The secret sauce is spending millions on collecting a great human curated dataset and scaling up training as much as possible.
It's no secret. OpenAI isn't the only player in the field. The whole world has seen the power of Generative Pre-Trained Transformers and many organizations and even governments are going to develop and fine-tune their own custom LLMs. Of course it demands huge amount of training data and computing power but that's no secret.
It's all stone soup. Everyone chucked something into the pot. Now it's an eldrich horror that they attempt to steer with evals and system prompts.