Just found this on Arc’s FAQ:

we plan to make a lot of money as a company, in order to provide you (and ourselves) with the most wondrous and personal internet experience for many years to come. To do that, we’re excited about business models that align our incentives with the people who we serve: from charging companies that want to increase the productivity of their teams across the many tools they use for work, to making it easier and safer to pay for things online.