• Eliminating all the other Empires
• Vassalizing all the surviving Empires
• Rending the world unfit for human life

• Completing the Technology tree (every endgame tech)
  • This currently feels like a dynamic turn limit as it scales to the performance of cultures in game and could be thought of as world ending (if you assume this results in researching tech that ultimately ends the planet or time itself)
• Sending a Mission to Mars
  • The classic civilization style, I leave it on primarily for the civ memories. Its also a way you could control ending the game if you are winning, others you only have indirect control. 

• Reaching the last turn (300 turns on Normal Game Speed)
  • The turn limit feels like it should be on, but as most games seem to end by this currently been experimenting with this off. This should be a last resort for games going on way too long. Or I and partner still playing badly which is why we keep hitting the turn limit.
• Earning every Contemporary  Era Star (a total of 21 stars)
  • This one I'm not sure about. I haven't had a game end because of it yet but something about ending the game because someone gets all fame stars just feels odd, still currently enabled though.

When i play on blitz, I usually opt for only having the space race, pollution, and empire elimination end game conditions. I usually end up building the mars rocket when I feel like it’s time to end the game, so usually around turn 110-120 on blitz.