# OpenAI GPT-4o-mini / GPT-4o / GPT-4.1 Fine-Tuning API: JSONL Schema + Cost + Dashboard

> Source: https://sukruyusufkaya.com/en/learn/fine-tuning-cookbook/ftc-openai-fine-tuning-api
> Updated: 2026-05-14T14:42:59.993Z
> Category: Fine-Tuning Cookbook (Model-by-Model)
> Module: Part XIV — Closed-Source API Fine-Tuning
**TLDR:** Full practice of OpenAI fine-tuning API: JSONL format (chat messages), validation set, hyperparameter override, upload/monitor/download flow. Cost telemetry: training tokens × $25/M (GPT-4o-mini), inference 1.5× base. Your 1000 TR examples fine-tune GPT-4o-mini in 30 min.