Here's another article on this:
Bitcoin in the proprietary DAA will be held in the Fidelity Digital Assets custody platform in a measure meant to provide institutional-grade security.
MicroStrategy To Allow Employees To Invest In Bitcoin As Part Of 401(k) Plan https://bitcoinmagazine.com/business/microstrategy-to-allow-employees-to-invest-in-bitcoin-as-part-of-401k-plan