request Oct 6, 2026
)

### What does this PR do?

Type of change: Refactor

### Summary of the series

Model-specific PTQ modeling moves out of
`modelopt/torch/quantization/plugins/huggingface.py` into the per-model
packages under `modelopt/torch/models/<model_type>/modeling_ptq.py`,
next to each model's `specs.py`. By the end of the series
`huggingface.py` shrinks from ~2025 to ~1525 lines and keeps only the
code shared across models: sequential/fused MoE auto-detection,
attention, `FP8Linear`, `CompressedLinear`, parallel linears, and the
transposed-quantization helpers that gpt_oss and llama4 share. Model
types that gain PTQ modeling but had no `ModelSpec` get one.

- Class and function bodies move verbatim. The only rewrites: on-the-fly
callbacks are added to `CUSTOM_MODEL_PLUGINS` by their own module, and
`is_homogeneous_hf_model` imports `is_nemotron_h_model` lazily.
- `huggingface.py` imports every `modeling_ptq` from an explicit list.
The list sits after the generic wrappers these modules build on and
before the homogeneous decoder discoverer is registered, so Nemotron-H's
more specific discoverer still matches first.
- Each package's `__init__.py` keeps importing only `specs`, so `import
modelopt.torch.models` does not pull in quantization or transformers.
- No public API or quantization behavior changes; only private
(`_`-prefixed) names change module.

Merge in order. #2576 targets `main`; each later PR targets the one
before it.

1. #2576 — Add model specs for llama4, qwen3_vl_moe, falcon, step3p5 and
step3p7 ← **this PR**
2. #2577 — Add the `modeling_ptq.py` convention; move Nemotron-H, Falcon
and Llama4
3. #2578 — Move GPT-OSS and Qwen3-VL-MoE
4. #2580 — Move the Step family (step3p5, shared by step3p7)

The DBRX slice (#2579) was dropped: #2649 removed DBRX support, so there
was nothing left to move.

### This PR [1/4]

Registers a `ModelSpec` for each model type that gains `modeling_ptq.py`
later in the series but has no spec yet. Each spec records only facts
checked against transformers 4.57 and 5.14:

- `llama4` and `qwen3_vl_moe`: fused MoE layout
(`gate_up_proj`/`down_proj`), no gate/up pair, grouped export off. This
is data only: both blocks were already detected as MoE (structurally and
by name), and their expert containers are exported without name lookups.
- `falcon`: dense, no sections.
- `step3p5` / `step3p7`: `modeling_source="remote_code"` and
intentionally no `MoESpec`. Step's expert projections sit directly on
the MoE MLP with no `experts` container. Declaring the block would make
`is_moe` claim it and send AWQ export into `get_experts_list`, which
does not support that layout. `step3p7` gets its own package, following
the `gemma4_text` / `gemma4` precedent.

The exhaustive spec tables in
`tests/unit/torch/models/test_model_specs.py` (`EXPECTED_MOE_LAYOUTS`,
`root_class_names`) gain the two MoE rows.

### Usage

No API change. The new specs are read through the existing registry,
e.g. `get_spec("llama4").moe_spec`.

### Testing

Each branch of the stack checked out and tested with `pytest
tests/unit/torch/models tests/unit/torch/quantization
tests/unit/torch/export tests/unit/recipe` on CPU (torch 2.11,
transformers 5.14), on `main` at 9f902ae (#2649): 2248 passed, 7
skipped. The new block names resolve in `test_specs_vs_transformers.py`,
and the step3p5/step3p7 remote-code absence checks pass. Class names
were also checked against the transformers 4.57 wheel. GPU tests and the
transformers 4.57 matrix are left to CI.

### Before your PR is "*Ready for review*"

- Is this change backward compatible?: ✅ Only private (`_`-prefixed)
names change module; public API and quantization behavior are unchanged.
- 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?: ✅ Spec tables extended
(`EXPECTED_MOE_LAYOUTS`, `root_class_names`).
- Did you update
[Changelog](https://github.com/NVIDIA/Model-Optimizer/blob/main/CHANGELOG.rst)?:
N/A (internal refactor)
- Did you get Claude approval on this PR?: ❌

### Additional Information

Part of a 5-PR stack; see the series list above.

🤖 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 model support for Falcon, Llama 4, Qwen3-VL-MoE, Step-3.5, and
Step-3.7.
* Llama 4 and Qwen3-VL-MoE support includes recognition of their fused
expert layers.
* Falcon, Llama 4, and Qwen3-VL-MoE require Transformers 4.57 or later.
Step-3.5 and Step-3.7 use remote-code modeling.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

---------

Signed-off-by: Shengliang Xu <shengliangx@nvidia.com>
shengliangxu added a commit that referenced this pull request Oct 6, 2026
DBRX support was removed in #2649; use Llama4's fused BMM experts as the example instead.

Signed-off-by: Shengliang Xu <shengliangx@nvidia.com>
shengliangxu added a commit that referenced this pull request Oct 6, 2026
DBRX support was removed in #2649; use Llama4's fused BMM experts as the example instead.

Signed-off-by: Shengliang Xu <shengliangx@nvidia.com>
shengliangxu added a commit that referenced this pull request Oct 7, 2026
DBRX support was removed in #2649; use Llama4's fused BMM experts as the example instead.

Signed-off-by: Shengliang Xu <shengliangx@nvidia.com>
shengliangxu added a commit that referenced this pull request Oct 7, 2026
DBRX support was removed in #2649; use Llama4's fused BMM experts as the example instead.

Signed-off-by: Shengliang Xu <shengliangx@nvidia.com>
kevalmorabia97 added a commit that referenced this pull request Oct 7, 2026
### What does this PR do?

Type of change: backward breaking (dependency floor bump), cleanup

Raises the minimum transformers version from 4.57 to 5.5, so the
supported range becomes `>=5.5,<5.19`. CI's `tf_min` leg moves to
`transformers~=5.5.0`. It then removes the code that only existed for
transformers 4.x (or for 5.x releases older than 5.5).

**Why 5.5 and not higher:** TensorRT-LLM 1.3.0rc20 (CI's TRT-LLM
container) pins `transformers==5.5.4`. A higher floor makes pip upgrade
it inside that container. TRT-LLM then rejects the exported Qwen3-VL
checkpoint (`Unsupported rotary scaling type: axial`), which failed
`hf_ptq` CI on an earlier 5.8 revision of this PR. The CHANGELOG has had
a "transformers 4.x support will be dropped in a future release" note
since 0.46.

Follow-up to #2649, which extended the supported range up to 5.18.

- **Pins:** the `pyproject.toml` `hf` extra, the "not tested" warning in
`modelopt/torch/__init__.py`, and `noxfile.py` `tf_min`. `tf_min` drops
its `diffusers<0.40` and `datasets<5.1` (#2666) pins. Both only worked
around transformers 4.57's `huggingface_hub<1.0` cap, and 5.5 allows
`huggingface_hub>=1.0`.
- **Removed: dead version branches.** These include:
- `TRANSFORMERS_VERSION_GE_5_0` (quantization plugin) and
`_TRANSFORMERS_GE_5_0` (opt plugin).
- The 4.x paths in `_QuantSparseSequentialMoe`, the zero3 loader patch,
the tied-weights shim, and the expert-removal hook.
  - The 4.x-only direction of the warmup-key translation.
  - The `transformers<5.3` CVE warning.
- **Removed: dead workarounds.** On every supported version, these
either never ran or did nothing:
- `_QuantQwen3VLMoeTextExperts`. 5.5 already ships the fused
`Qwen3VLMoeTextExperts` layout, so it was never registered.
- The DFlash Qwen3-VL mRoPE workaround, which ran only on transformers
5.3.0, plus its tests.
- `_undo_torch_init_override_by_transformers`. 5.x moved
`TORCH_INIT_FUNCTIONS` out of `modeling_utils`, so this was a no-op from
5.0 on.
- The Puzzletron Qwen2/Qwen3/GPT-OSS dummy-block `attention_type`
copies. 5.5+ decoder layers have no `attention_type`.
  - `convert_file_size_to_int` import attempts (removed in 5.x).
- **Unguarded imports:** these now exist in every supported version:
- `Llama4TextExperts`, `FalconLinear`, `FP8Linear` and `GptOssExperts`
in the quantization plugin.
  - `conversion_mapping` and `core_model_loading` in `model_load_utils`.
- **Updated:**
- Model specs clamp `min_transformers_version` to the new 5.5 floor
(DeepSeek-V4 keeps 5.8), as `modelopt/torch/models/README.md`
prescribes.
- Library `from_pretrained`/`from_config` calls use `dtype=` instead of
the `torch_dtype=` that 5.x deprecates.
- `examples/puzzletron/requirements.txt` drops `transformers<5.0`, which
would otherwise downgrade below the new floor.
- The `warmup_ratio` comments in the gpt-oss/llm_qat configs and
notebooks are gone.
- **Tests:**
- Tests that only ran on 4.x are rewritten or removed.
`TestQuantSparseSequentialMoe` now runs on a synthetic sequential MoE
block instead of 4.x's tiny Qwen3-MoE, so it runs again.
- `test_peft_flow` gets a looser tolerance (`atol` 1e-2 → 3e-2). It
already failed on 5.8 before this PR: 5.8 initializes the tiny GPT-OSS
with ~4.5x larger logits. Comparing the merged-weight INT8 model against
LoRA-on-quantized-base then exceeds 1e-2.

- **Sparse-MoE calibration fix (from review):** collapsing the version
branch left `_QuantSparseSequentialMoe` token forcing asserting
`gate.top_k`, which broke remote-code blocks that keep `top_k` on the
block or name the count `n_routed_experts`. Token forcing now resolves
both structurally. It also counts the first calibration batch, which the
lazy init used to drop. New layout and end-to-end `mtq.quantize`
regressions cover it.

**Not changed:**
- `_T5QuantAttention` stays: T5 moved to the attention interface only in
5.15.
- The `_hf_tp_plan` TP path stays: 5.5–5.15 still use it.
- `warmup_ratio` → `warmup_steps` translation stays: 5.15 removed
`warmup_ratio`.
- `_QuantSparseSequentialMoe` and `register_sparse_moe_on_the_fly` stay:
remote-code MoEs still use per-expert `nn.Linear`.
- `_checkpoint_conversion_mapping` renames stay for remote code.
- Top-level `rope_theta` stays in the EAGLE default config: the Megatron
EAGLE plugin reads it.

### Usage

```bash
pip install -U "nvidia-modelopt[hf]"   # transformers>=5.5,<5.19
```

### Testing

All on this host (Python 3.13, torch 2.14, 2x RTX 6000 Ada), on this
branch.
- **Probe of 5.5.4, 5.8.1 and 5.18.0:** every unguarded import exists.
`Qwen3VLMoeTextExperts` already has the fused layout on 5.5.4.
`modeling_utils.TORCH_INIT_FUNCTIONS` and
`transformers.utils.convert_file_size_to_int` are gone. 5.5.4 still has
`warmup_ratio`, the `_hf_tp_plan` TP path and pre-interface T5.
- **5.5.4 (new floor):** `nox -s "unit-3.13(torch_214, tf_min)"` (fresh
env: transformers 5.5.4, `datasets` 5.1.0, `huggingface_hub` 1.33.0):
4506 passed, 38 skipped, 0 failed. `test_transformers_tp.py` (2 GPUs)
and `test_vllm_fakequant_hf_export.py`: 6 passed.
- **`tests/unit` on 5.8.1 (fresh nox env):** 4502 passed, 37 skipped, 0
failed.
- **`tests/unit` on 5.18.0:** 4530 passed, 9 skipped, 0 failed.
- **`tests/unit/torch/quantization` after the sparse-MoE fix:** 1346
passed on both 5.8.1 and 5.18.0. The 5 new sparse-MoE tests fail on
main's plugin and pass with the fix.
- **GPU on 5.8.1:** `test_transformers_tp.py` (2 GPUs) and
`test_vllm_fakequant_hf_export.py` pass (6 passed).
- **`tests/gpu/torch/puzzletron/test_puzzletron.py` on 5.18.0:** 7
passed, 2 skipped (no `mamba_ssm`). This covers the removed
Qwen2/Qwen3/GPT-OSS dummy-block overrides.
- On 5.8.1 the Llama/Mistral/Qwen2/Qwen3 cases fail their `lm_loss`
check, and main's code gives the same values. The expected losses are
tuned for 5.18.
- GPU CI installs the newest allowed transformers, so it isn't affected.
- **Not run:** `test_nemotron_h_gpu_validation.py` (no `mamba-ssm` here)
and the example suites.

### Before your PR is "*Ready for review*"

- Is this change backward compatible?: ❌ transformers 4.57–5.4 is no
longer supported.
- 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?: ✅ The sparse sequential MoE
tests are rewritten so they run on 5.x.
- Did you update
[Changelog](https://github.com/NVIDIA/Model-Optimizer/blob/main/CHANGELOG.rst)?:
✅ Backward Breaking Changes.
- Did you get Claude approval on this PR?: ❌

### Additional Information

Users still pinning transformers 4.x in this repo, left as is (owners to
decide):
- The speculative-decoding MiniMax-M2.7 DFlash flow
(`OVERRIDE_TRANSFORMERS=4.57.x`, `fsdp2_buffer_patch.py`,
`tools/launcher/examples/MiniMax/MiniMax-M2.7-DFlash`).
- The launcher's Nemotron-3-Nano `mbridge_prune.yaml` (`transformers<5`
on `nemo:26.04`).
- `examples/windows/*` (ONNX flows, `transformers<5.0` / `==4.57.3`).
- `experimental/dms` (standalone, pins 4.57.3).

`uv.lock` is left to the weekly relock job.

🤖 Generated with [Claude Code](https://claude.com/claude-code)


<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

* **Breaking Changes**
* Transformers 5.5 or later is now required; Transformers 4.x is
unsupported.
* Layerwise calibration now uses quantized activations from the previous
layer by default. This can be configured.
* **Improvements**
* Updated checkpoint handling for DeepSeek-V4 indexers and unexpected
weights during Hugging Face post-training quantization.
  * Updated Megatron distillation loss behavior and configuration.
* Improved model loading and export compatibility with supported
Transformers versions.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

---------

Signed-off-by: Keval Morabia <28916987+kevalmorabia97@users.noreply.github.com>
Co-authored-by: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
shengliangxu added a commit that referenced this pull request Oct 8, 2026
DBRX support was removed in #2649; use Llama4's fused BMM experts as the example instead.

Signed-off-by: Shengliang Xu <shengliangx@nvidia.com>
shengliangxu added a commit that referenced this pull request Oct 8, 2026
DBRX support was removed in #2649; use Llama4's fused BMM experts as the example instead.

Signed-off-by: Shengliang Xu <shengliangx@nvidia.com>
shengliangxu added a commit that referenced this pull request Oct 8, 2026
DBRX support was removed in #2649; use Llama4's fused BMM experts as the example instead.

Signed-off-by: Shengliang Xu <shengliangx@nvidia.com>
shengliangxu added a commit that referenced this pull request Oct 8, 2026
)

### What does this PR do?

Type of change: Refactor

### Summary of the series

Model-specific PTQ modeling moves out of
`modelopt/torch/quantization/plugins/huggingface.py` into the per-model
packages under `modelopt/torch/models/<model_type>/modeling_ptq.py`,
next to each model's `specs.py`. By the end of the series
`huggingface.py` shrinks from ~1880 to ~1500 lines and keeps only the
code shared across models: sequential/fused MoE auto-detection,
attention, `FP8Linear`, `CompressedLinear`, parallel linears, and the
transposed-quantization helpers that gpt_oss and llama4 share. Model
types that gain PTQ modeling but had no `ModelSpec` get one.

- Class and function bodies move verbatim. The only rewrites: on-the-fly
callbacks are added to `CUSTOM_MODEL_PLUGINS` by their own module, and
`is_homogeneous_hf_model` imports `is_nemotron_h_model` lazily.
- `huggingface.py` imports every `modeling_ptq` from an explicit list.
The list sits after the generic wrappers these modules build on and
before the homogeneous decoder discoverer is registered, so Nemotron-H's
more specific discoverer still matches first.
- Each package's `__init__.py` keeps importing only `specs`, so `import
modelopt.torch.models` does not pull in quantization or transformers.
- No public API or quantization behavior changes; only private
(`_`-prefixed) names change module.

Merge in order. #2576 targets `main`; each later PR targets the one
before it.

1. #2576 — Add model specs for llama4, qwen3_vl_moe, falcon, step3p5 and
step3p7
2. #2577 — Add the `modeling_ptq.py` convention; move Nemotron-H, Falcon
and Llama4 ← **this PR**
3. #2578 — Move GPT-OSS
4. #2580 — Move the Step family (step3p5, shared by step3p7)

The DBRX slice (#2579) was dropped: #2649 removed DBRX support, so there
was nothing left to move. Likewise, the Qwen3-VL-MoE half of [3/4] was
dropped: #2670 removed its pre-5.12 wrapper.

### This PR [2/4]

Introduces `<model_type>/modeling_ptq.py` and moves the first three
models there:

- `nemotron_h`: `is_nemotron_h_model` / `get_nemotron_h_decoder_layers`
and their layerwise-calibration registration.
- `falcon`: the `FalconLinear` registration and
`register_falcon_linears_on_the_fly`.
- `llama4`: `_QuantLlama4TextExperts` and its registration.

The registrations move in the form #2670 gave them (a top-level
transformers import plus `if ... not in QuantModuleRegistry`), and
`huggingface.py` drops the imports it no longer uses. It also adds the
`importlib` loop in `huggingface.py` that imports each `modeling_ptq`,
documents the convention in `modelopt/torch/models/README.md` and the
package docstring, and adds
`tests/unit/torch/models/test_modeling_ptq_registration.py`, which
checks in a fresh interpreter per case that registration does not depend
on which module is imported first.

It also raises the `llama4`, `qwen3_vl_moe` and `falcon` specs from
#2576 to the transformers 5.5 floor that #2670 set for every other spec,
and drops the `qwen3_vl_moe` spec's pointer to the pre-5.12 wrapper
#2670 removed.

### Usage

No API change. To add PTQ support for a new model, put its wrapper in
`modelopt/torch/models/<model_type>/modeling_ptq.py` and add
`<model_type>` to the import loop at the end of
`quantization/plugins/huggingface.py`.

### Testing

Each branch of the stack checked out and tested on `main` at 90ba9fb,
CPU, torch 2.11. With transformers 5.18: `pytest tests/unit/torch/models
tests/unit/torch/quantization tests/unit/torch/export
tests/unit/recipe`, 2370 passed, 1 skipped. With transformers 5.5 (the
new floor): `tests/unit/torch/models` plus `test_moe_linear.py` and
`test_huggingface.py`, 205 passed, 1 skipped. GPU tests are left to CI.

### Before your PR is "*Ready for review*"

- Is this change backward compatible?: ✅ Only private (`_`-prefixed)
names change module; public API and quantization behavior are unchanged.
- 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?: N/A (verbatim move; covered by
existing tests)
- Did you update
[Changelog](https://github.com/NVIDIA/Model-Optimizer/blob/main/CHANGELOG.rst)?:
N/A (internal refactor)
- Did you get Claude approval on this PR?: ❌

### Additional Information

Part of a 5-PR stack; see the series list above.

🤖 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 post-training quantization support for Llama 4 expert layers.
* Expanded Falcon quantization coverage to include linear layers
discovered at runtime and older remote-code checkpoints.
* Added Nemotron-H model detection and decoder-layer discovery for
quantization.

* **Bug Fixes**
* Improved Qwen3-VL mixture-of-experts compatibility by applying the
legacy quantization wrapper only when needed.

* **Documentation**
* Clarified how model-specific quantization support is loaded and where
model support information belongs.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

---------

Signed-off-by: Shengliang Xu <shengliangx@nvidia.com>
shengliangxu added a commit that referenced this pull request Oct 8, 2026
DBRX support was removed in #2649; use Llama4's fused BMM experts as the example instead.

Signed-off-by: Shengliang Xu <shengliangx@nvidia.com>
shengliangxu added a commit that referenced this pull request Oct 9, 2026
DBRX support was removed in #2649; use Llama4's fused BMM experts as the example instead.

Signed-off-by: Shengliang Xu <shengliangx@nvidia.com>
shengliangxu added a commit that referenced this pull request Oct 9, 2026
…dels [3/4] (#2578)

### What does this PR do?

Type of change: Refactor

### Summary of the series

Model-specific PTQ modeling moves out of
`modelopt/torch/quantization/plugins/huggingface.py` into the per-model
packages under `modelopt/torch/models/<model_type>/modeling_ptq.py`,
next to each model's `specs.py`. By the end of the series
`huggingface.py` shrinks from ~1880 to ~1500 lines and keeps only the
code shared across models: sequential/fused MoE auto-detection,
attention, `FP8Linear`, `CompressedLinear`, parallel linears, and the
transposed-quantization helpers that gpt_oss and llama4 share. Model
types that gain PTQ modeling but had no `ModelSpec` get one.

- Class and function bodies move verbatim. The only rewrites: on-the-fly
callbacks are added to `CUSTOM_MODEL_PLUGINS` by their own module, and
`is_homogeneous_hf_model` imports `is_nemotron_h_model` lazily.
- `huggingface.py` imports every `modeling_ptq` from an explicit list.
The list sits after the generic wrappers these modules build on and
before the homogeneous decoder discoverer is registered, so Nemotron-H's
more specific discoverer still matches first.
- Each package's `__init__.py` keeps importing only `specs`, so `import
modelopt.torch.models` does not pull in quantization or transformers.
- No public API or quantization behavior changes; only private
(`_`-prefixed) names change module.

Merge in order. #2576 and #2577 have merged; #2578 now targets `main`,
and #2580 targets #2578's branch.

1. #2576 — Add model specs for llama4, qwen3_vl_moe, falcon, step3p5 and
step3p7 (merged)
2. #2577 — Add the `modeling_ptq.py` convention; move Nemotron-H, Falcon
and Llama4 (merged)
3. #2578 — Move GPT-OSS  ← **this PR**
4. #2580 — Move the Step family (step3p5, shared by step3p7)

The DBRX slice (#2579) was dropped: #2649 removed DBRX support, so there
was nothing left to move. Likewise, the Qwen3-VL-MoE half of [3/4] was
dropped: #2670 removed its pre-5.12 wrapper.

### This PR [3/4]

Moves `_QuantGptOssExperts` and its registration into
`gpt_oss/modeling_ptq.py`, adds `gpt_oss` to the import loop, and
extends the registration test to it. This slice originally also moved
the pre-5.12 Qwen3-VL-MoE wrapper; #2670 removed that wrapper, so that
half was dropped.

### Usage

No API change. To add PTQ support for a new model, put its wrapper in
`modelopt/torch/models/<model_type>/modeling_ptq.py` and add
`<model_type>` to the import loop at the end of
`quantization/plugins/huggingface.py`.

### Testing

Each branch of the stack checked out and tested on `main` at 90ba9fb,
CPU, torch 2.11. With transformers 5.18: `pytest tests/unit/torch/models
tests/unit/torch/quantization tests/unit/torch/export
tests/unit/recipe`, 2371 passed, 1 skipped. With transformers 5.5 (the
new floor): `tests/unit/torch/models` plus `test_moe_linear.py` and
`test_huggingface.py`, 206 passed, 1 skipped. GPU tests are left to CI.

### Before your PR is "*Ready for review*"

- Is this change backward compatible?: ✅ Only private (`_`-prefixed)
names change module; public API and quantization behavior are unchanged.
- 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?: N/A (verbatim move; existing
tests re-pointed)
- Did you update
[Changelog](https://github.com/NVIDIA/Model-Optimizer/blob/main/CHANGELOG.rst)?:
N/A (internal refactor)
- Did you get Claude approval on this PR?: ❌

### Additional Information

Part of a 5-PR stack; see the series list above.

🤖 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 post-training quantization support for GPT-OSS models.
* Added support for quantizing legacy Qwen3-VL-MoE layouts, while
retaining support for newer fused layouts.
* Quantization support now accommodates both legacy and newer
Qwen3-VL-MoE model layouts.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

---------

Signed-off-by: Shengliang Xu <shengliangx@nvidia.com>
shengliangxu added a commit that referenced this pull request Oct 9, 2026
DBRX support was removed in #2649; use Llama4's fused BMM experts as the example instead.

Signed-off-by: Shengliang Xu <shengliangx@nvidia.com>
shengliangxu added a commit that referenced this pull request Oct 9, 2026
…dels [4/4] (#2580)

### What does this PR do?

Type of change: Refactor

### Summary of the series

Model-specific PTQ modeling moves out of
`modelopt/torch/quantization/plugins/huggingface.py` into the per-model
packages under `modelopt/torch/models/<model_type>/modeling_ptq.py`,
next to each model's `specs.py`. By the end of the series
`huggingface.py` shrinks from ~1880 to ~1500 lines and keeps only the
code shared across models: sequential/fused MoE auto-detection,
attention, `FP8Linear`, `CompressedLinear`, parallel linears, and the
transposed-quantization helpers that gpt_oss and llama4 share. Model
types that gain PTQ modeling but had no `ModelSpec` get one.

- Class and function bodies move verbatim. The only rewrites: on-the-fly
callbacks are added to `CUSTOM_MODEL_PLUGINS` by their own module, and
`is_homogeneous_hf_model` imports `is_nemotron_h_model` lazily.
- `huggingface.py` imports every `modeling_ptq` from an explicit list.
The list sits after the generic wrappers these modules build on and
before the homogeneous decoder discoverer is registered, so Nemotron-H's
more specific discoverer still matches first.
- Each package's `__init__.py` keeps importing only `specs`, so `import
modelopt.torch.models` does not pull in quantization or transformers.
- No public API or quantization behavior changes; only private
(`_`-prefixed) names change module.

Merge in order. #2576, #2577 and #2578 have merged; this last slice,
#2580, now targets `main`.

1. #2576 — Add model specs for llama4, qwen3_vl_moe, falcon, step3p5 and
step3p7 (merged)
2. #2577 — Add the `modeling_ptq.py` convention; move Nemotron-H, Falcon
and Llama4 (merged)
3. #2578 — Move GPT-OSS (merged)
4. #2580 — Move the Step family (step3p5, shared by step3p7) ← **this
PR**

The DBRX slice (#2579) was dropped: #2649 removed DBRX support, so there
was nothing left to move. Likewise, the Qwen3-VL-MoE half of [3/4] was
dropped: #2670 removed its pre-5.12 wrapper.

### This PR [4/4]

Moves `_QuantMoELinear`, `_is_expert_indexed_moe_linear`,
`_is_step_family_model`, `register_moe_linear_on_the_fly` and
`_reconstruct_fused_moe_linear` into `step3p5/modeling_ptq.py`, which
also serves `step3p7`. This carries over #2569's switch of
`_is_step_family_model` to `hf_model_type`; `huggingface.py` drops its
now-unused `hf_model_type` and `re` imports.

Export (`hf_export_handlers.py`, `layerwise_export.py`,
`unified_export_hf.py`, `unified_export_hf_streaming.py`) imports these
names from the new module. The imports stay deferred, because
`modelopt.torch.quantization` imports `modelopt.torch.export` and
importing at module scope would risk an import cycle; the comments now
give that reason. The PTQ skill references (`unsupported-models.md`,
`checkpoint-validation.md`) now point agents at
`modelopt/torch/models/<model_type>/modeling_ptq.py` for model-specific
patches.

Rebasing onto #2649 also replaces the README's DBRX example of a
model-specific wrapper with Llama4's fused BMM experts.

`step3p7` also gets its own `modeling_ptq.py`, which imports the
Step-3.5 module: Step-3.7 remote-code checkpoints use the same
`MoELinear`, and today they are covered only because the HF plugin
imports every `modeling_ptq`. With its own module, a future loader that
imports PTQ modeling by model type finds it too.

### Usage

No API change. To add PTQ support for a new model, put its wrapper in
`modelopt/torch/models/<model_type>/modeling_ptq.py` and add
`<model_type>` to the import loop at the end of
`quantization/plugins/huggingface.py`.

### Testing

Each branch of the stack checked out and tested on `main` at 90ba9fb,
CPU, torch 2.11. With transformers 5.18: `pytest tests/unit/torch/models
tests/unit/torch/quantization tests/unit/torch/export
tests/unit/recipe`, 2372 passed, 1 skipped. With transformers 5.5 (the
new floor): `tests/unit/torch/models` plus `test_moe_linear.py` and
`test_huggingface.py`, 207 passed, 1 skipped. GPU tests are left to CI.

### Before your PR is "*Ready for review*"

- Is this change backward compatible?: ✅ Only private (`_`-prefixed)
names change module; public API and quantization behavior are unchanged.
- 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?: N/A (verbatim move; existing
tests re-pointed)
- Did you update
[Changelog](https://github.com/NVIDIA/Model-Optimizer/blob/main/CHANGELOG.rst)?:
N/A (internal refactor)
- Did you get Claude approval on this PR?: ❌

### Additional Information

Part of a 5-PR stack; see the series list above.

🤖 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 post-training quantization support for Step-family models with
expert-indexed MoE layers.
* Checkpoint exports preserve the original layout of quantized expert
weights and scales.
* **Documentation**
* Updated MoE architecture examples and guidance for configuring
model-specific quantization support, including Step model revisions.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

---------

Signed-off-by: Shengliang Xu <shengliangx@nvidia.com>
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