# of employees increased a lot last few years so drawing conclusion based on that chart could be misleading.
https://www.efinancialcareers.com/news/2023/09/jane-street-jobs
I heard story that Jane st takes screening seriously (hiring cost up incuding intern training) so employee retention is good. Self claim: no kids working there.
Quant Traders are only hired from intern (there could be old intern. One year Vanessa was on camp too
https://en.wikipedia.org/wiki/Vanessa_Selbst )
Citadel is known for "easier" hiring and famous for revolving door approach. Trader 5% (10%?) lay off per quarter based on performance but those laid off people have garden leave. Good balance.