[Fix] Add speculative_draft_model_revision to server_args (#5255)

Signed-off-by: Devashish Lal <devashish@rivosinc.com>

python/sglang/srt/server_args.py

@@ -249,6 +249,7 @@ class ServerArgs:
     # Speculative decoding
     speculative_algorithm: Optional[str] = None
     speculative_draft_model_path: Optional[str] = None
+    speculative_draft_model_revision: Optional[str] = None
     speculative_num_steps: Optional[int] = None
     speculative_eagle_topk: Optional[int] = None
     speculative_num_draft_tokens: Optional[int] = None
@@ -1498,6 +1499,14 @@ class ServerArgs:
             type=str,
             help="The path of the draft model weights. This can be a local folder or a Hugging Face repo ID.",
         )
+        parser.add_argument(
+            "--speculative-draft-model-revision",
+            type=str,
+            default=None,
+            help="The specific draft model version to use. It can be a branch "
+            "name, a tag name, or a commit id. If unspecified, will use "
+            "the default version.",
+        )
         parser.add_argument(
             "--speculative-num-steps",
             type=int,