Constraint Decoding: Set xgrammar as the default grammar backend (#4386)

python/pyproject.toml

@@ -38,7 +38,7 @@ runtime_common = [
     "transformers==4.48.3",
     "uvicorn",
     "uvloop",
-    "xgrammar==0.1.15",
+    "xgrammar==0.1.16",
 ]
 
 srt = [

python/sglang/srt/openai_api/protocol.py

@@ -16,7 +16,7 @@
 import time
 from typing import Dict, List, Optional, Union
 
-from pydantic import BaseModel, Field
+from pydantic import BaseModel, Field, root_validator
 from typing_extensions import Literal
 
 
@@ -323,6 +323,15 @@ class ChatCompletionRequest(BaseModel):
         default="auto", examples=["none"]
     )  # noqa
 
+    @root_validator(pre=True)
+    def set_tool_choice_default(cls, values):
+        if values.get("tool_choice") is None:
+            if values.get("tools") is None:
+                values["tool_choice"] = "none"
+            else:
+                values["tool_choice"] = "auto"
+        return values
+
     # Extra parameters for SRT backend only and will be ignored by OpenAI models.
     top_k: int = -1
     min_p: float = 0.0

python/sglang/srt/server_args.py

@@ -125,7 +125,7 @@ class ServerArgs:
     # Kernel backend
     attention_backend: Optional[str] = None
     sampling_backend: Optional[str] = None
-    grammar_backend: Optional[str] = "outlines"
+    grammar_backend: Optional[str] = "xgrammar"
 
     # Speculative decoding
     speculative_algorithm: Optional[str] = None