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

> Source: https://sukruyusufkaya.com/learn/fine-tuning-cookbook/ftc-openai-fine-tuning-api
> Updated: 2026-08-15T22:38:51.622Z
> Category: Fine-Tuning Cookbook (Model-by-Model)
> Module: Part XIV — Closed-Source API Fine-Tuning
**TLDR:** OpenAI fine-tuning API'sinin tam pratiği: JSONL format (chat messages), validation set, hyperparameter override (epochs/lr/batch), upload/monitor/download checkpoint flow. Cost telemetry: training token × $25/M (GPT-4o-mini), inference 1.5× base price. RTX 4090'da kendi 1000 TR örneğin GPT-4o-mini'yi 30 dakikada FT eder.