How far in advance you usually look for these? Any pattern?

I'm not really seeing any pattern, just randomly looking through availability in Dec., Jan., and Feb.

The easiest way that I have found to look for F availability on CX regional flights is on Google Flights. Select Class = First, then enter HKG as point of origin, then "MNL,BKK,TPE,SIN" as destination (can have up to 5 points of origin and 5 destinations separated by a comma and a space). Select Stops = Non-stop, and Airline = Cathay. Then click on the little 31 symbol to the left of the departure date and scroll through the months. Doing this is, it is clear there is no F on CX flights to any of the 4 destinations mentioned after March 24th.

It looks like from April onwards only HND will have CX regional flights with F.

How far in advance have you booked it? Flight report is very welcomed btw, if you will have time to.

I suspect the aircraft with F used for regional Asia will be used for the new destinations of Brussels, Dublin and Copenhagen this year.

Really? I thought all three, or at least two of the three, would be served by 35G/35Ks without F?

Yes, they'll all be operated by the 35G, so that's probably not the reason the 77Hs are being taken off regional flights. But I suspect they'll still feature intermittently on TPE/BKK/SIN closer to date.

I booked CX 701 on 3/11 in F. Now it's been downgauged to a regional 773. Is there a chance they'll upgauge it? And if so, I imagine I wouldn't automatically be switched back to F, which was the original booking class.

It could change multiple times before departure, and then again on the day of departure.

So here's where things get interesting. On the same flight for my friend, I made an Avios booking for PEY. They've now been upgraded to U class in J. If the aircraft is changed again, would he automatically be downgraded back to PEY?

The down gauge happened to my 3/14 CX751 flight too. Interesting to see (through Google flights) that beyond March 24, BKK no longer sees any F option on CX.

My advice is ignore Google flights. Good for many things, but definitely not for figuring our CX's plane rostering. We get folks frequently inferring this and that about CX's schedule due to Google Flights, and usually it ends up wrong.

My bet is CX will continue to do to BKK with F as it has for years on end: schedule F intermittently, and then swap it away when it suits them, including at the last minute.

Odd comment, in that Google flights reflects exactly what is on CX's website and serves immediate changes.

Haha mate, I'm just here to provide useful information to posters based on what I'm quite familiar with. I have no doubt you're correctly repeating what's on Google Flights or the CX website.

However, despite what you see (I haven't checked, but I presume you're right), that still doesn't mean anything if you're unfamiliar with how CX operates F to BKK, TPE, and to a lesser extent SGN and MNL. I'm just speaking from a decade of 60-80 a year purchased segments on CX/KA, mostly in J and F. I feel pretty confident F is not permanently disappearing from BKK simply because you can't find it in the schedule past March. It happened like that last year too, and lo and behold it reappeared a month later. Similar situation happened with TPE a month ago.

I also think its likely F will continue to be a merry round of equipment and disappoint folks who buy it or redeem it in F when it does reappear.