V4.21

All versions

AI is now significantly better at putting together trade offers with the player (ones likely to be acceptable to the player).
Asteroid likelihood in a system increased from 20% to 25%
Ion storm spawn likelyhood an a sector increased from 50% to 65%

Retribution

Minimum star distanced reduced from 7 parsecs to 5 parsecs
Approval requirement for content reduced from 45% to 40%
Civilization capital raw resource production increased from +2 to +3
As hardware continues to become more powerful we have bumped up the number of objects a map can spawn:
Small galaxy base object spawn increased from 300 to 400 (this is how many planets, stars, etc. are allowed)
Medium galaxy base object spawn increased from 500 to 700 (this is how many planets, stars, etc. are allowed)
Large galaxy base object spawn increased from 750 to 900 (this is how many planets, stars, etc. are allowed)
Huge galaxy base object spawn increased from 900 to 1000 (this is how many planets, stars, etc. are allowed)
Gigantic galaxy base object spawn increased from 1000 to 1200 (this is how many planets, stars, etc. are allowed)
Excessive galaxy base object spawn increased from 1400 to 1500 (this is how many planets, stars, etc. are allowed)
Insane galaxy base object spawn increased from 1500 to 1600 (this is how many planets, stars, etc. are allowed)
AI weighting of technologies improved to ensure the AI researches the updated tech tree more effectively
Ministry of Alien Affairs now gives a +0.25 diplomacy bonus
Interstellar Tourism prereq changed from requiring Immigration to ministry of alien affairs to make available earlier in the game.
Supply ship manufacturing cost reduced from 200 to 125
Early game music tracks updated