How Perplexity selects sources
Perplexity uses a hybrid retrieval system: its own crawler (PerplexityBot, user-agent visible in server logs), partner search indexes, and direct integrations with academic and reference databases. For a given query, it retrieves a candidate set of URLs, scores them on relevance and source quality, and feeds the top set into the answer-generation step. The cited sources you see in the UI are the subset the generation step actually drew from.
Perplexity's source preference skews more academic and reference-oriented than ChatGPT or Claude. On many factual queries it disproportionately cites peer-reviewed papers, government data, Wikipedia, and official documentation, with editorial and specialist sites filling in for queries where primary sources are sparse.