Rubicon is an on-chain order book protocol, all transactions require network fees (gas) that are paid in ETH. Gas fees on Optimism are 50-100x cheaper than Ethereum Mainnet. You can monitor Optimism gas prices on their public dashboard.
Paid by Swaps, Market Orders, and orders that 'take' liquidity from the order book.
Maker Fee: 0.0%
Limit Orders that 'make' liquidity on the order book do not pay fees other than gas.
Liquidity Pool Fees
Withdrawal Fee: 0.03%
A withdrawal fee is paid back into the pool, effectively rewarding remaining liquidity providers. Stops pool spam.
(These are variable protocol parameters and could change)