I guided for years in the Andes, Alps and Nepal. Most of my clients lived at sea level. Acclimatization is critical, and fitness isn’t a barometer of how it will go. Everyone’s body adapts differently. My first question is how high have you been before and for how long?
Next, and more important. The Do’s and Don’ts. Do keep drinking caffeine if you regularly do, focus on staying well hydrated and fueled, so hard for so many but if you get behind the curve you can’t catch up. Eat and drink even if not hungry or thirsty.
Practice the mountaineers rest step.
Use pressure breathing to blow excess CO2 out of your lungs, on ascent and descent.
It’s also not a bad idea on quick trips to have Diamox prescribed by a physician for back up. Taken prophylacticly it can be a game changer for some, your choice and talk to your physician about that.
Don’t push too hard too soon, or get sucked along at a pace you can’t maintain because others are going fast, don’t beat yourself up, speak up if you feel off at all. A tiny break can give your body the time it needs to adapt. Again the UA motto of slow is fast will pay off.
My old standard was one day of acclimatization for every 1,000 feet above 8,000ft my clients were climbing for each trip. So, if attempting an 18,000ft peak you need 10 days to acclimatize. Climb high, Sleep low. I know you’re being guided so you may not be able to make this happen, so focus on all the above, on self care, don’t rush and be patient. Aside from that you’ll just need to see how it comes together I’m optimistic you’ll do really well!