Population

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This article is for the PC version of Stellaris only.

Population, also known as pops, is the center of productivity and political action within an empire. They provide resources by working in jobs created by districts and buildings, and also produce unity if they are part of a specific faction.

Demographics[]

Each planet has three variables that determine its demographic dynamics. At any time a planet can have only one growing pop, one declining pop and one assembling pop, and their speeds determine the demographics.

Pop growth[]

Update 3 growth surface plot — Growth as a function of planet capacity and population

Pop growth represents the increase in population from natural reproduction and immigration. Its unit of measurement is pop per month. Growth points accumulate every month by adding the month's pop growth, and after reaching a growth progress goal a new pop appears. The growth progress goal is dynamic and depends on the total empire population: growth progress goal = 100 + growth required scaling × total empire population

The growth required scaling value is a game setting. The more pops a empire has the more growth points are needed to be accumulated for the next pop.

Monthly pop growth is a function of

the base pop growth: a sum 3.0 pop/month and pop growth from pops
percent bonuses for pop growth
migration per month
percent bonuses for pop migration:

$\text{pop growth} = (3.0 + \text{pop growth from pops}) \cdot ( \sum \text{percent bonuses for pop growth}) + \text{migration} \cdot ( \sum \text{percent bonuses for migration})$

The base pop growth is depends on the number of pops on the planet and a logistic curve-like dictated by the planet capacity value. Then pop growth modifiers are applied. And lastly pop growth from immigration/emigration is added/subtracted with its modifiers.

Base population growth formula:
Condition	Formula
$\frac{{\text{planet capacity}}}{2} > {\text{planet population}}$	$\text{total base growth} = 3 \cdot \max (0.125 \cdot (\text{population} - \frac{\text{population}^2}{\text{planet capacity}} - 1) , 1)$
$\frac{{\text{planet capacity}}}{2} \le {\text{planet population}}$	$\text{total base growth} = 3 \cdot 0.125 \cdot (\text{population} - \frac{\text{population}^2}{\text{planet capacity}} - 1)$

Graph Pop vs Planet Cap vs Growth — Amount of pops on the planet (X axis). Planet capacity (Y axis). Color and value - pop growth. Marked regions: Light Orange - zero growth, Cyan - minimal growth (0.3 per months), Pink - overcrowding, Light Green and Green - standard growth (3.0) and better, Gold - growth cap (4.5). Values on the border of the Gold zone are the corresponding values for population amount for that cell - to make lookup convenient

On the left is a plot of base population growth as a function of the planet's population from 1 to 99 (X axis) and the planet's capacity from 15 to 104 (Y axis). For reference a number of planet capacity values for zero development cases are given in the table:

value	planet type	value	planet type
15	small Habitat	63	Ring World Sector
21	medium Habitat	83	Planet size 20
29	big Habitat	103	Planet size 25
62	Planet size 12

Base pop growth values spawn between minimum of 0.3 per month (Cyan color) and the maximum value of $(\text{logistic growth ceiling} \cdot 3)$ growth per month (Gold color on the graph). The logistic growth ceiling game setting determines the maximum base growth. By default: $\text{logistic growth ceiling} = 1.5$ ; $\text{Max Base pop growth} = 4.5$ .

The plot of the base pop growth has the following features:

feature	Value	Color	Growth	Condition
plateau	0	Light Orange	no growth	extreme overpopulation
slope	0 - 3.0	Pink	bellow average	growth but with overcrowding
plateau	3.0	Light Green	standard 3.0 and no pop growth from pops	seen for planets of all sizes in the case of a small population
slope	3.0 - 4.5	Green	good growth	not yet optimal condition
plateau	4.5	Gold	maximum pop growth	Optimal condition for pop growth

Species can be chosen manually for growth if the Population Controls policy is set to Allowed. Otherwise it is done automatically following in game logic: any species existing on the planet or which has immigration access to the planet may be selected to grow there. When choosing a species to grow, planets will generally prioritize species that are under-represented on the planet and have citizenship equal to that of the already existing species. If immigration access is lost to all planets containing the currently selected species, a new species will be selected and all existing growth progress will be erased.

Pop growth stops when a planet is 15% overcrowded and has 5 pops without housing. Pops start to decline when a planet is 25% overcrowded. Planet capacity is capped at 500, regardless of free housing or unblocked districts. Pops can go over 500 and will not stop growing (or decline) until the required housing exceeds available housing by 15% (or 25%).

Habitability is an important pop growth modifier. Pops on low habitability planets will reproduce slower and migrate. Every 1% reduction of habitability below 100% reduces species growth by −0.5%. At 0% Habitability pops have −50% growth speed.

Migration[]

Migration is calculated by subtracting emigration push from immigration pull, both of which are determined by factors such as housing, stability and unemployment. A planet with more emigration than immigration will have its growth speed lowered and the amount lowered will be added to potential immigration targets. Planets with higher immigration pull will receive a greater share of this migration, which is converted directly into pop growth. Signing a migration treaty will allow migration to and from another empire's planets. A newly colonized planet gains +100 immigration pull and divides a total of +50 emigration push between all developed planets, until 15 years have passed or the colony has 10 pops.

40% habitability is the minimum that will be considered for automatic migration.

Growth weight[]

The exact mechanics by which a new pop is selected for growing/assembly is not fully known. However a bunch of values can be extracted from the Stellaris/common/defines/00_defines.txt file.

Name	Value	Description
New_Pop_Species_Randomness	0.5	The higher this is, the more random species selection of new pops will be
New_Pop_Same_Species_Weight	1.0	The higher this is, the more new pops will be weighted by number of same or subspecies pops
New_Pop_Exact_Species_Weight	0.5	The higher this is, the more new pops will be weighted by number of exact same species pops
New_Pop_Slavery_Weight	0.25	The higher this is, the more new pops will tend to be balanced between enslaved and non-enslaved species
New_Pop_Species_Div	0.05	The higher this is, the more planets will tend to grow species that are underrepresented on the planet
New_Pop_Habitability_Threshold	0.75	If habitability is under this, apply exponentially increasing penalties to new pop weight
New_Pop_Homeworld_Mult	2	Pops have increased weight for growing on their homeworld
New_Pop_Growth_Mod_Mult	0.33	How much does species growth mod trait matter for new pop weight
NEW_POP_Immigration_Mod_Mult	1	How much does species immigration growth mod trait matter for new pop weight (when there is immigration)
Pop_Decline_Threshold	3.0	A species will decline when there is another species with a growth priority this many times higher

Pop assembly[]

Pop assembly represents a planet's capacity for constructing Mechanical, Machine, or biological pops. Pop assembly can be either robotic or biological at a given time; both cannot be produced simultaneously. Once $100 + (\text{growth required scaling} \cdot {\text{total empire population}})$ assembly points are reached, a new pop is created on the planet. Non-sapient robotic pops do not migrate but can create overcrowding and unemployment. The constructed template is the one with the highest number of used trait points, but can always be changed manually; unlike choosing a species to grow, this does not cause a penalty to assembly speed.

Robotic pop assembly is affected by traits and other modifiers.

Organic pop assembly is not affected by any traits or modifiers except for the following:

+5% per Medical Worker Job
−25% from Lithoid
−75% from Necrophage

Assembly type		Source	Other requirements
Robotic pop assembly	+2	Roboticist jobs	Robotic Workers technology
Robotic pop assembly	+1	Replicator jobs	Machine Intelligence authority
Organic pop assembly	+2	Spawning Drone jobs	Hive Mind authority
	+2	Reassigner jobs	Permanent Employment civic
	+3 or +4.5	Clone Vats buildings	Engineered Evolution ascension perk, extra with Stem Cell Stimulation
	+2 to +15	Ancient Clone Vat buildings	Clone Army origin
	+0.02	Each pop with the Budding trait
	+0.05	Each pop with the Polymelic trait	Genetic tradition complete Leviathan Transgenesis technology defeat Tiyanki Matriarch

Pop decline[]

Pop decline represents the decrease of certain species on the planet due to purging or severe overcrowding. A pop will disappear after 100 decline points have been accumulated. By default, decline rate is −5 decline points per month. Overcrowded planets that have over-represented species will have those species begin to decline in numbers and be replaced by newly growing, under-represented species that have equal citizenship. Purging a particular species will cause that species to decline more rapidly depending on the purge type; the decline factor from purging overrides natural decline factors.

Resettlement[]

Resettlement is the process of pops moving from one planet to another, more desirable one.

Automatic resettlement[]

Sapient, unemployed, free pops have a chance each month to automatically resettle to another planet with available jobs and housing and suitable habitability. If a Slave Processing Facility is active on the planet, enslaved pops and robots in servitude are also eligible. Pops cannot automatically resettle from planets that have been colonized for less than 61 months.

Migration controls will prevent this (except for sapient robots). Empires that outlaw slavery (and hence the slave processing facility) cannot enable automatic resettlement for robots in servitude.

A Transit Hub starbase building will increase the monthly chance of a pop automatically resettling.

Forced resettlement[]

If the empire's Resettlement policy allows it, forced resettlement will instantly move a pop from one planet to another. This costs a base amount of energy and unity determined by the pop's stratum, which may be reduced by additional modifiers.

Pop Stratum	Allowed?	Base cost
Pop Stratum	Allowed?
Ruler	Policy	500	50
Specialist	Policy	250	25
Worker	Policy	100	10
Complex Drone Menial Drone	Always	100	10
Slave	Policy	50	0
Bio-Trophy	Always	100	25
Purging Assimilation	Always	100	0
Robotic servitude	Always	100	0
Subversive	Never	n/a

Modifier source	Cost
Modifier source
Evacuation Protocols edict	−50%
Appropriation tradition	−33%
Operational Proxies tradition	−33%
Corvee System civic	+0%	No cost
Subsumed Will civic	+0%	No cost
OTA Updates civic	+0%	No cost
Starborn trait	−25%
Nomadic trait	−25%
Sedentary trait	+25%

Happiness[]

Each pop in an empire has a happiness rating. It ranges from 0% to 100% and has a base level of 50%. Happiness determines approval rating when combined with stratum political power, as well as the following effects:

Each point of happiness above 50 adds +1% governing ethics attraction to free pops and +2% Authoritarian ethics attraction to slaves.
Each point of happiness below 50 adds −1% governing ethics attraction to free pops and +10% Egalitarian ethics attraction to slaves.
Each point of happiness above 50 gives each pop −0.02 crime, up to 0 per pop at 100% happiness.
Each point of Happiness below 50 gives each pop +0.02 crime, up to +2 per pop at 0% happiness.

Fortunately, there are many ways to improve happiness in an empire. Planetary edicts, civics, living standards, permanent modifiers, planet modifiers, and ruler traits can positively affect happiness.

Faction approval also plays a major role in pop happiness and Events may have an impact on planetary or empire happiness for a limited time as well.

Approval rating[]

Pop approval rating is a measure of the population's support towards the empire. It is determined by the average happiness of each stratum, weighted by political power. Pops without happiness are treated as having 50% happiness (for example: pops with Nerve Stapled trait, pops with Machine trait). The displayed approval rating is rounded down, as is the displayed stability bonus.

$\text{Approval Rating} = \frac{ \sum_{}^\text{Pop} \text{happiness} \cdot \text{political power}}{ \sum_{}^\text{Pop} \text{political power}}$

Note: Pop drones with the Rogue Servitor civic act like they have political power = 0.09 and Bio-Trophy pops have political power = 1 (only for the purpose of this formula).

Approval rating ranges from 0% to 100% and has a base level of 50%.

Each point of approval rating above 50% adds +0.6 stability, up to +30 stability at 100% approval rating.
Each point of approval rating below 50% adds −1 stability, up to −50 stability at 0% approval rating.

Upkeep[]

Upkeep of a pop heavily depends on the type of pop and the type of empire. Usually it consists of:

Base upkeep – some basic resource for the pop to sustain itself
Living Standards upkeep – an amount of consumer goods
Job upkeep – additional resources needed for the pop to perform its job
Housing needs – a planet wide resource for pops to live in
Amenities needs – a planet wide resource for pops to be happy about

Colony habitability lower than 100% for specific pop leads to penalties in the form of increased pop base upkeep and amenities needed for that pop.

See also: Colonization#Habitability

Base upkeep[]

Base upkeep is always 1 of a basic resource per month, which depends on the type of pop and possibly its traits. Biological pops consume food, while Lithoid pops consume minerals; Mechanical pops ( Robot and Machine) consume energy. Certain species traits can replace part or all of a biological species' base upkeep with energy as well. Fungoid or Plantoid pops with the Phototrophic trait replace half their base upkeep with energy upkeep. As do pops with the Radiotrophic trait, with the addition that they require no energy upkeep when living on a Tomb World. Voidling replaces all of a pop's base upkeep with energy upkeep. Exotic Metabolism adds 0.125 exotic gases upkeep and Cyborg traits add additional energy upkeep.

After base upkeep is determined, it can be modified by species, planet, or empire modifiers. For example, Zombie pops have −100% base upkeep. Although there is a hidden cap of −90% for the sum of modified applied, this makes base upkeep always non-zero. ^[1]

Note: Organic pops includes Biological and Lithoid pops.

**Base upkeep**
Pop type	Base	Phototrophic	Radiotrophic	Radiotrophic	Voidling
Biological	1.0 food	0.5 food 0.5 energy	0.5 food 0.5 energy	0.5 food	1.0 energy
Lithoid	1.0 minerals		0.5 minerals 0.5 energy	0.5 minerals	1.0 energy
Mechanical	1.0 energy

Living standards upkeep[]

See also: Living standards

In addition to base upkeep, non-Gestalt pops, including Bio-Trophies, require a certain amount of consumer goods based on their living standards. Synthetic ( Mechanical) pops that are given citizen rights require consumer goods as well. The amount of consumer goods typically depends on the pop's stratum, but other modifiers can increase or decrease this amount.

Housing[]

Housing represents the living space available for pops to live comfortably. Housing is primarily provided by districts, with city districts giving more housing than their resource-focused alternatives. Each pop requires 1 unit of housing by default but the housing demands of individual pops can change due to a variety of factors. If the number of pops exceeds the amount of housing it will cause stability to drop by $40 \cdot \frac{\text{missing housing}}{\text{total housing required}}$ and a flat +50 planet emigration push.

As a rule of thumb, each resource district exactly pays for itself in terms of housing, while the pops that work building jobs need city districts (or housing buildings) for their housing, though the capital building provides some buffer before cities are needed. This applies equally to Ecumenopolises. The Agrarian Idyll civic gives extra housing to resource districts, allowing the empire to house its pops working building jobs mostly via resource districts. The Trans-Stellar Corporations tradition adds jobs to habitat trade districts, but does not match them with additional housing, making some residential districts necessary.

Amenities[]

Amenities represent the infrastructure and jobs dedicated to fulfilling the needs of the population on a given colony. Individualist empires obtain amenities from a variety of jobs while Gestalt Consciousness empires obtain them primarily from Maintenance Drone jobs. High amenities grant increased happiness to citizen pops in regular empires and increased stability in Gestalt Consciousness empires, while insufficient amenities will lower pops' happiness (or stability, for Gestalts) on the colony.

Pops have a base amenity requirement of 1 Amenities, slaves require 0.75, and non-citizen Robots require 0.5. The shown amenities value is the available amenities value, or the surplus. After base amenities upkeep is determined, it can be modified by species, planet, or empire modifiers. 5 Amenities are always lost on every colony due to inefficiencies. The formula for available amenities (or extra amenities) is the following:

$\text{Available Amenities} = \text{Amenities Provided} - (5 + \text{Pop Amenities Usage}) =$

$= (\text{Amenities Provided by Buildings} + (\text{Amenities Provided by Jobs} \cdot \sum \text{modifiers with Job scope})) \cdot \sum \text{modifiers with Planet/Empire scope} -$

$- (5 + \text{Pop base Amenities Upkeep} \cdot \sum \text{upkeep modifiers})$

One impactful upkeep modifier is the effect of subprime habitability on the specific pop.

Most values representing amenities are rounded to the closest integer value (the tie-breaking rule is unknown), except for amenities from pop jobs - it is rounded down.

The formula for available amenities or amenities deficit effect on a planet's happiness ( stability for Gestalt empires) is not strictly linear, with less effect for extra amenities than missing amenities.^[2]

The formula for extra amenities (available amenities > 0 case) contributing to happiness is:

$\text{happiness bonus} = \text{min} \left( 20\%, \frac{20 \cdot \left\lfloor \text{available amenities} \right\rfloor}{\left\lfloor \text{pop amenities usage} \right\rfloor} \right)$

In other words, it scales from +0% with 0 available amenities, to +20% with twice as many available amenities as necessary.

The formula for a amenities deficit (available amenities < 0 case) affecting happiness is:

$\text{happiness penalty} = \text{max} \left( -50\%, \frac{200/3 \cdot \left\lfloor \text{available amenities} \right\rfloor}{\left\lfloor \text{pop amenities usage} \right\rfloor} \right)$

In other words, it scales from +0% with 0 available amenities, to −50% when the planet has less than 25% of amenities needed.

Note: for readability reasons in the formulas above for the happiness effect as a function of amenities the rounding operations are noted as rounding down when in reality rounding to the nearest integer is used. The stability bonus or penalty received by Gestalt Consciousness empires from amenities in a colony by value is the same %-value a non-Gestalt empire gets in happiness (the formulas above can be used).

Amenities can be affected on an empire-wide basis by the following:

Source	Amenities
Artificial Moral Codes technology	+5%
Executive Retreat branch office building	+10%
Resort World	+15%
Profane Consecrated World	+1%
Respected Consecrated World	+2%
Venerated Consecrated World	+3%
Holy World Consecrated World	+4%
Mega Art Installation (stage I)	+5%
Mega Art Installation (stage II)	+10%
Mega Art Installation (completed)	+15%
Mega Art Installation (perfection)	+20%
Vultaum Star Assembly secrets special project	+20%

Source	Amenities usage
One Vision ascension perk	−10%
Vultaum Reality Perforator relic	−10%
Ecological Protection resolution 2	−5%
Discourage Planetary Growth decision	+25%
Resident citizenship status	−25%
Ascetic	−15%

Stratum[]

Strata represent pops' social classes. The higher a pop's stratum, the more political power they have and the more consumer goods they require for upkeep, according to their living standard. It also determines the resettlement cost. Resettlement costs no unity if the empire has the Corvée System, Subsumed Will, or OTA Updates civic, or if the pop is enslaved or a non-sentient robot.

If a pop takes a job above its stratum, it will be promoted to the higher stratum. If there are no available jobs of equal or higher stratum the pop will become unemployed, slowly demoting in stratum and causing happiness penalties in most living standards. The Shared Burdens civic and living standards each reduce demotion time by −45%, the Kinship tradition reduces it by −75%, and being in default reduces it by −50%. Slaves demote instantly, regardless of stratum.

Stratum	Rank	Demotion time	Requirements	Output modifiers
Ruler	3	1800	Gestalt Consciousness	Modifiers0 +40% Clone Soldier Ascendant trait +10% Shadow Council civic +5% Necrophage trait
Specialist	2	900	Gestalt Consciousness	Modifiers0 +25% Clone Soldier Ascendant trait +10% Meritocracy civic +10% Fanatic Egalitarian ethic +10% Academic Privilege living standards +5% Egalitarian ethic +5% Necrophage trait +5% Pursuit of Profit/Creative Collectives tradition
Worker	1	N/A	Gestalt Consciousness	Modifiers0 +10% Fanatic Authoritarian ethic +5% Authoritarian ethic +5% Workplace Motivators tradition +10% Rural World designation +5% Very Strong species trait +2.5% Strong species trait +2.5% Industrial Development resolution 1 +5% Industrial Development resolution 2 +7.5% Industrial Development resolution 3 +10% Industrial Development resolution 4 −2.5% Weak species trait −10% Necrophage trait
Complex Drone	0	Instant	Gestalt Consciousness	Modifiers0 +20% Manufacturing Focus production policy +5% Machine Capital designation +5% Nest Planet designation +5% Machine Nexus designation +5% Peak Performance/Neural Signal Boosters tradition +1% per Bio-trophy "employed" on planet −20% Extraction Focus production policy
Menial Drone	0	N/A	Gestalt Consciousness	Modifiers0 +20% Extraction Focus production policy +10% Fringe Planet designation +5% Machine Capital designation +5% Hive World designation +5% Machine World designation +5% iconify domination tradition −20% Manufacturing Focus production policy
Bio-Trophy	0	N/A	Organic species in a Rogue Servitor empire	Modifiers0 +10% Send Artifacts to Organic Sanctuaries decision
Undesirable	0	N/A	Undesirables citizenship
Assimilation	0	N/A	Assimilation citizenship
Criminal	1	Instant	High crime
Deviant Drone	2	Instant	High deviancy in Hive Mind empires
Corrupt Drone	2	Instant	High deviancy in Machine Intelligence empires
Pre-sapient	0	N/A	Pre-sapients
Precursor	3	5	Fallen Empire
Primitive	0	N/A	Alien pops on The Preserve

Slavery[]

Entire species can be enslaved by giving them a certain citizenship, which opens a new tab in the Species Rights menu called Slavery Type that determines what are the effects of slavery.

Citizenship	Slavery requirements	Notes
Slaves	Species is alien and the empire is Authoritarian, Xenophobe, or Gestalt Consciousness
Servitude	Species is robot and the empire has the Servitude Artificial Intelligence policy	If Synthetic Dawn is active, setting this may cause a robot uprising.
Any	Slaver Guilds or Indentured Assets civics	Up to 35% of the pops are enslaved if the world does not have enough pops with the Slaves or Servitude citizenship

Enslaved pops also use only 0.75 amenities and 0.75 housing (instead of 1), which can be further reduced if the slavery type is Servitude or Livestock. They also have a resettlement cost of just 50 energy. Enslaved pops cannot join factions and have only 25% political power, or 18.7% if a Slave Processing Facility is present on the planet. However, they can still increase crime if they're too unhappy.

Low stability is more dangerous when enslaved pops are present on a planet. Normally dangerous events can only occur if it's lower than 25, but if any pop is enslaved it should be kept above 40.

Slaves, workers and specialists[]

In addition to the slave resource output modifiers, worker resource output modifiers can also affect slaves in worker jobs. As of 3.0.1, slaves in specialist jobs are affected by specialist output modifiers, but not by slave resource output modifiers, if in Indentured Servitude.

Slaves working on miner jobs can benefit from worker resource output modifiers, such as Authoritarian and Strong.

If a modifier affects the resource output of both workers and slaves, it actually affects slaves in worker jobs twice.

The Extended Shifts edict increases slaves resource output by +10% and workers resource output by +10%, resulting in an total +20% bonus to slaves in worker jobs.

Modifiers that affect workers aside from the resource output ones don't affect slaves.

The Extended Shifts edict decreases slaves' happiness by −10% and worker happiness by −10%. It does not cause the slaves to suffer −20% happiness.

Ethics attraction modifiers[]

Ethics divergence is where a pop or group of pops decide to follow a different ethic than the general population. A materialist pop may decide to follow a more spiritual path and a pacifist culture might decide that peace is the path of the weak.

Each pop in an empire will only embrace a single, non-fanatic ethic. At the start of the game, the population will be made of the empire's governing ethics. As population expands and eventually is divided over various planets and sectors, certain segments may decide to adopt values that are different from the core values of the species due to various circumstances in and around the empire.

Each ethic has a certain attraction value attached for all pops, depending on both the empire's situation and their own. Each pop can only switch ethics once per year. The exact values and options that influence the attraction levels of certain ethics can be found at Ethics attraction. The attraction factors of ethics can be amplified by certain circumstances such as policies or traits.

Having a positive ethics attraction effect will let all actions that increase attraction to the government ethics result in even more attraction, and negative amounts will be decreased. With a modifier of 50%, an action that would increase attraction by 2 would instead increase by 3.

Hovering over a pop's ethic will display the attraction towards all ethics.

Robots[]

Sentient Robot — Sentient humanoid robot

Robots are artificial pops and can be constructed once the required technology becomes available. They have the Mechanical trait, giving them +200% habitability on any planet. Robots can be given new traits via robo-modding, and the species template with the highest number of used trait points will be built by default. A different template can be specified for each planet.

The jobs a robot can have are limited by the highest robot technology researched. If an empire researches the Synthetics technology with AI policy set to Servitude or Citizen Rights, all robots immediately become sapient, gain ethics, are affected by empire and planetary happiness modifiers and contribute to crime. With Citizen Rights they also become affected by all happiness modifiers.

Tech level	Maximum stratum	Sapient
Robotic Workers	Worker
Droids	Specialist (except Researcher, Bureaucrat and Culture Worker) if AI policy is set to Outlawed
Synthetics	Ruler if AI policy is set to Citizen Rights Specialist if AI policy is set to Servitude Specialist (except Researcher, Bureaucrat and Culture Worker) if AI policy is set to Outlawed	if AI policy is set to Outlawed if AI policy is set to Servitude or Citizen Rights

Robots without Citizen Rights require 50% less housing and amenities and do not need consumer goods. If a planet with sapient robots is captured by an empire that doesn't have the Synthetics technology, they lose their sapience, and if a planet with non-sapient robots is captured by an empire that has the Synthetics technology and does not have the Outlawed Artificial Intelligence policy, they are immediately given sapience. Note that non-sapient robots can do all specialist jobs with Droids tech, but not after researching Synthetics tech.

It's possible to take the Synthetic Evolution ascension perk and turn all organic pops and leaders into synthetics.
Hive Mind empires cannot build robots and will always purge all robots on their worlds.

As long as an empire has the Artificial Intelligence policy set to Servitude there is a risk of them starting an AI rebellion, if either the Synthetics or Sapient Combat Simulations techs have been researched.
Machine Intelligence empires cannot build robots, but they can use them as drones if conquered from a regular empire or bought on the slave market. Robots in a Machine Intelligence empire can work all jobs and are not affected by happiness.

Purges[]

Purges represent the systematic elimination of specific pops or entire species from an empire and can be done on a per pop or species basis.

Targeted pop purging still requires applying the species-wide slavery at minimum and it is limited to a basic extermination, although without production penalty. Gestalt Consciousness empires can purge their pops of any composition freely, with exception of Bio-Trophies.

Species-wide purging is done by setting the species' citizenship to Undesirables. Gestalt Consciousness pops in empires of different authority are forced to be set as Undesirables, unless they can be assimilated. Therefore, gaining planets from a Gestalt Consciousness empire means that the planet will be lost when it is empty of the conquered pops if there is not at least one non-gestalt pop on it. There are also four special cases:

Pre-sapients can only be purged if the Pre-Sapients policy is not set to Protected and they are automatically purged if it's set to Extermination.
Robots are automatically purged if the Robotic Workers policy is set to Outlawed.
Synthetics can only be purged if the Artificial Intelligence policy is not set to Citizen Rights.
Empires with the Evolutionary Mastery ascension perk can change the citizenship of hive mind pops to Assimilation, which prevents them from being purged.

Fallen and Awakened Empires can choose not to purge Hive-Minded/Machine pops.

Having any species-wide purge is a negative issue for Xenophile factions, aside from the case of Gestalt Consciousness pops and outlawed robots.

There are multiple types of purge available, determined by the Purge Type species rights.

Type	Monthly decline	Effects	Loss	Refugees chance	Requirements	Description
Displacement	25	−30% Happiness −50% Pop housing usage	no	100%	Not Genocidal empire Not Hive-Minded or Machine species Not Cybernetic species if empire is Driven Assimilator Not Mechanical species, unless the pops are sapient	It's not that we drive them from their homes. Their homes are simply no longer theirs.
Extermination	100	−1000% Happiness	yes	5%	Not Devouring Swarm or Terravore Mechanical species or Purge policy is Allowed	The extermination squads are efficient. The dissolution of entire populations naturally takes time, but they get the job done.
Neutering	10	−20% Happiness	no	0%	Not Gestalt Consciousness Not Hive-Minded or Machine species Not Mechanical species, unless the pops are sapient	Think of it as a phasing-out of a people. Our nation goes to meet the future, only some will not be with us.
Forced Labor	50	−1000% Happiness +3 Food +3 Minerals	yes	25%	Not Gestalt Consciousness Not Hive-Minded or Machine species	With this final sacrifice, they will at least have been of some use.
Processing	50	−1000% Happiness +6 Food if species is biological +4 Minerals if species is Lithoid +3 Alloys if species is Robotic	yes	20%	Machine Intelligence Not Robotic species Hive-Minded species unless empire is Devouring Swarm or Terravore	It is a sad but inescapable fact that some are destined to simply fuel the ambitions of their betters.
Chemical Processing	50	−1000% Happiness +6 Energy	yes	20%	Machine Intelligence Not Robotic species	They will soon attain a more efficient form.
Necrophage	20	−50% Happiness Purged Pops are changed to primary species	yes	25%	Necrophage origin Purge policy is Allowed Not Robotic species	Only the strongest may survive in a hostile galaxy. This way their journey may continue.

Refugees[]

Pops from other empires may flee to escape purges, slavery, resettlement, crisis bombardment, or as a result of land appropriation. Whether another empire is willing to accept those fleeing depends on its Refugees policy. Refugees will not head for empires where they have the Undesirables citizenship. Accepted refugee pops will get +20 happiness for 10 years.

Once refugees are generated they will head for any empire that will accept them with their Refugees policy following the following order:

Habitability at least 70% and housing at least 1
Habitability at least 70%
Habitability at least 50% and housing at least 1
Habitability at least 50%
Habitability at least 20% and housing at least 1
Habitability at least 20%
Housing at least 1
Any other planet

Pops that are robotic or have the Hive-Minded, Nerve Stapled or Zombie traits cannot become refugees.

References[]

↑ from the patch 3.7 notes: Capped resource upkeep/cost/production reduction modifiers to -90% for any given case. I.e. you will no longer be able to have completely free upkeep on jobs which are meant to cost upkeep.
↑ The effects are set in 00_static_modifiers.txt at planet_amenities_high, planet_amenities_low, planet_amenities_no_happiness_high, and planet_amenities_no_happiness_low; the threshold for maximum effect is set in 00_defines.txt at MAX_PLANET_AMENITIES and MIN_PLANET_AMENITIES.