Auto Quantize improvements and bug fixes for large sparse MoEs

- Add get_auto_quantize_config API to extract quant config from search results
- Save/restore calibration state in auto_quantize checkpoints
- Add NemotronH MoE expert support in auto_quantize grouping/scoring
- Fix SequentialQuantizer scope, use F.kl_div for numerical stability
- Fix mypy errors and clean up tests

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Signed-off-by: realAsma <akuriparambi@nvidia.com>

Author: realAsma

CHANGELOG.rst

@@ -21,6 +21,9 @@ NVIDIA Model Optimizer Changelog
 - ``pass_through_bwd`` in the quantization config is now default to True. Please set it to False if you want to use STE with zeroed outlier gradients for potentially better QAT accuracy.
 - Add :meth:`compute_quantization_mse <modelopt.torch.quantization.model_quant.compute_quantization_mse>` API to measure per-quantizer mean-squared quantization error, with flexible wildcard and callable filtering.
 - **AutoQDQ**: New tool for automated Q/DQ (Quantize/Dequantize) placement optimization for ONNX models. Uses TensorRT latency measurements to choose insertion schemes that minimize inference time. Discovers regions automatically, groups them by structural pattern, and tests multiple Q/DQ schemes per pattern. Supports INT8 and FP8 quantization, pattern cache for warm-start on similar models, checkpoint/resume, and importing patterns from an existing QDQ baseline. CLI: ``python -m modelopt.onnx.quantization.autotune``. See the AutoQDQ guide in the documentation.
+- Add ``get_auto_quantize_config`` API to extract a flat quantization config from ``auto_quantize`` search results, enabling re-quantization at different effective bit targets without re-running calibration.
+- Improve ``auto_quantize`` checkpoint/resume: calibration state is now saved and restored across runs, avoiding redundant calibration when resuming a search.
+- Add NemotronH MoE expert support in ``auto_quantize`` grouping and scoring rules.
 
 **Misc**
 

modelopt/torch/opt/searcher.py

@@ -236,33 +236,50 @@ def state_dict(self) -> SearchStateDict:
         """The state dictionary that can be stored/loaded."""
         return {key: getattr(self, key) for key in self.default_state_dict}
 
-    def load_search_checkpoint(self) -> bool:
+    def _get_checkpoint_path(self) -> str | None:
+        """Get per-rank checkpoint path when distributed, otherwise the original path."""
+        checkpoint = self.config["checkpoint"]
+        if checkpoint is None:
+            return None
+        if dist.is_initialized():
+            dirname, basename = os.path.split(checkpoint)
+            name, ext = os.path.splitext(basename)
+            return os.path.join(dirname, f"{name}{dist.rank()}{ext}")
+        return checkpoint
+
+    def load_search_checkpoint(self, strict=True) -> bool:
         """Load function for search checkpoint returning indicator whether checkpoint was loaded."""
-        # check if checkpoint exists
-        checkpoint: str | None = self.config["checkpoint"]
+        checkpoint = self._get_checkpoint_path()
         if checkpoint is None:
             return False
+        # Backward compat: fall back to the original single-file path
+        if not os.path.exists(checkpoint):
+            checkpoint = self.config["checkpoint"]
         if not os.path.exists(checkpoint):
             warn_rank_0(f"Checkpoint {checkpoint} does not exist! Initializing from scratch.")
             return False
 
-        # iterate through state dict and load keys
         print_rank_0(f"Loading searcher state from {checkpoint}...")
         # Security NOTE: weights_only=False is used here on ModelOpt-generated ckpt, not on untrusted user input
         state_dict = torch.load(checkpoint, weights_only=False)
-        assert state_dict.keys() == self.state_dict().keys(), "Keys in checkpoint don't match!"
-        for key, state in state_dict.items():
-            setattr(self, key, state)
+        if strict:
+            assert state_dict.keys() == self.state_dict().keys(), "Keys in checkpoint don't match!"
+        for key, default_val in self.default_state_dict.items():
+            setattr(self, key, state_dict.get(key, default_val))
         return True
 
     def save_search_checkpoint(self, verbose=False) -> None:
         """Save function for search checkpoint."""
-        # check if save requirements are satisfied
-        checkpoint: str | None = self.config["checkpoint"]
-        if checkpoint is None or not dist.is_master():
+        checkpoint = self._get_checkpoint_path()
+        if checkpoint is None:
             return
 
-        # save state dict
+        if dist.is_initialized():
+            warn_rank_0(
+                "torch.distributed is initialized. Please maintain the same parallelism "
+                "configuration (world size, TP, EP, etc.) across search save and restore sessions."
+            )
+
         if verbose:
             print(f"Saving searcher state to {checkpoint}...")
         save_dirname, _ = os.path.split(checkpoint)