Faster Internet bandwidth between common ISPs?

Let's say I have an office in Dallas, and an office in Los Angeles. Both of these offices have AT&T dedicated fiber. Would I be guaranteed higher bandwidth between these two locations than say, using Spectrum for one office instead?

I'm imagining that I'd be able to take advantage of some kind of AT&T backhaul between the two, but I don't know that for a fact. Is it all just the general internet once you leave a local ISP? I've tried looking for documentation on this kind of thing, but I feel I'm a bit out of my element.