Deep artificial neural networks with general-purpose language understanding and generation capabilities. Exploded in popularity after the 2017 Google paper 'Attention Is All You Need' which introduced the Transformer architecture. Strong at structuring unstructured data (paragraph → JSON/YAML), summarization, classification, language translation, content generation, and chatbot-style Q&A. Models are trained on a snapshot in time (e.g. GPT-4 through April 2023), so data becomes stale and they can hallucinate.