GPT-4, or Generative Pre-trained Transformer 4, is a large multimodal language model created by OpenAI, and the fourth in the GPT series. It is a significant advancement over previous models such as GPT-3, with improvements in model size, performance, contextual understanding, and safety. GPT-4 uses a Transformer architecture, a deep learning model that has revolutionized natural language processing. It can process both text and images, and it has a larger context window than GPT-3, enabling it to handle longer documents and more complex tasks. GPT-4 was trained using a combination of publicly available data and licensed third-party data, and then fine-tuned using reinforcement learning and human feedback. It also has increased reasoning and generalization abilities, making it more reliable for advanced and specialized applications.