Not nearly high-end enough. International Math Olympiad, programming olympiads, young superstars of other types, older superstars with experience, and as much diversity of genius as I can manage to pack into a very small group. The professional skills I need don't exist, and so I look for proof of relevant talent and learning rate.

I'm not sure the olympiads are such a uniquely optimal selector. For sure there were lots of superstars at the IOI, but now doing a phd makes me realise that many of those small-scale problem solving skills don't necessarily transfer to broader-scale AI research (putting together a body of work, seeing analogies between different theories, predicting which research direction will be most fruitful). Equally I met a ton of superstars working at Google, and I mean deeply brilliant superstars, not just well-trained professional coders. Google is trying to attract much the same crowd as SIAI, but they have a ton more resources, so insofar as it's possible it makes sense to try to recruit people from Google.