Many, but primarily, OpenAI. It's like the Beatles, one of them would have been enough, but here you have Sam Altman, Ilya Sustkever, Andrej Karpathy, Greg Brockman, among the rest of the brilliant minds there, both AI research and business. MVPs all, and all in one place.
It's completely unreal to state without specifying the market and industry. There are currently thousands of companies using LLM dev. Could you specify the industry at least?