sgl-project/sglang · error · ValueError

--enable-http2 requires the 'granian' package. Install it wi

Error message

--enable-http2 requires the 'granian' package. Install it with: pip install "sglang[http2]"

What it means

HTTP/2 serving in SGLang is backed by the granian web server, which is an optional dependency. This error is raised when --enable-http2 is used but the granian package is not installed in the environment.

Source

Thrown at python/sglang/srt/server_args.py:4358

                f"Please check the --ssl-ca-certs path."
            )
        if cfg.enable_ssl_refresh and not (cfg.ssl_certfile and cfg.ssl_keyfile):
            raise ValueError(
                "--enable-ssl-refresh requires --ssl-certfile and --ssl-keyfile "
                "to be specified."
            )

        if cfg.enable_http2:
            if not 0 < cfg.http2_max_concurrent_streams < 2**32:
                raise ValueError(
                    "--http2-max-concurrent-streams must be between 1 and "
                    "4294967295."
                )

            try:
                import granian  # noqa: F401
            except ImportError:
                raise ValueError(
                    "--enable-http2 requires the 'granian' package. "
                    'Install it with: pip install "sglang[http2]"'
                )

            if cfg.enable_ssl_refresh:
                raise ValueError(
                    "--enable-ssl-refresh is not supported with --enable-http2. "
                    "Granian does not support SSL certificate hot-reloading. "
                    "Use Uvicorn (the default) or handle certificate rotation externally."
                )

    def _handle_multimodal(self):
        """Validate mm_process_config structure before model loading."""
        cfg = resolving_view(self)
        if (
            cfg.mm_preprocess_cache_size_mb is not None
            and cfg.mm_preprocess_cache_size_mb < 0
        ):

View on GitHub (pinned to 0132848349)

Solutions

  1. Install the extra: pip install "sglang[http2]"
  2. Or install granian directly: pip install granian
  3. Or drop --enable-http2 to use the default Uvicorn HTTP/1.1 server

Example fix

# before
pip install sglang
python -m sglang.launch_server --enable-http2
# after
pip install "sglang[http2]"
python -m sglang.launch_server --enable-http2
Defensive patterns

Strategy: type-guard

Validate before calling

try:
    import granian  # noqa
except ImportError:
    raise SystemExit('pip install "sglang[http2]"')

Type guard

def has_http2_support() -> bool:
    try:
        import granian  # noqa
        return True
    except ImportError:
        return False

Prevention

When it happens

Trigger: Starting the server with --enable-http2 in an environment where 'import granian' fails (base sglang install without the http2 extra).

Common situations: Installing sglang via a minimal/base pip install or Docker image that omits extras; upgrading sglang in an old venv that predates the granian extra.

Related errors

AI-assisted analysis of sgl-project/sglang@0132848349 (2026-08-28). Data as JSON: /api/errors/8e4cda3a01427c29. Report an issue: GitHub.