Stellaris 4.3 "Cetus" Open Beta Updated (2026-02-26)

Hello Stellaris Community!

We're back updating the "Cetus" Open Beta again, with more balance changes based on your feedback as well as more bug fixes and performance improvements.

Please note: Next week's Open Beta update will contain a save breaking change to pop groups. There will be a rollback branch available for those who want to continue your saves from this version.

4.3 ‘Cetus’ Open Beta Patch Notes 2026-02-26​

Improvement​

• Renamed Mercantile and Unyielding traditions to Commerce and Fortification to match the naming structure of all other traditions.

Balance​

• More Mutagenic Spa balance:

  • Mutagenic Spas now only grant Substance Abuser to the governor of a planet with the baths on.

  • Spa Attendants for Worker Coop buff the Union Stewards.

  • Non-corporate Spa Attendants now produce 500 Amenities (was 100). Corporate Spa Attendants now provide 2 trade.

  • Mutagenic Spa Councilors now increase the number of spa attendant jobs, this effect is amplified if they are a substance abuser.

  • Mutagenic Spas can now be placed in research or unity district specializations

  • Increased the bonuses from Food Processing, Mineral Purification, and Energy Grid buildings.

• Experimental Sentencing changes:

  • Experimentation Chambers now provide a static number of experiment engineer jobs, and a scaling number of test subject jobs (depending on building tier). The number of test subject jobs is increased by 50% on Penal Colonies.

  • Rebalanced the amount of research experiment engineers produce per crime on the planet. The bug in which the modifiers considered the uncapped crime on the colony has also been fixed.

  • Consumer goods upkeep of experiment engineers now also increases with crime.

  • Orderlies no longer reduce housing requirements on the planet.

  • Orderlies now increase the job efficiency of experiment engineers and test subjects not their output.

• Halved the effects on workers and slaves of the Ruthless Developer trait.

• Unifier trait effects no longer scale with leader level.

• Reduced happiness from Social Welfare.

• Reduced unity from civilians under Social Welfare.

• Biomorphosis changes:

  • Switched Optimized Neurology (Purity flex 1) and Heightened Attributes (Purity flex 2).

  • Switched Biochemical Composure/Regenerative Cloning (Cloning flex 2) and Artifical Population (Cloning flex 3).

  • Removed Organic Job Efficiency bonuses from Somatic Subversiveness (Mutation flex 2) and Artificial Population.

  • Optimized Neurology now gives -1 Leader Maximum Negative Traits instead of +1 Effective Leader Level

  • Somatic Subversiveness now grants an additional +1 Effective Leader Level.

  • Artificial Population now provides -10% Empire Size from Vat Grown pops

  • -10% Empire Size from Pops from Heightened Attributes moved to Imperfection Remediation.

• Starbase building Offworld Trading Company now grants +4 trade per Trade Hub module (was +2 Trade).

• Starbase building Hyperlane Registrar now grants +2 Trade per Trade Hub module (was a non-scaling +2 Trade) and adds the Subspace Amplifier aura to the Starbase (-40% Hyperlane and Jump Drive cooldown/change time).

• Adopting partial virtuality by undergoing Synthetic ascension as an organic, lithoid or infernal species no longer grants -90% housing.

• The Computation Core Focus policies now grant +2.5% job efficiency per 100 roboticists or identity designers instead of +0.5% per 100 civilians.

• Adjusted scaling of event spawned pirate fleets to be more reasonable for 4.3 numbers.

Bugfix​

• Planet Automation should work again. A design pass is in progress to improve the scripts.

• Fixed founder species has happiness check being reversed applying wrong amenities buffs on planetary populations

• Fixed the flavor text of a number of council position displaying the default name instead of the renamed title if the player had renamed them.

• Fixed Subterranean origin not giving extra housing on mining districts.

• Fixed nobles from cyber imperials not giving stability.

• Wenkwort planet modifiers are now correctly removed if the planet stops being a gaia world.

• Fixed a number of technologies having incorrect amounts for the housing modifiers they provide.

• Updated the Gestalt version of Chosen of the Eater to match the changes made to the non-gestalt version.

• Fixed mutation and cloning ascension not being able to remove advanced traits.

• Fixed modifiers from the Prospectorium Optimizer trait.

• Fixes an issue with ship size map icons.

• Corrected erroneous tooltip for the Domination tradition finisher.

• Corporate Vampires and Entropy Drinkers can now be swapped seamlessly when transitioning between corporate and oligarchic .governments

• Fixed several issues with secondary district names for Spiritualist empires and Ring World districts.

• Added abort triggers for the Prethoryn, Unbidden and Contingency event chain so they get properly cleaned up after their related crisis is defeated.

• Endbringers can no longer be declared a crisis if they are already the current crisis, which was restarting their war.

• Fixed incorrect founder species have happiness calculation resulting in inverted behavior that caused for example hive minds getting happiness bonuses.

• Fixed sector governor missing propagation of non triggered trait modifiers to all planets in the sector and not only the capital.

• Adjusted various conditions in modifier tooltip generation to not show unintentional data, ex “planet:”

• Fixed ship/fleet special modifiers being applied properly to the simulation and not only show up in tooltip ex docked ship upkeep reduction.

• Reduced stack usage in combat targeting code that could cause a CTD/undefined behaviour when larger numbers of ships are involved in combat.

Performance​

• Reduced number of memory allocations

• Optimized string allocations

• More string optimizations

• Reduced repeated localization lookups when calculating planet modifiers

• Moved modifier name calculations to tooltip generation where this was done in the game simulation.

• Micro optimized localization system even more, reducing amount of allocations, recursions and length calculations.

For the entire set of 4.3 Open Beta patch notes, please visit the paradox forums**.**

You can leave your feedback on the latest version of the open beta here: https://pdxint.at/4rN5fU1 and if you experience a bug or other issue, please make a bug report!

Thank you all for your interest in the 4.3 "Cetus" Open Beta, and thank you for playing Stellaris!