I worked at one of the above and can confirm that the interns, particularly the R&D interns were producing truly excellent work at the forefront of their respective fields, particularly with the mentorship of the senior staff. I'm serving a 1 year non-compete at the moment, and the only thing I find myself actually missing is the internal colloquia for some of the in-house projects and research.

It's very, very cool of Jane Street to publish some of these details. All the firms are doing approximately all of the same things tech-wise, so I think Jane Street might get a leg up on the next batch of recruits just for being willing to give them some public credit.