ChatGPT is an AI assistant from the US company OpenAI, released in November 2022, which brought generative AI to a broad audience. It is based on large language models from the GPT series and answers questions, writes and edits texts, summarises documents and helps with programming. ChatGPT is available in the browser and as an app, in free and paid tiers as well as versions for teams and enterprises.
OpenAI is an AI company based in San Francisco, founded in 2015 as a non-profit organisation. Since its restructuring in October 2025, it has consisted of the non-profit OpenAI Foundation, which controls the for-profit OpenAI Group PBC (as of October 2026). OpenAI is best known for ChatGPT and the GPT language models, as well as the DALL·E image generator and the Whisper speech recognition model. Its models are offered through apps and an API.
A large language model (LLM) is a neural network trained on very large amounts of text, enabling it to understand and generate language. It works by calculating the most likely next token, step by step. LLMs write, summarise, translate, answer questions and generate code; well-known examples include Claude, GPT, Gemini and Llama. Without access to current sources, they only know what was in their training data.
GPT (generative pre-trained transformer) refers to a series of large language models developed by OpenAI and based on the transformer architecture. The models are first pre-trained on vast amounts of text to predict the next token and then further trained for dialogue and following instructions. The first GPT model appeared in 2018; later generations underpin ChatGPT. In everyday speech, ‘GPT’ is often used for language models in general.
Claude is a family of large language models from the US AI company Anthropic. The models understand and write text in many languages, analyse documents, write code and can use tools, for example for research or automation. Best known are the model families Haiku, Sonnet and Opus, which differ in speed, cost and capability. Anthropic places particular emphasis on safety and reliable model behaviour.
