Who runs it
OpenAI. It names itself with the token OAI-SearchBot.
What it does
It surfaces websites in search results in ChatGPT's search features. It is separate from GPTBot, which collects pages for training.
Renders JavaScript
Not yet observed. OpenAI doesn't say whether OAI-SearchBot runs scripts, and this site hasn't recorded a verified visit yet.
How to verify it
Match the visiting address against OpenAI's published list. OpenAI documents no reverse DNS check.
robots.txt
Rules under User-agent: OAI-SearchBot apply to it. OpenAI says sites that opt out will not be shown in ChatGPT search answers, though they can still appear as navigational links, and that changes can take about 24 hours to take effect.
Questions
Is OAI-SearchBot the same machine as GPTBot?
No. OAI-SearchBot is for search and GPTBot is for training, and each answers to its own robots.txt token.