Population required for every additional specialty district is reduced by 1. So a city can build another district at pop 3, 5, 7, 9 and so on. (was every 3 pop in base game).
With 2.8, eras are longer than in the base game and getting stuck for a long time in a dark age can really suck, therefore:
Citizen pressure (loyalty) for golden and heroic ages reduced to 1.25 (was 1.5)
Pressure from dark age increased to 0.75 (was 0.5).
Increased resource cost for units in the Medieval and later eras slightly.
Barracks and Stables now get +2 production to encourage AI to build them (was +1).
Gold cost of upgrading units increased to 150% of production cost, so highly promoted will be a bit more expensive to upgrade (was 100%).
Crossbowman now upgrades to Ranger (was Field Cannon).
Removed adjacency bonus for Commerical Hubs and Harbors of Gold from every 2 adjacent districts.
Harbors get +1 gold for every adjacent Camp.
Commercial Hubs now get +1 Gold for every adjacent Neighborhood.
Kurgan improvements now start with 2 Gold (was 1).
Kurgans provide +1 loyalty to city.
God of the Sun provides 2 Faith (was 1).
Goddess of the Hunt providdes 2 Faith (was 1).
Metal Casting is slightly more expensive. Costs the same as Mass production.
Brazil's trait has been reworked again.
Now Campus, Commerical Hub and Theater Square receive +1 adjacency bonus for every 2 adjacent Rainforests. Holy sites are unchanged.
Updated texts in the Civilopedia to reflect some changes by the mod.
Updated texts for district projects to add more specific info about rewards.
Agricultural Revolution Expanded (AREX) 2.8.6
Tech tree changes, naval movement increased, aiming for historical "accuracy"