feat: add Crusoe managed inference backend (#20475)

Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

python/sglang/lang/backend/crusoe.py

@@ -0,0 +1,43 @@
+import os
+from typing import Optional
+
+from sglang.lang.backend.openai import OpenAI
+from sglang.lang.chat_template import ChatTemplate
+
+CRUSOE_BASE_URL = "https://managed-inference-api-proxy.crusoecloud.com/v1/"
+
+
+class Crusoe(OpenAI):
+    """SGLang backend for Crusoe managed inference.
+
+    Crusoe exposes an OpenAI-compatible API, so this is a thin wrapper
+    around the OpenAI backend that handles Crusoe-specific defaults.
+
+    Args:
+        model_name: The model to use, e.g. "meta-llama/Llama-3.1-8B-Instruct".
+        api_key: Crusoe API key. Defaults to CRUSOE_API_KEY env var.
+        base_url: Override the Crusoe endpoint. Defaults to the Crusoe API.
+        chat_template: Optional custom chat template.
+    """
+
+    def __init__(
+        self,
+        model_name: str,
+        api_key: Optional[str] = None,
+        base_url: Optional[str] = None,
+        chat_template: Optional[ChatTemplate] = None,
+        **kwargs,
+    ):
+        resolved_api_key = api_key or os.environ.get("CRUSOE_API_KEY")
+        if not resolved_api_key:
+            raise ValueError(
+                "Crusoe API key required. Pass api_key= or set CRUSOE_API_KEY."
+            )
+
+        super().__init__(
+            model_name=model_name,
+            chat_template=chat_template,
+            api_key=resolved_api_key,
+            base_url=base_url or CRUSOE_BASE_URL,
+            **kwargs,
+        )