As many of you pointed out, there have been serious problems with our pet rarity rating system recently. Pretty much all of our pets (66%) ended up being rated as Uncommon, almost none were Common, and we had no Very Common pets at all!
The way that we used to calculate the rarity of a pet is by counting up all the pets that have been adopted and are currently sitting on Chicken Smoothie accounts, and then dividing that by the number of players on the entire website. That works out how many copies of a pet are available for trade for each person, which is supposed to show you how difficult it'll be to trade for that pet.
The problem with that calculation is that there are a lot of pets owned by people who just don't play CS any more, especially our older pets. But our old rarity calculation decided that those were active pets that you could trade for, even though they're basically stuck on those accounts forever. Also, lots of Chicken Smoothie accounts get created which don't actually log in, or only log in once and don't return, so these accounts aren't actually competing to trade for pets.
So, we've created a new system for working out the rarity of pets! Instead of counting up all of the pets that are on accounts, we only count the ones that are owned by people who are still playing CS (so that pets owned by players who quit long ago don't skew the results.) We also only count active players when we decide how many people are trying to trade for the pets. This makes the rarities much more accurate.
Note that the number of each pet on CS itself hasn't changed - so pets will be just as easy/hard to trade for as they were before. It's just that the rarity label we show for the pet should now be much more accurate and a much better guide for how easy it will be to trade for the pet.
Before you feel sad that you "lost" your only "Very Rare" or "Rare", you just need to realize, it was never really that rare! The old labels were not a good estimate of the pet's true rarity or trading value. The new ones are more accurate. Most newly adopted pets really aren't that rare, since there are a lot of people adopting them. In the past, there were fewer members, so not as many of each pet were adopted. That means those pets really are rarer than current pets, because there are less of them to go around!
As part of this update, we've added a new rarity level "OMG so common". And we've added little rarity bars underneath the pets while trading to make it easier to spot which pets are rare and which aren't

.
OMG so common:
Very common:
Common:
Uncommon:
Rare:
Very rare:
OMG so rare:
OMG so common:
Very common:
Common:
Uncommon:
Rare:
Very rare:
OMG so rare:
Before:
0
0
40
1900
600
370
20
0
0
40
1900
600
370
20
After:
45
430
600
1000
600
350
20
45
430
600
1000
600
350
20