In the past, Gemini customers had to hold GUSD in their Gemini Crypto Derivatives account to trade perpetuals. With Cross Collateral, other assets such as BTC can be used as collateral to fulfill this requirement. Cross collateral is an account level feature that customers can enable and disable independently for each of their derivative accounts depending on their trading strategy. 

In order to use cross collateral, customers can login to ActiveTrader, select the Account to Account Transfer feature from the Transfer menu, move tokens other than GUSD (for example BTC) into their derivatives account, enable Cross Collateral for that account, and start trading derivatives.

See here for tokens you can use as collateral. 

Example:

Bob holds only BTC in his Gemini account and wants to open a derivatives position to reflect his short term view on the price of PEPE. Prior to this new cross collateral feature, Bob would have only been able to use GUSD to trade derivatives on Gemini. This means he would have had to convert some of his BTC holdings into GUSD to trade PEPE perpetuals.

Now, with cross collateral, Bob has more options. He can directly deposit BTC as collateral to open a position. His use of cross collateral enabled him to do so without the need to sell some of his BTC for GUSD.

In summary, the cross collateral feature provides customers like Bob with greater flexibility and capital efficiency. Customers can now pursue trading strategies while retaining exposure to their chosen assets.