[New Model] Devstral support (#6547)

Signed-off-by: Xinyuan Tong <justinning0323@outlook.com>

python/sglang/srt/conversation.py

@@ -21,6 +21,7 @@ from enum import IntEnum, auto
 from typing import Callable, Dict, List, Optional, Tuple, Union
 
 from sglang.srt.openai_api.protocol import ChatCompletionRequest
+from sglang.srt.utils import read_system_prompt_from_file
 
 
 class SeparatorStyle(IntEnum):
@@ -648,6 +649,20 @@ register_conv_template(
     )
 )
 
+register_conv_template(
+    Conversation(
+        name="devstral",
+        system_template="[SYSTEM_PROMPT]\n{system_message}\n[/SYSTEM_PROMPT]\n\n",
+        system_message=read_system_prompt_from_file("mistralai/Devstral-Small-2505"),
+        roles=("[INST]", "[/INST]"),
+        sep_style=SeparatorStyle.LLAMA2,
+        sep=" ",
+        sep2=" </s><s>",
+        stop_str=["[INST]", "[/INST]", "[SYSTEM_PROMPT]", "[/SYSTEM_PROMPT]"],
+        image_token="[IMG]",
+    )
+)
+
 # reference: https://huggingface.co/meta-llama/Llama-4-Scout-17B-16E-Instruct/blob/main/chat_template.json
 register_conv_template(
     Conversation(
@@ -961,6 +976,12 @@ def match_moonshot_kimivl(model_path: str):
         return "kimi-vl"
 
 
+@register_conv_template_matching_function
+def match_devstral(model_path: str):
+    if re.search(r"devstral", model_path, re.IGNORECASE):
+        return "devstral"
+
+
 @register_conv_template_matching_function
 def match_phi_4_mm(model_path: str):
     if "phi-4-multimodal" in model_path.lower():

python/sglang/srt/hf_transformers_utils.py

@@ -203,6 +203,10 @@ def get_tokenizer(
             raise ValueError("Cannot use the fast tokenizer in slow tokenizer mode.")
         kwargs["use_fast"] = False
 
+    # TODO(Xinyuan): Remove this once we have a proper tokenizer for Devstral
+    if tokenizer_name == "mistralai/Devstral-Small-2505":
+        tokenizer_name = "mistralai/Mistral-Small-3.1-24B-Instruct-2503"
+
     is_gguf = check_gguf_file(tokenizer_name)
     if is_gguf:
         kwargs["gguf_file"] = tokenizer_name

python/sglang/srt/utils.py

@@ -2169,3 +2169,51 @@ class Withable(Generic[T]):
         finally:
             assert self._value is new_value
             self._value = None
+
+
+def find_local_repo_dir(repo_id: str, revision: Optional[str] = None) -> Optional[str]:
+    import huggingface_hub as hf
+
+    # Build cache path
+    cache_path = os.path.join(
+        hf.constants.HF_HUB_CACHE,
+        hf.constants.REPO_ID_SEPARATOR.join(["models", *repo_id.split("/")]),
+    )
+
+    # Get revision from main ref if not specified
+    if not revision:
+        ref_path = os.path.join(cache_path, "refs", "main")
+        if os.path.isfile(ref_path):
+            with open(ref_path) as f:
+                revision = f.read().strip()
+
+    # List files from revision directory
+    if revision:
+        rev_dir = os.path.join(cache_path, "snapshots", revision)
+        if os.path.isdir(rev_dir):
+            return rev_dir
+
+    return None
+
+
+def read_system_prompt_from_file(model_name: str) -> str:
+    """Read system prompt from a file in the HuggingFace cache directory.
+
+    Args:
+        model_name: The model name to construct the file path
+
+    Returns:
+        The system prompt content from the file, or empty string if file not found
+    """
+    try:
+        local_repo_dir = find_local_repo_dir(model_name)
+        if local_repo_dir:
+            system_prompt_file = os.path.join(local_repo_dir, "SYSTEM_PROMPT.txt")
+            if os.path.exists(system_prompt_file):
+                with open(system_prompt_file, "r", encoding="utf-8") as f:
+                    return f.read()
+
+        return ""
+    except Exception:
+        # If anything fails, return empty string
+        return ""