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vllm - 💡(How to fix) Fix [Bug]: OpenAIServingChat silently requires new openai_serving_render kwarg since v0.18 [1 pull requests]

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Error Message

TypeError: OpenAIServingChat.init() missing 1 required keyword-only argument: 'openai_serving_render'

Fix Action

Fixed

Code Example

from vllm.engine.async_llm_engine import AsyncLLMEngine
  from vllm.engine.arg_utils import AsyncEngineArgs
  from vllm.entrypoints.openai.chat_completion.serving import OpenAIServingChat
  from vllm.entrypoints.openai.models.serving import OpenAIServingModels
  from vllm.entrypoints.openai.models.protocol import BaseModelPath

  engine = AsyncLLMEngine.from_engine_args(AsyncEngineArgs(model="Qwen/Qwen3-4B-Instruct-2507"))
  serving_models = OpenAIServingModels(
      engine_client=engine,
      base_model_paths=[BaseModelPath(name="my-model", model_path="Qwen/Qwen3-4B-Instruct-2507")],
      lora_modules=[],
  )

  OpenAIServingChat(
      engine,
      models=serving_models,
      response_role="assistant",
      request_logger=None,
      chat_template=None,
      chat_template_content_format="auto",
  )

---

TypeError: OpenAIServingChat.__init__() missing 1 required keyword-only argument: 'openai_serving_render'
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Your current environment

Since v0.18.0 (#36483), OpenAIServingChat.__init__ requires a new keyword-only argument openai_serving_render: OpenAIServingRender. This is a silent breaking change for anyone constructing OpenAIServingChat directly. We are using KubeRay + Ray Serve + FastAPI encounter this issue.

Code that worked on v0.17.0:

from vllm.engine.async_llm_engine import AsyncLLMEngine
from vllm.engine.arg_utils import AsyncEngineArgs
from vllm.entrypoints.openai.chat_completion.serving import OpenAIServingChat
from vllm.entrypoints.openai.models.serving import OpenAIServingModels
from vllm.entrypoints.openai.models.protocol import BaseModelPath

engine = AsyncLLMEngine.from_engine_args(AsyncEngineArgs(model="Qwen/Qwen3-4B-Instruct-2507"))
serving_models = OpenAIServingModels(
    engine_client=engine,
    base_model_paths=[BaseModelPath(name="my-model", model_path="Qwen/Qwen3-4B-Instruct-2507")],
    lora_modules=[],
)

OpenAIServingChat(
    engine,
    models=serving_models,
    response_role="assistant",
    request_logger=None,
    chat_template=None,
    chat_template_content_format="auto",
)

Error on v0.18.0+

TypeError: OpenAIServingChat.__init__() missing 1 required keyword-only argument: 'openai_serving_render'

Expected behavior

openai_serving_render should default to None with an internal auto-construction fallback so existing call sites keep working.

🐛 Describe the bug

N/A

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vllm - 💡(How to fix) Fix [Bug]: OpenAIServingChat silently requires new openai_serving_render kwarg since v0.18 [1 pull requests]