[Feature] Add command tool parser for Command-A model #20633

gjgjos · 2025-07-08T14:51:05Z

Purpose

This PR adds a new tool parser module named CommandToolParser to support the command tool calling format used by the [CohereLabs/c4ai-command-a-03-2025](https://huggingface.co/CohereLabs/c4ai-command-a-03-2025) model.

The parser is designed to extract tool call information from model outputs that follow the <|START_ACTION|> ... <|END_ACTION|> format, parsing both synchronous and streaming responses. It leverages partial_json_parser to handle incomplete or malformed JSON in streaming scenarios gracefully.

Test Plan

Serve the model using vLLM with the following configuration:

vllm serve CohereLabs/c4ai-command-a-03-2025 \
    --enable-auto-tool-choice \
    --tool-call-parser command

Use the OpenAI-compatible API interface to send tool-calling requests:

from openai import OpenAI

client = OpenAI(
    api_key="EMPTY",
    base_url="http://localhost:8000/v1",
)

model = client.models.list().data[0].id

tools = [{
    "type": "function",
    "function": {
        "name": "get_current_weather",
        "description": "Get the current weather in a given location",
        "parameters": {
            "type": "object",
            "properties": {
                "city": {"type": "string", "description": "e.g. 'San Francisco'"},
                "state": {"type": "string", "description": "e.g. 'CA'"},
                "unit": {"type": "string", "enum": ["celsius", "fahrenheit"]}
            },
            "required": ["city", "state", "unit"]
        }
    }
}]

messages = [
    {"role": "user", "content": "Can you tell me what the temperature will be in Dallas, in fahrenheit?"}
]

response = client.chat.completions.create(
    model=model,
    messages=messages,
    tools=tools,
    temperature=0.3,
    stream=False
)

print(response)

Test Result

The model successfully produced a tool call:

{
  "tool_calls": [
    {
      "id": "chatcmpl-tool-...",
      "type": "function",
      "function": {
        "name": "get_current_weather",
        "arguments": "{\"city\": \"Dallas\", \"state\": \"TX\", \"unit\": \"fahrenheit\"}"
      }
    }
  ]
}

Accompanied by a reasoning message:

<|START_THINKING|>I will use the 'get_current_weather' tool to find out the temperature in Dallas, Texas.<|END_THINKING|>

This confirms that the command parser correctly handles tool extraction and reasoning content from the model output.

(Optional) Documentation Update

Added inline documentation within the CommandToolParser class explaining the parsing logic.
If needed, future docs can describe --tool-call-parser command as a valid option for serving command family models.

github-actions · 2025-07-08T14:51:14Z

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gemini-code-assist

Summary of Changes

Hello @gjgjos, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request integrates a new CommandToolParser to enable seamless function calling for the CohereLabs/c4ai-command-a-03-2025 model. It ensures that tool calls, which follow a specific delimited format, are correctly identified and extracted from both synchronous and streaming model outputs, thereby expanding the system's compatibility with a new family of models.

Highlights

New Tool Parser: Introduced a new CommandToolParser specifically designed to handle tool calls for the CohereLabs/c4ai-command-a-03-2025 model.
Tool Call Format Support: The parser is configured to recognize and extract tool call information enclosed within <|START_ACTION|> and <|END_ACTION|> delimiters, as used by the Command-A model.
Synchronous and Streaming Parsing: The CommandToolParser implements logic for both synchronous (batch) and streaming extraction of tool calls, ensuring compatibility with various response types.
Robust JSON Handling: It leverages partial_json_parser to gracefully handle incomplete or potentially malformed JSON payloads that may occur during streaming responses, improving parsing robustness.

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Code Review

This PR introduces a CommandToolParser for Cohere's command model tool-use format, covering both synchronous and streaming modes. A critical bug in the streaming logic leading to incorrect tool call indexing was identified and fixed, along with suggestions for improving correctness and performance.

gemini-code-assist · 2025-07-08T14:53:08Z