How to finetune gpt-3.5-turbo

How to finetune gpt-3.5-turbo

Exciting news from OpenAI: you can now fine-tune your GPT-3.5-turbo models. Early testers have seen performance on narrow tasks surpassing GPT-4 at a fraction of the cost and with much faster response times. This is because they're working with a model that they have fine-tuned to meet the needs of their specific application.

There are four steps to fine-tune your OpenAI model:

  1. Prepare your data.
  2. Upload your data.
  3. Train your model
  4. Use your model

In the rest of this post we'll fine-tune and train gpt 3.5-turbo. If you'd prefer video to text, you can watch the six minute video tutorial on fine-tuning gpt 3.5 turbo.

Why fine-tune GPT 3.5-Turbo?

OpenAI mentioned three use cases in their fine-tuning announcement blog post:

  1. Improved steerability. You have more control over a model that you've fine tuned on your own data.
  2. More reliable output formatting. For instance, ensuring that generated data matches a specific json format.
  3. Custom tone. Brands have custom tones, authors have their own tone. If you fine tune a model on content that you've written, it's more likely that the the output will match your tone.

Let's focus on this third use case and fine-tune a model to generate text in a custom tone. For a sample project, we need data that is not copyrighted, easily available, and has a distinctive tone so we know if it's working. In the video I used Proverbs from the Old Testament, but you may be sitting on your own proprietary data.

Prepare your fine-tuning data

The format we're looking for is jsonl (or json-lines) – a format where each line in the file contains a separate JSON object. In our case each line represents a system message, a user message, and a sample desired response from the assistant.

Here's a sample from the OpenAI docs on fine-tuning.

{"messages": [{"role": "system", "content": "Marv is a factual chatbot that is also sarcastic."}, {"role": "user", "content": "What's the capital of France?"}, {"role": "assistant", "content": "Paris, as if everyone doesn't know that already."}]}
{"messages": [{"role": "system", "content": "Marv is a factual chatbot that is also sarcastic."}, {"role": "user", "content": "Who wrote 'Romeo and Juliet'?"}, {"role": "assistant", "content": "Oh, just some guy named William Shakespeare. Ever heard of him?"}]}
{"messages": [{"role": "system", "content": "Marv is a factual chatbot that is also sarcastic."}, {"role": "user", "content": "How far is the Moon from Earth?"}, {"role": "assistant", "content": "Around 384,400 kilometers. Give or take a few, like that really matters."}]}

The easiest way to convert text to json-l is to use ChatGPT Code Interpreter (you'll need the $20 ChatGPT Plus subscription.) It took ten minutes of chatting with the code interpreter to convert the raw text of Proverbs into the format above.


The full dataset comes out to ~700 records, but I pared this down to 18 for testing. You need a minimum of ten records for fine-tuning, and the time to train your model scales with the number of records.

Upload Fine-Tuning Data

Use the OpenAI Python library:

import openai

response = openai.File.create(
  file=open("YOURFILENAME.jsonl", "rb"),


A sample response looks like:

  "object": "file",
  "id": "file-kTPxsdHNFhT755CFyFkV68Pi",
  "purpose": "fine-tune",
  "filename": "file",
  "bytes": 8385,
  "created_at": 1692801844,
  "status": "uploaded",
  "status_details": null

You'll need that file id for the next step.

Train your model

Create a new fine tuning job using your file id from step 2:

import os
import openai
openai.api_key = os.getenv("OPENAI_API_KEY")
file_id = "file-yRdnc3zfVwTbvrn0pQ2dsN9I"
response = openai.FineTuningJob.create(training_file=file_id, 

Here's a sample response:

  "object": "fine_tuning.job",
  "id": "ftjob-eLvEAv6VEzXllDvPE9Qk45kz",
  "model": "gpt-3.5-turbo-0613",
  "created_at": 1692801986,
  "finished_at": null,
  "fine_tuned_model": null,
  "organization_id": "org-sRhvEIyDb8hsq6q04MPW5ViJ",
  "result_files": [],
  "status": "created",
  "validation_file": null,
  "training_file": "file-yRdnc3zfVwTbvrn0pQ2dsN9I",
  "hyperparameters": {
    "n_epochs": 5
  "trained_tokens": null

Very importantly: this script merely starts the training job. You will get an email when the job is completed a name for your new model. For the sake of expectation setting: fine-tuning with a minimal set of 18 rows was taking 15+ minutes on the first day fine-tuning was released. But, eventually, you'll get an email that looks like this:

Use your fine-tuned model

I use Langchain – a framework for building LLM powered apps – for most of my LLM development. To use your fine-tune model, simply change the model name to the one sent to you via email:

from langchain.chat_models import ChatOpenAI
from langchain.schema import HumanMessage

model_name = "ft:gpt-3.5-turbo-0613:personal::7qZjgwWl"
chat = ChatOpenAI(model=model_name)

messages = [
    HumanMessage(content="What is the meaning of life?")

response = chat(messages)

And that's it! You now have a fine-tuned gpt 3.5 turbo model.

If you want to see gpt fine-tuning in action, watch this six minute video tutorial.