Simplify server startup output (#20885)

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

python/sglang/cli/main.py

@@ -14,13 +14,11 @@ def main():
 
     # complex sub commands
     subparsers = parser.add_subparsers(dest="subcommand", required=True)
-
     subparsers.add_parser(
         "serve",
-        help="Launch the SGLang server.",
+        help="Launch an SGLang server.",
         add_help=False,
     )
-
     subparsers.add_parser(
         "generate",
         help="Run inference on a multimodal model.",

python/sglang/cli/serve.py

@@ -52,17 +52,13 @@ def serve(args, extra_argv):
         # we can't show the exact help. Instead, we show a general help message and then
         # the help for both possible server types.
         print(
-            "Usage: sglang serve --model-path <model-name-or-path> [additional-arguments]\n"
-        )
-        print(
-            "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(
+            "Usage: sglang serve --model-path <model-name-or-path> [additional-arguments]\n\n"
+            "This command can launch either a standard language model server or a diffusion model server.\n"
+            "The server type is determined by the --model-path.\n"
             "Optional override: --model-type {auto,llm,diffusion} "
-            "(default: auto, fallback to LLM on detection failure).\n"
+            "(default: auto, fallback to LLM on detection failure)."
         )
-        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
 
@@ -72,13 +68,22 @@ def serve(args, extra_argv):
             pass  # argparse --help calls sys.exit
 
         print("\n--- Help for Diffusion Model Server ---")
-        from sglang.multimodal_gen.runtime.entrypoints.cli.serve import (
-            add_multimodal_gen_serve_args,
-        )
+        try:
+            from sglang.multimodal_gen.runtime.entrypoints.cli.serve import (
+                add_multimodal_gen_serve_args,
+            )
 
-        parser = argparse.ArgumentParser(description="SGLang Diffusion Model Serving")
-        add_multimodal_gen_serve_args(parser)
-        parser.print_help()
+            parser = argparse.ArgumentParser(
+                prog="sglang serve",
+                description="SGLang Diffusion Model Serving",
+            )
+            add_multimodal_gen_serve_args(parser)
+            parser.print_help()
+        except ImportError:
+            print(
+                "Diffusion model support is not available. "
+                'Install with: pip install "sglang[diffusion]"'
+            )
         return
 
     model_type, dispatch_argv = _extract_model_type_override(extra_argv)

python/sglang/cli/utils.py

@@ -80,8 +80,7 @@ def get_model_path(extra_argv):
             raise Exception(
                 "Usage: sglang serve --model-path <model-name-or-path> [additional-arguments]\n\n"
                 "This command can launch either a standard language model server or a diffusion model server.\n"
-                "The server type is determined by the model path.\n"
-                "For specific arguments, please provide a model_path."
+                "The server type is determined by the --model-path.\n"
             )
         else:
             raise Exception(