Hence the big push currently ongoing to allow 401ks to invest in private markets
The economic vampires must salivate about this opportunity all night and day.
It's mostly known, but you're probably right it's not exactly known
45 trillion across all retirement accounts, 12 trillion in defined contribution (including 401k), 9 trillion in just 401k
https://www.ici.org/statistical-report/ret_25_q2
In that chart, the 18T of IRA has portion in private equity, and the 15T of pension (defined benefit) has a portion in private equity. The 13T defined contribution plans (of which the vast majority is 401k) can't be placed in private equity right now.