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docs/source/serving/openai_compatible_server.md

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+# OpenAI Compatible Server
+
+vLLM provides an HTTP server that implements OpenAI's [Completions](https://platform.openai.com/docs/api-reference/completions) and [Chat](https://platform.openai.com/docs/api-reference/chat) API.
+
+You can start the server using Python, or using [Docker](deploying_with_docker.rst):
+```bash
+python -m vllm.entrypoints.openai.api_server --model NousResearch/Meta-Llama-3-8B-Instruct --dtype auto --api-key token-abc123
+```
+
+To call the server, you can use the official OpenAI Python client library, or any other HTTP client.
+```python
+from openai import OpenAI
+client = OpenAI(
+    base_url="http://localhost:8000/v1",
+    api_key="token-abc123",
+)
+
+completion = client.chat.completions.create(
+  model="NousResearch/Meta-Llama-3-8B-Instruct",
+  messages=[
+    {"role": "user", "content": "Hello!"}
+  ]
+)
+
+print(completion.choices[0].message)
+```
+
+## API Reference
+Please see the [OpenAI API Reference](https://platform.openai.com/docs/api-reference) for more information on the API. We support all parameters except:
+- Chat: `tools`, and `tool_choice`.
+- Completions: `suffix`.
+
+## Extra Parameters
+vLLM supports a set of parameters that are not part of the OpenAI API.
+In order to use them, you can pass them as extra parameters in the OpenAI client.
+Or directly merge them into the JSON payload if you are using HTTP call directly.
+
+```python
+completion = client.chat.completions.create(
+  model="NousResearch/Meta-Llama-3-8B-Instruct",
+  messages=[
+    {"role": "user", "content": "Classify this sentiment: vLLM is wonderful!"}
+  ],
+  extra_body={
+    "guided_choice": ["positive", "negative"]
+  }
+)
+```
+
+### Extra Parameters for Chat API
+The following [sampling parameters (click through to see documentation)](../dev/sampling_params.rst) are supported.
+
+```{literalinclude} ../../../vllm/entrypoints/openai/protocol.py
+:language: python
+:start-after: begin-chat-completion-sampling-params
+:end-before: end-chat-completion-sampling-params
+```
+
+The following extra parameters are supported:
+
+```{literalinclude} ../../../vllm/entrypoints/openai/protocol.py
+:language: python
+:start-after: begin-chat-completion-extra-params
+:end-before: end-chat-completion-extra-params
+```
+
+### Extra Parameters for Completions API
+The following [sampling parameters (click through to see documentation)](../dev/sampling_params.rst) are supported.
+
+```{literalinclude} ../../../vllm/entrypoints/openai/protocol.py
+:language: python
+:start-after: begin-completion-sampling-params
+:end-before: end-completion-sampling-params
+```
+
+The following extra parameters are supported:
+
+```{literalinclude} ../../../vllm/entrypoints/openai/protocol.py
+:language: python
+:start-after: begin-completion-extra-params
+:end-before: end-completion-extra-params
+```
+
+## Chat Template
+
+In order for the language model to support chat protocol, vLLM requires the model to include
+a chat template in its tokenizer configuration. The chat template is a Jinja2 template that
+specifies how are roles, messages, and other chat-specific tokens are encoded in the input.
+
+An example chat template for `NousResearch/Meta-Llama-3-8B-Instruct` can be found [here](https://github.com/meta-llama/llama3?tab=readme-ov-file#instruction-tuned-models)
+
+Some models do not provide a chat template even though they are instruction/chat fine-tuned. For those model,
+you can manually specify their chat template in the `--chat-template` parameter with the file path to the chat
+template, or the template in string form. Without a chat template, the server will not be able to process chat
+and all chat requests will error.
+
+```bash
+python -m vllm.entrypoints.openai.api_server \
+  --model ... \
+  --chat-template ./path-to-chat-template.jinja
+```
+
+vLLM community provides a set of chat templates for popular models. You can find them in the examples
+directory [here](https://github.com/vllm-project/vllm/tree/main/examples/)
+
+## Command line arguments for the server
+
+```{argparse}
+:module: vllm.entrypoints.openai.cli_args
+:func: make_arg_parser
+:prog: vllm-openai-server
+```