At present, the rumors about Robinhood using Arbrium to release its L2 mainly come from this tweet. Robinhood will hold a panel with Arbrium and Vitalik at ETHCC, but there is still no official statement that it will use Arbrium, which is just speculation from the outside world. This has already pushed ARB up to nearly 30%. According to Arbrium's documentation, all chains based on its issuance must be settled on Arbrium, otherwise a 10% transaction fee must be paid, while OP does not have such a requirement. Therefore, if Robinhood really chooses to use Arbrium, it is quite surprising, unless Arbrium gives Robinhood some special terms. I can't believe the reason why they don't have to choose Arbrium for their mature and free OP Stack.