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Stellaris
Stellaris
4.3|Feb 27, 2026
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Stellaris 4.3 "Cetus" Open Beta Updated (2026-02-26)

3/5 Moderate

Mutagenic Spas and Biomorphosis receive major balance overhauls alongside significant trade buffs for Starbases and a fix for Planet Automation.

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Key Changes

  • 1Mutagenic Spa overhaul: Amenities increased to 500 and expanded district placement.
  • 2Biomorphosis ascension path reordered with major changes to leader and empire size modifiers.
  • 3Starbase trade buffs: Offworld Trading Company and Hyperlane Registrar trade output significantly increased.
  • 4Planet Automation restored and fixed after being non-functional.
  • 5Social Welfare living standard nerfed, reducing both happiness and unity production.
  • 6Experimental Sentencing rework: Experimentation Chambers now scale with crime and Penal Colonies.
  • 7Synthetic Ascension nerf: Removed the -90% housing bonus for partial virtuality.
  • 8Tradition renames: Mercantile and Unyielding changed to Commerce and Fortification.
  • 9Combat stability fix: Reduced stack usage to prevent crashes in large fleet battles.
  • 10Resource building buffs for Food Processing, Mineral Purification, and Energy Grids.

All Changes

📜Traditions(2)

  • changeMercantile: Renamed Mercantile tradition to Commerce to match standard naming conventions.
  • changeUnyielding: Renamed Unyielding tradition to Fortification to match standard naming conventions.

🏢Buildings & Districts(15)

  • nerfMutagenic Spas: Mutagenic Spas now only grant the Substance Abuser trait to the governor of the planet where they are built.
  • buffSpa Attendants: Spa Attendants for Worker Coops now provide a buff to Union Stewards.
  • buffSpa Attendants: Non-corporate Spa Attendants amenities production increased from 100 to 500.
  • changeSpa Attendants: Corporate Spa Attendants now provide 2 trade value.
  • buffMutagenic Spa Councilors: Mutagenic Spa Councilors now increase the number of spa attendant jobs, with higher effects if they are a substance abuser.
  • buffMutagenic Spas: Mutagenic Spas can now be placed in research or unity district specializations.
  • buffFood Processing: Increased the resource bonuses provided by Food Processing buildings.
  • buffMineral Purification: Increased the resource bonuses provided by Mineral Purification buildings.
  • buffEnergy Grid: Increased the resource bonuses provided by Energy Grid buildings.
  • changeExperimentation Chambers: Experimentation Chambers now provide a static number of experiment engineer jobs and scaling test subject jobs based on building tier.
  • buffExperimentation Chambers: Test subject jobs from Experimentation Chambers are increased by 50% on Penal Colonies.
  • changeExperimentation Chambers: Rebalanced research production for experiment engineers based on planet crime; fixed bug regarding uncapped crime modifiers.
  • nerfExperimentation Chambers: Consumer goods upkeep for experiment engineers now increases with planet crime levels.
  • removeOrderlies: Orderlies no longer reduce housing requirements on the planet.
  • changeOrderlies: Orderlies now increase the job efficiency of experiment engineers and test subjects instead of direct output.

👤Leaders & Traits(2)

  • nerfRuthless Developer: Halved the effects of the Ruthless Developer trait on workers and slaves.
  • nerfUnifier: Unifier trait effects no longer scale with leader level.

⚙️Gameplay Systems(4)

  • nerfSocial Welfare: Reduced happiness bonus provided by the Social Welfare living standard.
  • nerfSocial Welfare: Reduced unity production from civilians under the Social Welfare living standard.
  • changeComputation Core Focus: Computation Core Focus policies now grant +2.5% job efficiency per 100 roboticists/identity designers (was +0.5% per 100 civilians).
  • changePirates: Adjusted scaling of event-spawned pirate fleets to be more reasonable for 4.3 balance.

🧬Ascension & Species(8)

  • changeBiomorphosis: Switched the positions of Optimized Neurology and Heightened Attributes in the Biomorphosis tree.
  • changeBiomorphosis: Switched the positions of Biochemical Composure/Regenerative Cloning and Artificial Population in the Biomorphosis tree.
  • nerfBiomorphosis: Removed Organic Job Efficiency bonuses from Somatic Subversiveness and Artificial Population.
  • changeOptimized Neurology: Optimized Neurology now grants -1 Leader Maximum Negative Traits instead of +1 Effective Leader Level.
  • buffSomatic Subversiveness: Somatic Subversiveness now grants an additional +1 Effective Leader Level.
  • changeArtificial Population: Artificial Population now provides -10% Empire Size from Vat Grown pops.
  • changeImperfection Remediation: Moved the -10% Empire Size from Pops modifier from Heightened Attributes to Imperfection Remediation.
  • nerfSynthetic Ascension: Adopting partial virtuality via Synthetic ascension no longer grants -90% housing for organic, lithoid, or infernal species.

🛰️Starbases(3)

  • buffOffworld Trading Company: Offworld Trading Company now grants +4 trade per Trade Hub module (increased from +2).
  • buffHyperlane Registrar: Hyperlane Registrar now grants +2 Trade per Trade Hub module (was a flat +2) and adds the Subspace Amplifier aura.
  • newHyperlane Registrar: Added Subspace Amplifier aura to Hyperlane Registrar, providing -40% Hyperlane and Jump Drive cooldown/charge time.

🐛Bug Fixes(21)

  • fixPlanet Automation: Fixed Planet Automation scripts to ensure they work correctly again.
  • fixPlanetary Populations: Fixed reversed happiness check for founder species that applied incorrect amenities buffs.
  • fixCouncil: Fixed council position flavor text to correctly display renamed titles.
  • fixSubterranean: Fixed Subterranean origin not providing extra housing on mining districts.
  • fixCyber Imperials: Fixed stability bonus missing from Cyber Imperial nobles.
  • fixWenkwort: Wenkwort planet modifiers are now correctly removed if the planet is no longer a Gaia world.
  • fixTechnologies: Fixed incorrect housing modifier values on several technologies.
  • changeChosen of the Eater: Updated Gestalt version of Chosen of the Eater to match non-gestalt changes.
  • fixBiomorphosis: Fixed Mutation and Cloning ascension paths being unable to remove advanced traits.
  • fixProspectorium Optimizer: Fixed modifiers for the Prospectorium Optimizer trait.
  • fixUI: Fixed an issue with ship size map icons.
  • fixDomination: Corrected erroneous tooltip for the Domination tradition finisher.
  • fixCivics: Corporate Vampires and Entropy Drinkers can now be swapped seamlessly during government transitions.
  • fixDistricts: Fixed secondary district names for Spiritualist empires and Ring Worlds.
  • fixCrisis: Added abort triggers for Prethoryn, Unbidden, and Contingency event chains for proper cleanup after defeat.
  • fixEndbringers: Endbringers can no longer be declared a crisis if they are already the active crisis.
  • fixHive Minds: Fixed inverted happiness calculation that caused Hive Minds to receive unintended bonuses.
  • fixSector Governor: Fixed sector governors failing to propagate non-triggered trait modifiers to all planets in a sector.
  • fixUI: Cleaned up modifier tooltips to remove unintentional data like 'planet:'.
  • fixFleet Modifiers: Fixed ship/fleet special modifiers (like docked upkeep reduction) not applying to the simulation.
  • fixCombat: Reduced stack usage in combat targeting to prevent crashes (CTD) in large-scale battles.

⚡Performance(5)

  • changeEngine: Reduced the total number of memory allocations.
  • changeEngine: Optimized string allocations and localization lookups.
  • changeEngine: Reduced repeated localization lookups when calculating planetary modifiers.
  • changeEngine: Moved modifier name calculations to tooltip generation to reduce simulation load.
  • changeEngine: Micro-optimized the localization system to reduce recursion and length calculations.

Summary

Balance & Reworks

This update focuses heavily on refining the 'Cetus' Open Beta, specifically targeting the Mutagenic Spas and Biomorphosis ascension paths. Mutagenic Spas now offer significantly more amenities (up to 500) and have expanded placement options, while Biomorphosis has seen a complete reordering of its progression tree and stat adjustments. Experimental Sentencing has also been reworked to scale with crime and penal colonies.

Economy & Starbases

Starbase trade modules received a notable buff, with the Offworld Trading Company doubling its trade output per module and the Hyperlane Registrar now scaling with Trade Hubs while providing a new subspace aura. Conversely, Social Welfare and certain leader traits like Ruthless Developer and Unifier have been nerfed to balance early-game scaling.

Technical Improvements

Planet Automation has been restored after being broken in previous builds. The update also includes critical performance optimizations regarding memory and string allocations, alongside a fix for a combat-related crash (CTD) involving large ship counts.

← OlderStellaris Dev Diary #411 - Our Next 4.3 ExperimentFeb 26, 2026Newer →Stellaris 4.3 "Cetus" Open Beta Updated (2026-03-04)Mar 4, 2026

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