Free Days before Bernese Oberland hike - Anncey or CH?

Not sure about the destination question, but the week long hike is an athlete endeavor. As such I'd pick a place good for warming up and resting up, not going hard and showing up for the main event with a little hammy pull and a blister.

I wouldn't worry much about acclimating to elevation unless you are mountaineering. Elevations are pretty low in the BO for regular mountain travel.

If you want different than mountains and lakes you could easily do Lyon. Or Colmar. There are lovely long walks through the vineyards and interesting mellow hikes in the low mountains of Alsace, and transiting to CH by train is simple and quick

If you are doing the Alpine Pass Route (Via Alpina) from Meiringen to Kandersteg, you will have significant altitude challenges, contrary to the above post. Between Mürren and the Griesalp you will cross the Sefeinenfurka (pass);at 8570 feet. Then from Griesalp to Oeschinensee you will hike over Höhtürli at 9114 feet.

If you live at or near sea level as your profile suggests (nyc), you will want to get started on acclimation to the altitude. At least I would.

I would suggest our own favorite place in Switzerland for this. The village of Bettmeralp is practically right on your way between Geneva and the Berner Oberland. Take. Direct train from Geneva tomBrig and change there for the 15-minute ride to Betten, at the base of the cablecar up to Bettmeralp. Hop on the cablecar and ride up several thousand feet to the village. You will be sleeping at an elevation of 6400:feet and have access by lift or hiking trail to views over the spectacular Aletschgletscher, the larges glacier in Europe. I know of nothing else like this, so it will not “duplicate” the scenery you will enjoy on your hike.

https://www.aletscharena.ch/en/world-natural-heritage-site/great-aletsch-glacier

https://www.aletscharena.ch/en/aletsch-arena/places/bettmeralp

Our favorite hike there goes up the ridge behind the village, then traverses along that ridge above the glacier, to the hut at Marjelensee. You have the glacier below you the whole way (although it is shrunken from what it was when we first saw it 25 years ago.). Or you can ride the lift to the top of the Bettmerhorn for views without hiking. Or take the ridge top trail from Bettmerhorn to the next peak, Eggishorn, which has great views north up the glacier to Konkordiaplatz at the foot of the Jungfrau.

Then descend and take a swim in the Bettmersee to cool off.

From Bettmeralp to Meiringen, you return to Brig by cablecar and short train ride, change to a train to Spiez and on to your starting point from there.

For backpacking I don't worry about acclimating unless sustained time over 9 or 10k. Crossing a couple of 8/9k passes and back down wouldn't trip the sleep high threshold for me, just regular backpacking, particularly without a heavy pack.

I'm not good with elevation either. Mid 50's and fit though - senior and/or inefficient body and/or health issue then definitely acclimate, or if greatest comfort is a priority.

Thanks Lola! Thanks Hank!

Great info.
To clarify one thing. Going to Anncey was just about chilling out and eating. So, we would probably not be doing any sort of strenuous hiking/walking.

That said. It’s probably not a bad idea to go up in altitude to just get used to it. We are healthy 50-ish but I’ve also struggled with those first days at high altitude in the Rockies.
Will investigate your suggestions!!

Well Hank that is great that you can go from Seattle at sea level up and over a 9000 foot pass while carrying an overnight backpack, without huffing and puffing your way uphill. But most people, not just seniors or the unfit, start getting out of breath with exertion above 6000 feet or so, unless they take time to acclimate. I know I do, the first couple of days when we go to our lake cabin at 6300 feet. And I am plenty fit.

Our Tahoe cabin is at 6500'. Easy enough to walk with a backpack 1st day and go high the second day. That's how thousands of people backpack Tahoe every year - drive up from the Bay and go backpacking. Nothing exotic nor heroic nor dangerous. It's just walking a bit more out of breath than usual for the first day and a half.

Maybe OP's hiking tour both doesn't spend a first night and immediately grinds straight up to a 9k pass? If so then a night's sleep at elevation seems wise. Otherwise if they want to first experience some other area besides Switzerland on their trip halfway around the world, it will be just fine to do so.

Well unless you are carrying your backpack to the top of Tallac or Pyramid Peak you are not getting to the elevation of that high pass Lola named. Assuming they are doing the through hike she named. But we don’t know.
Anyway this topic is not about what you can do, it is about the OP and how they want to handle their hike.

Sasha the "pass" between Meiringen and Grindelwald is 6000'. I think that's the route? There are vending machines up there, barns where farmers are making cheese. Meiringen's elevation is 2000'. There's no way a walking tour company is going to grind their guests up a 7,000 ft climb on day one. You don't need to pre-sleep in an altitude tent to do a hut to hut walk in the BO. I don't think I'm being reckless or macho, it's just not that big of a deal, totally doable. It's not Nepal.

If you hit some high passes days later, it's not going to matter that you spent two nights at elevation before you started anyway. It's not necessary to preclude a stay at a different destination ahead of time if that's what OP wants.

I think it’s up to them to decide if they want to acclimate, rather than rely on a stranger who says HE doesn’t need to so they don’t either. And I don’t see what going halfway around the world has to do with it. I would say that just makes it all the more important to be properly prepared for the hike.
And maybe Annecy isn’t such a good choice anyway. The town might not recover from the recent tragedy there by August, who knows. Certainly the affected families will not get over the trauma for a long time.

Annecy does not sound like a very convenient choice in your case, due to transportation logistics.
There is plenty of lakeside charm to be had on Lake Geneva: I would head straight for Montreux or thereabouts (Vevey etc.) for those two nights. It really does not look like the rest of the country, and the language is different, so it will not feel repetitive.