Hi there-
I have a layover in Frankfurt airport on my Lufthansa flight from Johannesburg to Houston. I was just wondering if I only have a few hours layover and am not going out of the airport, do I still end up having to get my passport stamped? I am a US citizen. My luggage is checked through to my final destination so I don't have to go out and re-check it.
Thanks.

With those flights, you won't go through passport control or get your passport stamped at FRA.

"do I still end up having to get my passport stamped?"

Not if you don't want to.

By default, air passengers making same-booking international transfers remain airside, and usually escape passport inspection.

That's not the case for most transfers in the US, but is the case in virtually all other developed democracies. But if you want a German stamp, and have nothing else to do, you can queue up, go through Schengen immigration, then queue up again to go through security and outbound passport control.

Compared with many other options at many international airports, that might be exciting. It also allows you to go to the sex cinema in the airport basement.