In one sentence
An answer engine is a system that responds to a question with a written answer rather than a list of links. ChatGPT, Google AI Overviews, Gemini, Claude, Perplexity, Copilot, Meta AI, Mistral, DeepSeek, Qwen and Kimi are the answer engines most brands need to track.
Answer engines differ in where their facts come from. Some answer mostly from model weights, some retrieve live web results before writing, and most now blend the two. That difference matters: a brand can be strong in one engine and invisible in another for reasons that have nothing to do with its website.
Because each engine has its own retrieval stack, index freshness and citation style, a single-engine check tells you very little. Coverage across engines, measured on the same prompts, is what makes the numbers comparable.