Codex and Copilot
OpenAI fine-tuned a language model on public code, and GitHub embedded it in the editor as an assistant completing lines as you type.
Why it matters
The first mass-market product on a large language model appeared in a code editor rather than a chat, eighteen months before ChatGPT.
Code proved a convenient testbed: it is structured, abundant in the open, and partly checkable by running it. The product immediately raised the questions that later faced the whole industry: who owns the training data, who is liable for an error, what to do about reproduced fragments of someone else's code. Lawsuits began in 2022.