Transformers responses API (#1)

README.md

@@ -273,6 +273,7 @@ You can start this server with the following inference backends:
 - `metal` — uses the metal implementation on Apple Silicon only
 - `ollama` — uses the Ollama /api/generate API as a inference solution
 - `vllm` — uses your installed vllm version to perform inference
+- `transformers` — uses your installed transformers version to perform local inference
 
 ```bash
 usage: python -m gpt_oss.responses_api.serve [-h] [--checkpoint FILE] [--port PORT] [--inference-backend BACKEND]

gpt_oss/responses_api/inference/transformers.py

@@ -0,0 +1,56 @@
+"""
+NOTE: this is not the most efficient way to use transformers. It's a simple implementation that infers
+one token at a time to mimic the behavior of the Triton implementation.
+"""
+
+import os
+from typing import Callable, List
+
+# Transformers imports
+from transformers import AutoModelForCausalLM, PreTrainedModel
+import torch
+
+
+DEFAULT_TEMPERATURE = 0.0
+TP = os.environ.get("TP", 2)
+
+def load_model(checkpoint: str):
+    """
+    Serve the model directly with the Auto API.
+    """
+
+    model = AutoModelForCausalLM.from_pretrained(
+        checkpoint,
+        torch_dtype=torch.bfloat16,
+        device_map="auto",
+    )
+
+    return model
+
+
+def get_infer_next_token(model: PreTrainedModel):
+    """
+    Return a callable with the same shape as the original triton implementation:
+      infer_next_token(tokens: List[int], temperature: float, new_request: bool) -> int
+
+    Implementation detail:
+      - We issue a single-token generation with using model.generate
+      - generate handles sampling (temperature=0 => greedy, otherwise, sampling).
+    """
+
+    def infer_next_token(
+        tokens: List[int],
+        temperature: float = DEFAULT_TEMPERATURE,
+        new_request: bool = False, # kept for interface compatibility; unused here
+    ) -> int:
+        tokens = torch.tensor([tokens], dtype=torch.int64, device=model.device)
+        output = model.generate(tokens, max_new_tokens=1, do_sample=temperature != 0, temperature=temperature)
+        return output[0, -1].tolist()
+
+    return infer_next_token
+
+
+def setup_model(checkpoint: str) -> Callable[[List[int], float, bool], int]:
+    model = load_model(checkpoint)
+    infer_next_token = get_infer_next_token(model)
+    return infer_next_token

gpt_oss/responses_api/serve.py

@@ -47,6 +47,8 @@ if __name__ == "__main__":
         from .inference.ollama import setup_model
     elif args.inference_backend == "vllm":
         from .inference.vllm import setup_model
+    elif args.inference_backend == "transformers":
+        from .inference.transformers import setup_model
     else:
         raise ValueError(f"Invalid inference backend: {args.inference_backend}")