What is the default End Date game rule in CK3?

1453: The game will end in 1453. (patch 1.20.1.2)

Does changing the End Date rule disable achievements?

No: none of its 2 settings carries the flag blocks_achievements in patch 1.20.1.2.

Game rule · Game Modes

End Date

1453 · default
No End Date

End Date is a game rule in Crusader Kings III (Game Modes) with 2 settings: 1453 (the default) and No End Date. None of its settings disables achievements. Patch 1.20.1.2, from game/common/game_rules/00_game_rules.txt.

This section as JSON: /raw/game-rules.json

Quick answers (2)

What is the default End Date game rule in CK3?: 1453: The game will end in 1453. (patch 1.20.1.2)
Does changing the End Date rule disable achievements?: No: none of its 2 settings carries the flag blocks_achievements in patch 1.20.1.2.

2 settings

1453
Default
The game will end in 1453.
1453_end_date
No End Date
Turns off the end date
The game will not end at any specific given date.
no_end_date_end_date

Source: game/common/game_rules/00_game_rules.txt line 57 (key end_date), modifiers from game/common/modifiers, names from the English localisation; Crusader Kings III 1.20.1.2.