[CLI] Add --model-type override and keep launch_server supported (#19523)

python/sglang/cli/serve.py

@@ -10,6 +10,39 @@ from sglang.srt.utils import kill_process_tree
 logger = logging.getLogger(__name__)
 
 
+def _extract_model_type_override(extra_argv):
+    """Extract and remove --model-type override from argv."""
+    model_type = "auto"
+    filtered_argv = []
+    i = 0
+    while i < len(extra_argv):
+        arg = extra_argv[i]
+        if arg == "--model-type":
+            if i + 1 >= len(extra_argv):
+                raise Exception(
+                    "Error: --model-type requires a value. "
+                    "Valid values are: auto, llm, diffusion."
+                )
+            model_type = extra_argv[i + 1]
+            i += 2
+            continue
+
+        if arg.startswith("--model-type="):
+            model_type = arg.split("=", 1)[1]
+            i += 1
+            continue
+
+        filtered_argv.append(arg)
+        i += 1
+
+    if model_type not in ("auto", "llm", "diffusion"):
+        raise Exception(
+            f"Error: invalid --model-type '{model_type}'. "
+            "Valid values are: auto, llm, diffusion."
+        )
+    return model_type, filtered_argv
+
+
 def serve(args, extra_argv):
     if any(h in extra_argv for h in ("-h", "--help")):
         # Since the server type is determined by the model, and we don't have a model path,
@@ -22,6 +55,10 @@ def serve(args, extra_argv):
             "This command can launch either a standard language model server or a diffusion model server."
         )
         print("The server type is determined by the model path.\n")
+        print(
+            "Optional override: --model-type {auto,llm,diffusion} "
+            "(default: auto, fallback to LLM on detection failure).\n"
+        )
         print("For specific arguments, please provide a model_path.")
         print("\n--- Help for Standard Language Model Server ---")
         from sglang.srt.server_args import prepare_server_args
@@ -41,11 +78,19 @@ def serve(args, extra_argv):
         parser.print_help()
         return
 
-    model_path = get_model_path(extra_argv)
+    model_type, dispatch_argv = _extract_model_type_override(extra_argv)
+    model_path = get_model_path(dispatch_argv)
     try:
-        is_diffusion_model = get_is_diffusion_model(model_path)
-        if is_diffusion_model:
-            logger.info("Diffusion model detected")
+        if model_type == "auto":
+            is_diffusion_model = get_is_diffusion_model(model_path)
+            if is_diffusion_model:
+                logger.info("Diffusion model detected")
+        else:
+            is_diffusion_model = model_type == "diffusion"
+            logger.info(
+                "Dispatch override enabled: --model-type=%s " "(skip auto detection)",
+                model_type,
+            )
 
         if is_diffusion_model:
             # Logic for Diffusion Models
@@ -58,7 +103,7 @@ def serve(args, extra_argv):
                 description="SGLang Diffusion Model Serving"
             )
             add_multimodal_gen_serve_args(parser)
-            parsed_args, remaining_argv = parser.parse_known_args(extra_argv)
+            parsed_args, remaining_argv = parser.parse_known_args(dispatch_argv)
 
             execute_serve_cmd(parsed_args, remaining_argv)
         else:
@@ -68,7 +113,7 @@ def serve(args, extra_argv):
 
             # Add a dummy argument for the program name, expected by prepare_server_args
             # as it typically processes sys.argv
-            server_args = prepare_server_args(extra_argv)
+            server_args = prepare_server_args(dispatch_argv)
 
             run_server(server_args)
     finally: