OpenRouter's web-search option changes a request by adding retrieved web results to the prompt before the model answers. In its January 2025 announcement, the service passes the user's prompt to the search provider Exa, which runs searches and summarizes the results. Those results are merged into a system message placed ahead of the user's message, with default instructions to cite sources as links. Developers switch this on with the web plugin or by appending :online to a model name, and can change the number of results (five by default) and replace the instruction text. The model is not modified: it answers from input that now includes search results.
