The Hop DAO received 1m $OP tokens as part of the initial Optimism airdrops to projects building early on Optimism.
These funds have been allocated to an on-boarding scheme where users receive 80% of the bridge fees paid back to them in $OP tokens almost completely removing the friction to bridge into Optimism and making Hop the cheapest route to bridge into Optimism.
The amount is based on a fixed percentage of the source transaction fee (based on gas cost on Ethereum) + Bonder fee + AMM fee. Moreover, it's capped at 20 $OP per transfer.
The rewards can be collected in the "rewards" section of the Hop home page.
"Claimable" rewards are all $OP that you can claim immediately.
"Pending" rewards are all $OP that you’ll be able to claim once the merkle root is published for the week.
There’s no rush to claim your “claimable” rewards. Rewards continue to add up as you do new transfers on Hop so it’s completely up to you when you want to claim.