[Model] Remove hardcoded image tokens ids from Pixtral (#11582)

Signed-off-by: Roger Wang <ywang@roblox.com>

vllm/model_executor/models/pixtral.py

@@ -45,13 +45,6 @@ try:
 except ImportError:
     USE_XFORMERS_OPS = False
 
-# These token ids cannot be retrieved from model config
-# so we hardcode them here.
-PIXTRAL_12B_IMAGE_BREAK_ID = 12
-PIXTRAL_12B_IMAGE_END_ID = 13
-PIXTRAL_LARGE_IMAGE_BREAK_ID = 14
-PIXTRAL_LARGE_IMAGE_END_ID = 15
-
 
 def get_max_pixtral_image_tokens(ctx: InputContext):
     tokenizer = cached_get_tokenizer(
@@ -201,6 +194,13 @@ class PixtralForConditionalGeneration(nn.Module, SupportsMultiModal,
             if key in dataclass_fields
         }
 
+        if not ("image_break_token_id" in vision_args
+                and "image_end_token_id" in vision_args):
+            raise ValueError(
+                "'image_break_token_id' and 'image_end_token_id' not found "
+                "in the vision_encoder arguments. Please download the latest "
+                "version of 'params.json' from the model repository.")
+
         self.vision_args = VisionEncoderArgs(**vision_args)
 
         # init MistralForCausalLM
@@ -240,9 +240,8 @@ class PixtralForConditionalGeneration(nn.Module, SupportsMultiModal,
 
         # NOTE: Image embeddings are split into separate tensors for each image
         # by the indices of `[IMG_END]` token.
-        image_end_condition = (image_tokens == PIXTRAL_12B_IMAGE_END_ID) | (
-            image_tokens == PIXTRAL_LARGE_IMAGE_END_ID)
-        split_indices = torch.where(image_end_condition)[0] + 1
+        image_end_mask = image_tokens == self.vision_args.image_end_token_id
+        split_indices = torch.where(image_end_mask)[0] + 1
         if len(split_indices) <= 1:
             # Do not split, return as tensor of shape [1, fs, hs]
             return image_embeds.unsqueeze(0)
@@ -265,10 +264,8 @@ class PixtralForConditionalGeneration(nn.Module, SupportsMultiModal,
             inputs_embeds = merge_multimodal_embeddings(
                 input_ids, inputs_embeds, multimodal_embeddings, [
                     self.vision_args.image_token_id,
-                    PIXTRAL_12B_IMAGE_END_ID,
-                    PIXTRAL_12B_IMAGE_BREAK_ID,
-                    PIXTRAL_LARGE_IMAGE_BREAK_ID,
-                    PIXTRAL_LARGE_IMAGE_END_ID,
+                    self.vision_args.image_break_token_id,
+                    self.vision_args.image_end_token_id,
                 ])
         return inputs_embeds
 
@@ -409,6 +406,8 @@ class VisionEncoderArgs:
     num_attention_heads: int
     rope_theta: float  # for rope-2D
     image_token_id: int
+    image_break_token_id: int
+    image_end_token_id: int
     adapter_bias: bool = True