What is the default Realm Stability game rule in CK3?

Default: The default amount of Factions will arise. (patch 1.20.1.2)

Does changing the Realm Stability rule disable achievements?

No: none of its 13 settings carries the flag blocks_achievements in patch 1.20.1.2.

Game rule · Difficulty · Tweaks · AI

Realm Stability

AI Only: Lesser
Lesser
AI Only: Lesser Limited
Lesser Limited
Default
AI Only: Higher
AI Only: Extreme
Higher
Extreme
AI Only: Higher Limited
AI Only: Extreme Limited
Higher Limited
Extreme Limited

Realm Stability is a game rule in Crusader Kings III (Difficulty, Tweaks and AI) with 13 settings: AI Only: Lesser, Lesser, AI Only: Lesser Limited, Lesser Limited, Default (the default), AI Only: Higher, AI Only: Extreme, Higher, Extreme, AI Only: Higher Limited, AI Only: Extreme Limited, Higher Limited and Extreme Limited. 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 Realm Stability game rule in CK3?: Default: The default amount of Factions will arise. (patch 1.20.1.2)
Does changing the Realm Stability rule disable achievements?: No: none of its 13 settings carries the flag blocks_achievements in patch 1.20.1.2.

13 settings

AI Only: Lesser
A higher amount of Factions will arise, but only for AI rulers.
The script checks it 9 times, in 5 places
Factions 4
- Escalated Peasant Faction
- Nomadic Faction
- Peasant Faction
- Populist Faction
Scripted modifiers (AI weights) 1
- common_faction_modifiers
Every has_game_rule = lesser_realm_stability_ai_only in game/common and game/events, by the top-level object it sits in.
lesser_realm_stability_ai_only
Lesser
A higher amount of Factions will arise.
The script checks it 9 times, in 5 places
Factions 4
- Escalated Peasant Faction
- Nomadic Faction
- Peasant Faction
- Populist Faction
Scripted modifiers (AI weights) 1
- common_faction_modifiers
Every has_game_rule = lesser_realm_stability in game/common and game/events, by the top-level object it sits in.
lesser_realm_stability
AI Only: Lesser Limited
A higher amount of Factions will arise, but only for AI rulers. Populist and Peasant Factions are unaffected.
The script checks it once, in 1 place
Scripted modifiers (AI weights) 1
- common_faction_modifiers
Every has_game_rule = lesser_realm_stability_regular_factions_ai_only in game/common and game/events, by the top-level object it sits in.
lesser_realm_stability_regular_factions_ai_only
Lesser Limited
A higher amount of Factions will arise. Populist and Peasant Factions are unaffected.
The script checks it once, in 1 place
Scripted modifiers (AI weights) 1
- common_faction_modifiers
Every has_game_rule = lesser_realm_stability_regular_factions in game/common and game/events, by the top-level object it sits in.
lesser_realm_stability_regular_factions
Default
Default
The default amount of Factions will arise.
default_realm_stability
AI Only: Higher
A lower amount of Factions will arise, but only for AI rulers.
The script checks it 9 times, in 5 places
Factions 4
- Escalated Peasant Faction
- Nomadic Faction
- Peasant Faction
- Populist Faction
Scripted modifiers (AI weights) 1
- common_faction_modifiers
Every has_game_rule = higher_realm_stability_ai_only in game/common and game/events, by the top-level object it sits in.
higher_realm_stability_ai_only
AI Only: Extreme
A extremely low amount of Factions will arise, but only for AI rulers.
The script checks it 9 times, in 5 places
Factions 4
- Escalated Peasant Faction
- Nomadic Faction
- Peasant Faction
- Populist Faction
Scripted modifiers (AI weights) 1
- common_faction_modifiers
Every has_game_rule = extreme_realm_stability_ai_only in game/common and game/events, by the top-level object it sits in.
extreme_realm_stability_ai_only
Higher
A lower amount of Factions will arise.
The script checks it 9 times, in 5 places
Factions 4
- Escalated Peasant Faction
- Nomadic Faction
- Peasant Faction
- Populist Faction
Scripted modifiers (AI weights) 1
- common_faction_modifiers
Every has_game_rule = higher_realm_stability in game/common and game/events, by the top-level object it sits in.
higher_realm_stability
Extreme
A extremely low amount of Factions will arise.
The script checks it 9 times, in 5 places
Factions 4
- Escalated Peasant Faction
- Nomadic Faction
- Peasant Faction
- Populist Faction
Scripted modifiers (AI weights) 1
- common_faction_modifiers
Every has_game_rule = extreme_realm_stability in game/common and game/events, by the top-level object it sits in.
extreme_realm_stability
AI Only: Higher Limited
A lower amount of Factions will arise, but only for AI rulers. Populist and Peasant Factions are unaffected.
The script checks it once, in 1 place
Scripted modifiers (AI weights) 1
- common_faction_modifiers
Every has_game_rule = higher_realm_stability_regular_factions_ai_only in game/common and game/events, by the top-level object it sits in.
higher_realm_stability_regular_factions_ai_only
AI Only: Extreme Limited
A extremely low amount of Factions will arise, but only for AI rulers. Populist and Peasant Factions are unaffected.
The script checks it once, in 1 place
Scripted modifiers (AI weights) 1
- common_faction_modifiers
Every has_game_rule = extreme_realm_stability_regular_factions_ai_only in game/common and game/events, by the top-level object it sits in.
extreme_realm_stability_regular_factions_ai_only
Higher Limited
A lower amount of Factions will arise. Populist and Peasant Factions are unaffected.
The script checks it once, in 1 place
Scripted modifiers (AI weights) 1
- common_faction_modifiers
Every has_game_rule = higher_realm_stability_regular_factions in game/common and game/events, by the top-level object it sits in.
higher_realm_stability_regular_factions
Extreme Limited
A extremely low amount of Factions will arise. Populist and Peasant Factions are unaffected.
The script checks it once, in 1 place
Scripted modifiers (AI weights) 1
- common_faction_modifiers
Every has_game_rule = extreme_realm_stability_regular_factions in game/common and game/events, by the top-level object it sits in.
extreme_realm_stability_regular_factions

Source: game/common/game_rules/00_game_rules.txt line 540 (key realm_stability), modifiers from game/common/modifiers, names from the English localisation; Crusader Kings III 1.20.1.2.