Cannot retrieve log probabilities for generated tokens

[Minh-Hoang DANG]

• This is actually a bug report.
• I am not getting good LLM Results
• I have tried asking for help in the community on discord or discussions and have not received a response.
• I have tried searching the documentation and have not found an answer.

What Model are you using?

• [x ] gpt-3.5-turbo
• gpt-4-turbo
• gpt-4
• Other (Mixtral 8x7B Instruct)

Describe the bug
I was trying to do a binary classifier that can only answer "Yes" or "No" and I also want to retrieve the log probability of the answer.
This is as simple as setting lobprobs=2 in the create_completion(). Alas, in the raw response, the logprobs field is None

To Reproduce

import enum
from typing import Literal
import httpx
from pydantic import BaseModel

from llama_cpp import Llama
from llama_cpp.llama_speculative import LlamaPromptLookupDecoding


class Labels(str, enum.Enum):
    """Enumeration for single-label text classification."""

    SPAM = "spam"
    NOT_SPAM = "not_spam"


class SinglePrediction(BaseModel):
    """
    Class for a single class label prediction.
    """

    class_label: Labels

from openai import OpenAI
import instructor

host = "localhost"
port = 8084

class Labels(str, enum.Enum):
    """Enumeration for single-label text classification."""

    SPAM = "spam"
    NOT_SPAM = "not_spam"

class BinaryPrediction(BaseModel):
    # label: Literal["TOKPOS", "TOKNEG"]
    label: Labels

# Server mode
llm = OpenAI(
    base_url=f"http://{host}:{port}/v1", api_key="sk-xxx",
    http_client=httpx.Client(
        transport=httpx.HTTPTransport(local_address="0.0.0.0"),
    ),     
)

client = instructor.patch(client=llm, mode=instructor.Mode.JSON_SCHEMA)

# Offline mode
# llm = Llama(
#     model_path=".models/models--TheBloke--Mixtral-8x7B-Instruct-v0.1-GGUF/snapshots/fa1d3835c5d45a3a74c0b68805fcdc133dba2b6a/mixtral-8x7b-instruct-v0.1.Q4_K_M.gguf", 
#     draft_model=LlamaPromptLookupDecoding(num_pred_tokens=10), # 10 is good for GPU (see https://python.useinstructor.com/hub/llama-cpp-python/#llama-cpp-python)
#     n_ctx=16385,
#     n_gpu_layers=15,
#     logits_all = True,
#     offload_kqv = True,
#     server_mode = True
# )

# client = instructor.patch(
#     create=llm.create_chat_completion_openai_v1, 
#     mode=instructor.Mode.JSON_SCHEMA
# )


def classify(data: str) -> SinglePrediction:
    """Perform single-label classification on the input text."""
 
    return client.chat.completions.create(
        model="mixtral-8x7b-instruct-v0.1",
        response_model=BinaryPrediction, 
        messages=[
            {
                "role": "user",
                "content": f"Classify the following text: {data}",
            },
        ],
        logprobs=True
    )

    # return client(
    #     response_model=BinaryPrediction, 
    #     messages=[
    #         {
    #             "role": "user",
    #             "content": f"Classify the following text: {data}",
    #         },
    #     ],
    #     logprobs=2,
    # )

# Test single-label classification
prediction = classify("Hello there I'm a Nigerian prince and I want to give you money")
print(prediction._raw_response)

$ python markup/misc/test_binary_classifier.py
ChatCompletion(id='chatcmpl-a6963005-f37d-456d-86eb-3d564616118c', choices=[Choice(finish_reason='stop', index=0, logprobs=None, message=ChatCompletionMessage(content='{ "label": "spam"}', role='assistant', function_call=None, tool_calls=None))], created=1718024981, model='gpt-3.5-turbo-16k', object='chat.completion', system_fingerprint=None, usage=CompletionUsage(completion_tokens=9, prompt_tokens=235, total_tokens=244))

Expected behavior
logprob = response._raw_response.choices[0].logprobs.content[0].logprob # expect a number