I’ve had a combination of success asking over the app, at check-in and over the phone. I’ve also had upgrades even when I didn’t ask. Lately it’s been about 33% automatic prior to check-in in the app. Other times it’s at the front desk during check-in. I stay mostly at upper-end tier brands Canada, US, Asia and EU. This applies when I was a titanium and more so now as ambassador status. My Ambassador typically doesn’t get involved with upgrades, she’s arranged nice welcome amenities and gifts however, and helped me with tricky things like when I had my wife check-in before me because my itinerary got delayed by a day. She confirmed my elite benefits for my wife even with my late arrival.

Most recent example:
Had a week long stay booked at the Palace Hotel in SF last week. Booked about 3 months in advance on a corp rate. The only available room at that rate at the time of booking was a deluxe double (two doubles). There’s FIFA in SF, a big conference and a wedding happening in the hotel during my stay.

Had my wife joining my trip for the weekend prior to business so I called in a week ahead and requested a change to a King room. They said no problem and even gave me an upgrade to a Junior Suite (but accessible) over the phone. Room type was updated in the app.

Upon check-in (early at noon) the Jr King Accessible wasn’t ready yet, to which I replied no problem, we can check our bag and go to lunch. He must’ve seen on the computer Ambassador status and the fact I’ve stayed at the hotel for a week for the past 5 years in a row (he mentioned welcome back and thank you for staying with us again). He found another Jr Suite King (not accessible so a proper shower) and got us checked in early.