And probably also a lot on short fees on the securities they lend out. That depends on the actual security. Currently at Schwab it is free to short a very liq

And probably also a lot on short fees on the securities they lend out. That depends on the actual security. Currently at Schwab it is free to short a very liquid stock or ETF, because Schwab has access to a very large supply. Which means Schwab only passes along a very de minimis amount to the lender. I assume they eat this amount out of their commission. They do of course charge appropriate fees for hard-to-borrow stocks. Every stock has a different fee. This will probably change once Schwab stops charging commissions. Their fine print on that announcement says "Stock Borrow fees still apply". So those fees will apply to more/all stocks going forward?