[Model] Add SupportsMultiModal.get_language_model interface (#16007)

Signed-off-by: NickLucche <nlucches@redhat.com>

Author: NickLucche

docs/source/contributing/model/multimodal.md

@@ -79,6 +79,17 @@ Further update the model as follows:
             return inputs_embeds
     ```
 
+- Implement {meth}`~vllm.model_executor.models.interfaces.SupportsMultiModal.get_language_model` getter to provide stable access to the underlying language model.
+
+    ```python
+    class YourModelForImage2Seq(nn.Module):
+        ...
+
+        def get_language_model(self) -> torch.nn.Module:
+            # Change `language_model` according to your implementation.
+            return self.language_model
+    ```
+
 - Once the above steps are done, update the model class with the {class}`~vllm.model_executor.models.interfaces.SupportsMultiModal` interface.
 
   ```diff

vllm/model_executor/models/aria.py

@@ -605,6 +605,9 @@ def _process_image_input(
 
         return self.multi_modal_projector(image_outputs, image_attn_mask)
 
+    def get_language_model(self) -> torch.nn.Module:
+        return self.language_model
+
     def get_multimodal_embeddings(
             self, **kwargs: object) -> Optional[MultiModalEmbeddings]:
         image_input = self._parse_and_validate_image_input(**kwargs)

vllm/model_executor/models/aya_vision.py

@@ -424,6 +424,9 @@ def _parse_and_validate_image_input(
             num_patches=num_patches,
         )
 
+    def get_language_model(self) -> torch.nn.Module:
+        return self.language_model
+
     def get_multimodal_embeddings(
             self, **kwargs: object) -> Optional[MultiModalEmbeddings]:
         image_input = self._parse_and_validate_image_input(**kwargs)

vllm/model_executor/models/blip2.py

@@ -627,6 +627,9 @@ def _process_image_input(self,
 
         return self.language_projection(query_output)
 
+    def get_language_model(self) -> torch.nn.Module:
+        return self.language_model
+
     def get_multimodal_embeddings(
             self, **kwargs: object) -> Optional[MultiModalEmbeddings]:
         image_input = self._parse_and_validate_image_input(**kwargs)

vllm/model_executor/models/chameleon.py

@@ -988,6 +988,9 @@ def _parse_and_validate_image_input(
             data=self._validate_pixel_values(pixel_values),
         )
 
+    def get_language_model(self) -> torch.nn.Module:
+        return self.model
+
     def get_multimodal_embeddings(
             self, **kwargs: object) -> Optional[MultiModalEmbeddings]:
         image_input = self._parse_and_validate_image_input(**kwargs)

vllm/model_executor/models/deepseek_vl2.py

@@ -604,6 +604,9 @@ def _process_image_input(
         return self._pixel_values_to_embedding(
             pixel_values=pixel_values, images_spatial_crop=images_spatial_crop)
 
+    def get_language_model(self) -> torch.nn.Module:
+        return self.language_model
+
     def get_multimodal_embeddings(
             self, **kwargs: object) -> Optional[MultiModalEmbeddings]:
         image_input = self._parse_and_validate_image_input(**kwargs)

vllm/model_executor/models/florence2.py

@@ -1050,6 +1050,9 @@ def _process_image_input(
         pixel_values = image_input["data"]
         return self._encode_image(pixel_values)
 
+    def get_language_model(self) -> torch.nn.Module:
+        return self.language_model
+
     def get_multimodal_embeddings(
             self, **kwargs: object) -> Optional[MultiModalEmbeddings]:
         image_input = self._parse_and_validate_image_input(**kwargs)

vllm/model_executor/models/fuyu.py

@@ -341,6 +341,9 @@ def _process_image_input(
 
         return vision_embeddings_flat.split(patches_per_image, dim=0)
 
+    def get_language_model(self) -> torch.nn.Module:
+        return self.language_model
+
     def get_multimodal_embeddings(
             self, **kwargs: object) -> Optional[MultiModalEmbeddings]:
         image_input = self._parse_and_validate_image_input(**kwargs)

vllm/model_executor/models/gemma3_mm.py

@@ -591,6 +591,9 @@ def _process_image_input(
             e.flatten(0, 1) for e in image_embeds.split(num_patches.tolist())
         ]
 
+    def get_language_model(self) -> torch.nn.Module:
+        return self.language_model
+
     def get_multimodal_embeddings(
             self, **kwargs: object) -> Optional[MultiModalEmbeddings]:
         image_input = self._parse_and_validate_image_input(**kwargs)

vllm/model_executor/models/glm4v.py

@@ -596,6 +596,9 @@ def _process_image_input(
 
         return self.transformer.vision(pixel_values)
 
+    def get_language_model(self) -> torch.nn.Module:
+        return self.transformer
+
     def get_multimodal_embeddings(
             self, **kwargs: object) -> Optional[MultiModalEmbeddings]:
         image_input = self._parse_and_validate_image_input(**kwargs)