As I understand it, the Irvine Company had offered to provide affordable units in most of it's apartment complexes in Irvine many years ago. If you look around, you'll see that most IAC (irvine aparment commun) communities do have a set aside of affordable units. I believe this is a documented agreement between the Irvine Co and the City of Irvine, you can probably find it on the city records website, i'm too lazy though. But, i guess my point is, the IAC implemented this program as a gesture of good faith to the city the were essentially building.
There are three affordable rent rate tiers ,moderate, low and very low and are calculated by the state or maybe city or maybe county (all this affordable stuff is very ambiguous). Moderate rent rate is roughly equal to 1/3 of 120% of the area median income, in Irvine i believe it's city median income, in LA it's County median income. These will be leased as moderate; low and very low income units are significantly cheaper and attract...errr....undesirables. (I used to live a few blocks down from some in Irvine, near the culver 99 ranch mkt, and i would actually see drug deals in the culdesac).
Very doubtful they will receive affordable housing tax credits, as a developer must apply to the state for these and it's a competitive, brain damaging process and I believe most credits are awarded to communities that provide 100% affordable housing. However, per SB 1818, a developer is entitled to certain incentives if they provide 25% moderate income housing in their development which could mean density bonus, height increase, fee reduction, etc. Not sure if IAC can take advantage of that due to the building code or due to the City having no idea how to implement this 3 two year old state law, at least they didn't when i was working on projects there.
IR, I really wish that were true, but this here Great Park (ya know the overside ballon ride) is going downhill fast due to some pretty terrible local government officials and it's affecting the Irvine Co as well.