Nothing. There are no withdrawal fees from Swan. It is absolutely free!
Currently, our custody partner pays all of the miners' fees required to get a withdrawal of Bitcoin from Swan confirmed to the Bitcoin blockchain. Bitcoin miners' fees are small amounts of Bitcoin paid to whichever miner includes the transaction in the next block. They are used to incentivize Bitcoin miners to confirm transactions, and the exact amount of fees can be volatile, but the fees don't affect our customers.
If you wish to set up automatic Bitcoin withdrawals from your account (also with no fees) read here.
Most other exchanges do charge withdrawal fees. This is just another advantage you have in saving money and stacking more satoshis at Swan Bitcoin!