OpenAI officially launched ChatGPT to the public on November 30, 2022, bringing conversational artificial intelligence to audiences worldwide. The system hit 100 million active users within just two months, breaking records set by major consumer tech companies. After funding rounds in 2019 and 2021, Microsoft boosted its support with a multibillion-dollar investment announced in January 2023. Modern language models trace their roots back to a 2017 Google paper titled “Attention Is All You Need,” which introduced the transformer architecture. OpenAI’s developers created Generative Pre-trained Transformers, or GPT models, which analyze massive texts to predict the next tokens using statistical patterns. A neural network’s basic unit is a neuron or node; when thousands or millions of these nodes connect through several hidden layers—often more than three between input and output—the system achieves deep learning. The main training algorithm is backpropagation, which became widely known for multi-layer networks in a 1986 paper by Rumelhart, Hinton, and Williams. OpenAI has not officially disclosed the exact parameter counts for GPT-4 as of July 2026.