The problems with CF bikes aren't usually to do with the carbon bit at all, but the resin. There will be different qualities of this from different manufacturers. The carbon fibres prob do have an infinite fatigue lifespan. Steel is pretty high. Al is low.
If you have a crash and crush some of the resin, it is permanently damaged. Very thin tubes of CF+resin might flex without damage to the resin.
I used to race kayaks. One boat I had was built by a small kayak manufacturer, for the manufacturer's son. No expense spared on the materials; so they used the highest grade epoxy available. Most kayaks were built with polyester back then. (this was a flat water kayak, 17'6" long, weighing less than 20lb)
I hit a rock . The only damage was a minute chip.
My other boat, weighing twice as much, would have holed in the same situation.
I'm betting it's the same with CF. Very high-end bikes will last longer.