Getting a new banking charter in the US is hard, but it's straightforward to be a challenger bank in the UK. Jarvis moved (back) to London from SF to start Griffin.
The banks in the US that have APIs tend to focus on large fintech partnerships, so even simple APIs will be expensive compared to a regular bank account. Grasshopper Bank in the US (for example) is one of the few that will do APIs on top of regular commercial bank accounts.
(I work at Treasury Prime, which powers many US banks that do APIs.)
The alternative everyone brings up is FedNow - slightly more expensive, but it works quickly and operates 24/7. The problem is that FedNow is a Real Time Payment system. Everyone in banking knows that Real Time payments equals Real Time Fraud.
The banks in the US that have APIs tend to focus on large fintech partnerships, so even simple APIs will be expensive compared to a regular bank account. Grasshopper Bank in the US (for example) is one of the few that will do APIs on top of regular commercial bank accounts.
(I work at Treasury Prime, which powers many US banks that do APIs.)