diff --git a/src/utils/vllm_backend_utils.py b/src/utils/vllm_backend_utils.py
index c7596d6d..2c6cd5b9 100644
--- a/src/utils/vllm_backend_utils.py
+++ b/src/utils/vllm_backend_utils.py
@@ -27,7 +27,12 @@
 import json
 from collections.abc import AsyncIterator
 from contextlib import asynccontextmanager
-from typing import Optional
+from typing import Optional, Union
+
+try:
+    from interegular.patterns import parse_pattern
+except ImportError:
+    parse_pattern = None
 
 from vllm.engine.arg_utils import AsyncEngineArgs
 from vllm.engine.protocol import EngineClient
@@ -89,10 +94,33 @@ def from_dict(
                 str: str,
                 Optional[int]: int,
             }
-            for key, value in params_dict.items():
+            
+            # Remove None values to let vLLM use defaults
+            params_dict = {k: v for k, v in params_dict.items() if v is not None}
+
+            for key, value in list(params_dict.items()):
                 if key == "structured_outputs":
                     params_dict[key] = StructuredOutputsParams(**json.loads(value))
-                elif key in vllm_params_dict:
+                elif key == "guided_decoding":
+                    if isinstance(value, str):
+                        value = json.loads(value)
+                    
+                    # Map guided_decoding to structured_outputs
+                    # Remove backend if present as it is not supported in StructuredOutputsParams constructor
+                    if "backend" in value:
+                        backend = value.pop("backend")
+                        if backend not in ["xgrammar", "xgrammar:no-fallback", "auto", "xgrammar:_auto"]:
+                             raise ValueError(f"guided_decoding.backend is no longer supported request-level. Provided: {backend}")
+                    
+                    # If structured_outputs is not already set, use guided_decoding params
+                    if "structured_outputs" not in params_dict:
+                        params_dict["structured_outputs"] = StructuredOutputsParams(**value)
+                    
+            if "guided_decoding" in params_dict:
+                del params_dict["guided_decoding"]
+
+            for key, value in params_dict.items():
+                if key in vllm_params_dict:
                     vllm_type = vllm_params_dict[key]
                     if vllm_type in type_mapping:
                         params_dict[key] = type_mapping[vllm_type](params_dict[key])
@@ -105,6 +133,74 @@ def from_dict(
             )
             return None
 
+    def __post_init__(self):
+        super().__post_init__()
+
+        # Validate the structured outputs parameters.
+        if self.structured_outputs:
+            if not isinstance(self.structured_outputs, StructuredOutputsParams):
+                raise ValueError(
+                    "structured_outputs must be of type StructuredOutputsParams"
+                )
+            TritonSamplingParams._validate_guided_params(self.structured_outputs)
+
+    @staticmethod
+    def _validate_guided_params(params: StructuredOutputsParams):
+        """
+        Validates the structured outputs parameters.
+        Raises an exception if the parameters are invalid.
+        """
+        if not params:
+            return
+
+        if not isinstance(params, StructuredOutputsParams):
+            raise ValueError("structured_outputs must be of type StructuredOutputsParams")
+
+        # Validate regex constraint if provided.
+        if params.regex:
+            if not isinstance(params.regex, str):
+                raise ValueError("structured_outputs.regex must be a string")
+            if parse_pattern:
+                try:
+                    parse_pattern(params.regex)
+                except Exception as e:
+                    raise ValueError(f"Invalid regex constraint: {e}") from e
+            
+        # backend validation is removed as it is not exposed in StructuredOutputsParams
+        # and handled during construction/mapping.
+
+        if params.grammar:
+            if not isinstance(params.grammar, str):
+                raise ValueError("grammar must be a string, describing a BNF grammar")
+           
+            try:
+                from xgrammar import \
+                    Grammar  # type: ignore[import]: do NOT move up to avoid premature CUDA init
+
+                # Try to parse the converted grammar, to fail this request early
+                Grammar.from_ebnf(params.grammar)
+            except ImportError:
+                pass
+            except RuntimeError as e:
+                raise ValueError(f"Invalid BNF grammar: {e}") from e
+
+        # Validate choice constraint.
+        if params.choice:
+            if not isinstance(params.choice, list):
+                raise ValueError("choice must be a list")
+            for item in params.choice:
+                if not isinstance(item, str):
+                    raise ValueError("Each element in choice must be a string")
+
+        # Validate JSON constraint.
+        if params.json:
+            if not isinstance(params.json, dict):
+                raise ValueError("json must be a JSON schema dictionary")
+
+        # Validate whitespace_pattern constraint.
+        if params.whitespace_pattern:
+            if not isinstance(params.whitespace_pattern, str):
+                raise ValueError("whitespace_pattern must be a string")
 
 # Copy from vllm/vllm/entrypoints/openai/api_server.py with custom stat_loggers
 @asynccontextmanager