It's a YC company, they get special treatment, e.g. spot on the frontend. Of course they would post. <a href="https://news.ycombinator.com/newsfaq.html" rel="nofollow">https://news.ycombinator.com/newsfaq.html</a> (in the "Can I post a job ad" section). Given the hundreds of YC companies I wonder more why there aren't ads all the time.