FunctionCalling: how does 'function_call'='none' work under the API hood?

Prompting
, ,
1

I noticed that it will take one more pormpt_token when ‘function_call’ on ‘none’ than on ‘auto’

so if i set ‘funtion_call’ on ‘auto’

completion = client.chat.completions.create(
    model="gpt-3.5-turbo-0125", 
    messages=[{"role": "system", "content": ''}, 
              {"role": "user", "content": 'whats the weather in hanover'}, 
             ],
    functions=functions,
    **function_call='auto'**
)

gpt will execute the function call correctly. with 81 prompt_tokens.

"choices": [
        {
            "finish_reason": "function_call",
            "index": 0,
            "logprobs": null,
            "message": {
                "content": null,
                "function_call": {
                    "arguments": "{\"location\":\"Hanover\"}",
                    "name": "get_current_weather"
                },
                "role": "assistant"
            }
        }
    ],
"usage": {
        "completion_tokens": 16,
        "prompt_tokens": **81**,
        "total_tokens": 97
    }

and then i set it to ‘none’, model will only chat with me. and you can see it takes one more prompt_tokens than ‘auto’.

"choices": [
        {
            "finish_reason": "stop",
            "index": 0,
            "logprobs": null,
            "message": {
                "content": "Sure, let me check the current weather in Hanover for you.",
                "role": "assistant"
            }
        }
    ],
"usage": {
        "completion_tokens": 14,
        "prompt_tokens": **82**,
        "total_tokens": 96
    }

so, What is this one token under the API hood?

2

if nessary, here the function i used

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