Microsoft Copilot is a generative artificial intelligence chatbot developed by Microsoft AI, a division of Microsoft. Based on OpenAI's GPT-4 and GPT-5 series of large language models, it was launched in 2023 as Microsoft's main replacement for the discontinued Cortana. Copilot utilizes the Microsoft Prometheus model, built upon OpenAI's GPT-4 and GPT-5 foundational large language models, which in turn have been fine-tuned using both supervised and reinforcement learning techniques.