Mixing RAM speeds works, but not how you'd expect.

Yes, but you’re stuck at the slower speed. The system will downclock the faster stick to match the slower one, so that DDR4-3200 will run at 2666 MT/s if paired with a DDR4-2666 module.

The bigger issue with soldered RAM is that you can’t swap it. The socketed stick is the only one you have control over. So if the soldered RAM is slow, your upgrade is capped. And if the timings or voltages don’t line up well, you might get instability—crashes, blue screens, random restarts.

It usually works, especially with same-generation DDR4 from reputable brands. But don’t expect the faster stick to do any heavy lifting. You’re paying for speed you won’t use.

Future You might wish you’d just bought a laptop with replaceable RAM.