AI companies send bots to websites for three reasons: to collect training data (GPTBot, ClaudeBot, CCBot), to build a search index (OAI-SearchBot, PerplexityBot) and to answer a live question from a user (ChatGPT-User, Claude-User, Perplexity-User).
The last kind matters most: it means someone just asked an assistant something and your page was read to answer it.
This is a test site run by 3RD (get3rd.com) to check how AI agents visit websites.