From a5c96362b6626a996b5a0af3fe06c5ef1ae4779b Mon Sep 17 00:00:00 2001
From: Mick <mickjagger19@icloud.com>
Date: Wed, 19 Aug 2026 13:36:55 +0800
Subject: [PATCH] [diffusion] chore: reuse shared checkpoint quant metadata
 resolver (#35174)

---
 .../runtime/loader/transformer_load_utils.py  |  2 +-
 .../runtime/utils/quantization_utils.py       | 19 ++++--------
 .../test/unit/test_transformer_quant.py       | 31 +++++++++++++++++++
 3 files changed, 38 insertions(+), 14 deletions(-)

diff --git a/python/sglang/multimodal_gen/runtime/loader/transformer_load_utils.py b/python/sglang/multimodal_gen/runtime/loader/transformer_load_utils.py
index 052545dd1..adebc8c2e 100644
--- a/python/sglang/multimodal_gen/runtime/loader/transformer_load_utils.py
+++ b/python/sglang/multimodal_gen/runtime/loader/transformer_load_utils.py
@@ -17,6 +17,7 @@ import torch
 from diffusers.utils import SAFE_WEIGHTS_INDEX_NAME
 from torch import nn
 
+from sglang.multimodal_gen.runtime.layers.quantization import QuantizationConfig
 from sglang.multimodal_gen.runtime.layers.quantization.configs.nunchaku_config import (
     NunchakuConfig,
     _patch_nunchaku_scales,
@@ -42,7 +43,6 @@ from sglang.multimodal_gen.runtime.utils.quantization_utils import (
     get_quant_config,
     get_quant_config_from_safetensors_metadata,
 )
-from sglang.srt.layers.quantization import QuantizationConfig
 
 logger = init_logger(__name__)
 
diff --git a/python/sglang/multimodal_gen/runtime/utils/quantization_utils.py b/python/sglang/multimodal_gen/runtime/utils/quantization_utils.py
index 10859b05c..e3a49f3f4 100644
--- a/python/sglang/multimodal_gen/runtime/utils/quantization_utils.py
+++ b/python/sglang/multimodal_gen/runtime/utils/quantization_utils.py
@@ -13,6 +13,9 @@ from sglang.multimodal_gen.runtime.layers.quantization import (
     get_quantization_config,
 )
 from sglang.multimodal_gen.runtime.utils.logging_utils import init_logger
+from sglang.srt.model_loader.checkpoint_quantization import (
+    resolve_checkpoint_quant_spec,
+)
 
 logger = init_logger(__name__)
 
@@ -169,27 +172,17 @@ def get_quant_config(
         quant_cls = _load_quant_cls(quant_cfg)
         return quant_cls.from_config(quant_cfg, reverse_param_names_mapping)
 
-    if "quantization_config" not in model_config:
+    checkpoint_quant_spec = resolve_checkpoint_quant_spec(model_config)
+    if checkpoint_quant_spec is None:
         return None
 
-    hf_quant_config = normalize_flat_modelopt_quant_config(
-        model_config["quantization_config"]
-    )
-    if hf_quant_config is not None and not isinstance(hf_quant_config, dict):
-        hf_quant_config = hf_quant_config.to_dict()
+    hf_quant_config = normalize_flat_modelopt_quant_config(checkpoint_quant_spec.config)
     quant_cls = _load_quant_cls(hf_quant_config)
 
     # GGUF doesn't have config file
     if hf_quant_config["quant_method"] == "gguf":
         return quant_cls.from_config({})
 
-    # some vision model may keep quantization_config in their text_config
-    hf_text_config = getattr(model_config, "text_config", None)
-    if hf_quant_config is None and hf_text_config is not None:
-        hf_quant_config = getattr(hf_text_config, "quantization_config", None)
-    if hf_quant_config is None:
-        # compressed-tensors uses a compressions_config
-        hf_quant_config = getattr(model_config, "compression_config", None)
     if hf_quant_config is not None:
         hf_quant_config["packed_modules_mapping"] = packed_modules_mapping
         is_modelopt_fp8 = (
diff --git a/python/sglang/multimodal_gen/test/unit/test_transformer_quant.py b/python/sglang/multimodal_gen/test/unit/test_transformer_quant.py
index d8d1131af..cb85d61de 100644
--- a/python/sglang/multimodal_gen/test/unit/test_transformer_quant.py
+++ b/python/sglang/multimodal_gen/test/unit/test_transformer_quant.py
@@ -490,6 +490,37 @@ class TestTransformerQuantHelpers(unittest.TestCase):
         self.assertTrue(config.load_in_4bit)
         self.assertEqual(config.bnb_4bit_quant_type, "nf4")
 
+    def test_fp8_quant_config_resolves_from_text_config(self):
+        config = get_quant_config(
+            {
+                "text_config": {
+                    "quantization_config": {
+                        "quant_method": "fp8",
+                        "activation_scheme": "dynamic",
+                    }
+                }
+            },
+            "/unused/component/path",
+        )
+
+        self.assertIsInstance(config, Fp8Config)
+        self.assertTrue(config.is_checkpoint_fp8_serialized)
+
+    def test_bitsandbytes_quant_config_resolves_from_compression_config(self):
+        config = get_quant_config(
+            {
+                "compression_config": {
+                    "quant_method": "bitsandbytes",
+                    "load_in_4bit": True,
+                    "bnb_4bit_quant_storage": "uint8",
+                }
+            },
+            "/unused/component/path",
+        )
+
+        self.assertEqual(config.get_name(), "bitsandbytes")
+        self.assertTrue(config.load_in_4bit)
+
     def test_nvfp4_safetensors_inference_ignores_fp8_fallback_scales(self):
         with tempfile.NamedTemporaryFile(suffix=".safetensors") as f:
             save_file(