How ChatGPT decides what to cite
ChatGPT has two distinct citation paths. In live web mode (ChatGPT search, the integrated browsing in GPT-4o and successors), it queries an underlying search index (Bing-derived plus OpenAI's own crawl), retrieves candidate URLs, and synthesizes an answer with inline citations. In training-data mode, it draws on facts learned from the open web during training and may attribute them when prompted, though attribution from training is less reliable than from live retrieval.
The citations you see in ChatGPT browsing answers are essentially a generative-engine ranking on top of a retrieval layer. The retrieval layer behaves similarly to Bing's organic index; the generative layer then chooses 3–6 sources to cite based on topical fit, extractability, and apparent credibility.