[Core]: Remove V1 engine proxy as no longer required

[hickeyma]

As V1 is now default engine, there is not longer a need to set class proxy for V1 to V0 engine.

Related #18571

Local testing shown below.

$ cat simple_test_vllm.py

from vllm import LLM, SamplingParams

def main():
    prompts = [
        "Hello, my name is",
        "The president of the United States is",
        "The capital of France is",
        "The future of AI is",
    ]
    sampling_params = SamplingParams(temperature=0.8, top_p=0.95)
    model = "meta-llama/Meta-Llama-3.1-8B-Instruct"

    llm = LLM(model=model)

    outputs = llm.generate(prompts, sampling_params)

    for output in outputs:
        prompt = output.prompt
        generated_text = output.outputs[0].text
        print(f"Prompt: {prompt!r}, Generated text: {generated_text!r}")

if __name__ == "__main__":
    main()(vllm)

$ python simple_test_vllm.py 

NFO 08-27 16:06:36 [__init__.py:241] Automatically detected platform cuda.
INFO 08-27 16:06:37 [utils.py:326] non-default args: {'model': 'meta-llama/Meta-Llama-3.1-8B-Instruct', 'disable_log_stats': True}
INFO 08-27 16:06:56 [__init__.py:742] Resolved architecture: LlamaForCausalLM
INFO 08-27 16:06:56 [__init__.py:1786] Using max model len 131072
INFO 08-27 16:07:00 [scheduler.py:222] Chunked prefill is enabled with max_num_batched_tokens=8192.
(EngineCore_0 pid=231141) INFO 08-27 16:07:06 [core.py:644] Waiting for init message from front-end.
(EngineCore_0 pid=231141) INFO 08-27 16:07:06 [core.py:74] Initializing a V1 LLM engine (v0.10.1rc2.dev249+g1fdc73241.d20250827) with config: model='meta-llama/Meta-Llama-3.1-8B-Instru
[...]
Processed prompts: 100%|███████████████████████████████████████████████████████████████████████████| 4/4 [00:00<00:00,  9.80it/s, est. speed input: 63.69 toks/s, output: 156.78 toks/s]
Prompt: 'Hello, my name is', Generated text: ' Helen and I am a devoted animal lover and owner of Angels of Mercy. I'
Prompt: 'The president of the United States is', Generated text: ' trying to convince the American public that he is not a threat to global security.\n'
Prompt: 'The capital of France is', Generated text: ' Paris, a city that has captured the hearts of millions of tourists from all over'
Prompt: 'The future of AI is', Generated text: ' exciting, but also raises questions about the role of humans in this new world.'

$ VLLM_USE_V1=1 python simple_test_vllm.py 

INFO 08-27 16:10:25 [__init__.py:241] Automatically detected platform cuda.
INFO 08-27 16:10:26 [utils.py:326] non-default args: {'model': 'meta-llama/Meta-Llama-3.1-8B-Instruct', 'disable_log_stats': True}
INFO 08-27 16:10:40 [__init__.py:742] Resolved architecture: LlamaForCausalLM
INFO 08-27 16:10:40 [__init__.py:1786] Using max model len 131072
INFO 08-27 16:10:42 [scheduler.py:222] Chunked prefill is enabled with max_num_batched_tokens=8192.
(EngineCore_0 pid=231435) INFO 08-27 16:10:45 [core.py:644] Waiting for init message from front-end.
(EngineCore_0 pid=231435) INFO 08-27 16:10:45 [core.py:74] Initializing a V1 LLM engine (v0.10.1rc2.dev249+g1fdc73241.d20250827) with config: model='meta-llama/Meta-Llama-3.1-8B-Instruct'
[...]
Processed prompts: 100%|███████████████████████████████████████████████████████████████████████████| 4/4 [00:00<00:00,  9.79it/s, est. speed input: 63.64 toks/s, output: 156.66 toks/s]
Prompt: 'Hello, my name is', Generated text: ' Helen and I am a devoted animal lover and owner of Angels of Mercy. I'
Prompt: 'The president of the United States is', Generated text: ' trying to convince the American public that he is not a threat to global security.\n'
Prompt: 'The capital of France is', Generated text: ' Paris, a city that has captured the hearts of millions of tourists from all over'
Prompt: 'The future of AI is', Generated text: ' exciting, but also raises questions about the role of humans in this new world.'

$ VLLM_USE_V1=0 python simple_test_vllm.py 

NFO 08-27 16:21:22 [__init__.py:241] Automatically detected platform cuda.
INFO 08-27 16:21:23 [utils.py:326] non-default args: {'model': 'meta-llama/Meta-Llama-3.1-8B-Instruct', 'disable_log_stats': True}
INFO 08-27 16:21:36 [__init__.py:742] Resolved architecture: LlamaForCausalLM
INFO 08-27 16:21:36 [__init__.py:1786] Using max model len 131072
WARNING 08-27 16:21:36 [arg_utils.py:1578] Chunked prefill is enabled by default for models with max_model_len > 32K. Chunked prefill might not work with some features or models. If you encounter any issues, please disable by launching with --enable-chunked-prefill=False.
INFO 08-27 16:21:39 [scheduler.py:222] Chunked prefill is enabled with max_num_batched_tokens=2048.
INFO 08-27 16:21:39 [llm_engine.py:222] Initializing a V0 LLM engine (v0.10.1rc2.dev249+g1fdc73241.d20250827) with config: model='meta-llama/Meta-Llama-3.1-8B-Instruct'
[...]
Processed prompts: 100%|███████████████████████████████████████████████████████████████████████████| 4/4 [00:00<00:00,  9.48it/s, est. speed input: 61.64 toks/s, output: 151.74 toks/s]
Prompt: 'Hello, my name is', Generated text: ' Rob Thomas and I am a highly experienced and skilled Acoustic Guitarist. I'
Prompt: 'The president of the United States is', Generated text: ' the most powerful person in the world. The president is both the head of state'
Prompt: 'The capital of France is', Generated text: ' a popular destination for tourists. It is a city with rich history, art,'
Prompt: 'The future of AI is', Generated text: ' being shaped by the work of researchers like Victor Zhang, a computer science Ph.D'

$ python -m vllm.entrypoints.api_server --model "meta-llama/Meta-Llama-3.1-8B-Instruct"

INFO 08-28 08:41:57 [__init__.py:241] Automatically detected platform cuda.
INFO 08-28 08:41:58 [api_server.py:122] vLLM API server version 0.10.1rc2.dev310+g4f35be10a
[...]
(EngineCore_0 pid=259025) INFO 08-28 08:42:17 [core.py:75] Initializing a V1 LLM engine (v0.10.1rc2.dev310+g4f35be10a) with config: model='meta-llama/Meta-Llama-3.1-8B-Instruct', 
[...]
INFO:     127.0.0.1:50376 - "POST /generate HTTP/1.1" 200 OK

$ python https://github.com/vllm-project/vllm/blob/main/examples/online_serving/api_client.py

Prompt: 'San Francisco is a'

Beam candidate 0: 'San Francisco is a top tourist destination, and for good reason. The city is known for its iconic'

$ VLLM_USE_V1=1 python -m vllm.entrypoints.api_server --model "meta-llama/Meta-Llama-3.1-8B-Instruct"
INFO 08-28 09:02:53 [__init__.py:241] Automatically detected platform cuda.
INFO 08-28 09:02:54 [api_server.py:122] vLLM API server version 0.10.1rc2.dev310+g4f35be10a
[...]
(EngineCore_0 pid=259753) INFO 08-28 09:03:13 [core.py:75] Initializing a V1 LLM engine (v0.10.1rc2.dev310+g4f35be10a) with config: model='meta-llama/Meta-Llama-3.1-8B-Instruct',
[...]
INFO:     127.0.0.1:36952 - "POST /generate HTTP/1.1" 200 OK

$ python https://github.com/vllm-project/vllm/blob/main/examples/online_serving/api_client.py

Prompt: 'San Francisco is a'

Beam candidate 0: 'San Francisco is a top tourist destination, and for good reason. The city is known for its iconic'

$ VLLM_USE_V1=0 python -m vllm.entrypoints.api_server --model "meta-llama/Meta-Llama-3.1-8B-Instruct"

INFO 08-28 09:06:25 [__init__.py:241] Automatically detected platform cuda.
INFO 08-28 09:06:26 [api_server.py:122] vLLM API server version 0.10.1rc2.dev310+g4f35be10a
[...]
INFO 08-28 09:06:41 [llm_engine.py:223] Initializing a V0 LLM engine (v0.10.1rc2.dev310+g4f35be10a) with config: model='meta-llama/Meta-Llama-3.1-8B-Instruct', speculative_config=None, tokenizer='meta-llama/Meta-Llama-3.1-8B-Instruct', skip_tokenizer_init=False, tokenizer_mode=auto, revision=None, override_neuron_config={}, tokenizer_revision=None, 
[...]
INFO:     127.0.0.1:36952 - "POST /generate HTTP/1.1" 200 OK

$ python https://github.com/vllm-project/vllm/blob/main/examples/online_serving/api_client.py

Prompt: 'San Francisco is a'

Beam candidate 0: 'San Francisco is a top tourist destination, and for good reason. The city is known for its iconic'

[gemini-code-assist]

Code Review

This pull request removes the module-level class proxies that conditionally switched to the V1 engine. This is a good cleanup step that aligns with making the V1 engine the default. My review includes suggestions to remove other now-redundant conditional logic related to the VLLM_USE_V1 flag to fully complete this refactoring and improve code maintainability.

[robertgshaw2-redhat]

this is not ready yet. users can still opt into V0 so this is still needed. Once V0 is compeltely removed we can get rid of this

[hickeyma]

this is not ready yet. users can still opt into V0 so this is still needed. Once V0 is compeltely removed we can get rid of this

@robertgshaw2-redhat Ok but can't users still use v0 as shown in the output in the description (VLLM_USE_V1=0)? Or what use case do you mean?

[robertgshaw2-redhat]

what is inside simple_test_vllm.py? this override is for users direclty importing AsyncLLM

[hickeyma]

what is inside simple_test_vllm.py? this override is for users direclty importing AsyncLLM

@robertgshaw2-redhat I updated the testing info in description (showing simple test from quickstart which is synchronous).

I also tested with https://github.com/vllm-project/vllm/blob/main/examples/online_serving/api_client.py which connects to vLLM API server. This tests using AsyncLLM if I understand it correctly?

[hickeyma]

Closing as superseded by #25025