I was sad when I bought a new 10th or 11th gen X1 carbon to replace my 4th gen. I configured them essentially the same, second-to-fastest processor, FHD display, no touch screen.
The 4th gen almost never kicked its fans on, especially in Linux. The new one gets far hotter, even at idle. Lenovo removed the traditional sleep mode in favor of modern sleep, which causes it to die with the lid closed in a couple days compared to over a week with the 4th gen.
I can't keep the gens straight because I bought a late-model right after a new gen was released. It's definitely not the 9th because lenovo basically said "don't buy this", and it's the model before they added the awful external camera bump for a webcam I'd use 2x a year.
Ironically, battery life while actively using it is decent, not as good as the 4th gen, but I could squeeze 8 hours out of it. I use whatever cpu throttling utility that lives under the default KDE power controls. I trust it works because compilation times are quartered when you go from power saving to high performance.
Most of my complaints revolve around the fact I can't enable legacy sleep modes that actually save power. I blame microsoft for pushing their new sleep modes that mostly benefits windows.
The 4th gen almost never kicked its fans on, especially in Linux. The new one gets far hotter, even at idle. Lenovo removed the traditional sleep mode in favor of modern sleep, which causes it to die with the lid closed in a couple days compared to over a week with the 4th gen.