Every state is different. In California electric bicycles are class 1, 2 and 3, with 3 being the fastest version, allowing you to go up to 26 mph (as I recall), however there are plenty of electric bicycles that you can buy that will go much faster.
It's 28 mph for Class 3, 20mph for Class 1 & 2, with differences in HOW the power is made available.
The US federal Consumer products definition that was set up over 20 years ago has done a lot towards standardizing requirements nationally.
https://raevbikes.com/pages/e-bike-laws#:~:text=Under%20the%20US%20Consumer%20Product,only%20by%20the%20electric%20motor.
https://www.federalregister.gov/documents/2003/02/12/03-3423/requirements-for-low-speed-electric-bicyclesI think this was a huge factor in helping the industry move forward, since they could standardize on components that could be sold in multiple markets.
One thing that I personally find interesting, is that, there is currently a bit of what I'd consider a loophole, in that manufacturers can use the CONTROLLER to limit power and speed. Many are fitting MUCH more powerful motors than the 750 watt max. that is allowed by the legalese. Like this motorcycle styled bike that has a 2.0kW motor attached:
https://www.coswheelebike.com/products/ct20s-ebikeI've read several accounts and seen videos wherein the factory programmed limits can be removed by finding a firmware hack and loading this into the controller. Presto!, and the bike is now capable of 40+ mph. Anticipating the eventual closure of this "loophole" after somebody's kid does an unsuccessful Evel Knievel into cross traffic, has me thinking I should buy a machine NOW. But the performance / price ratio keeps getting better, every time I look, so I continue to hold off.
I get the impression that our Euro brothers aren't getting access to anything like the same experience. Their market seems to be filled with much lighter machines with much more modestly sized motors, designed for street commuting, not off-road hooliganism, and built to meet their 25 kph limit.
If you want to go faster, grab a license plate and hop on your new "Speed Bike"!
https://www.autoevolution.com/news/friday-27-is-the-fastest-legal-e-bike-in-europe-you-need-a-license-to-ride-one-218100.html#:~:text=Or%20you%20can%20make%20the,25%20kph%20or%2015.5%20mph.