Action cost

Most actions you take in the game have an action cost. This determines how long it takes you to perform the action.

The standard action cost representing a "one-turn" action is 1,000. Quickness determines how many action points a character has available to spend each turn, which is typically also 1,000.

All action costs are randomly varied by up to ±10% in order to make the initiative order of the game less deterministic.

The most common action cost besides 1,000 is 100, "one tenth of a turn" or "one segment". Directing companions has this action cost, as do various cases of flipping power switches.

Action Cost Modifiers

This section is an excerpt from Quickness#Action Cost Modifiers.

These things modify the action cost of certain actions, allowing a character with the same quickness to perform more or less of those actions.

Name	Type	Action Cost Effect
bounding boots	equipment	33% additional reduced action cost of sprinting while worn. (you sprint at 3 times your normal movement speed instead of 2 times your normal speed)
Empty the Clips	skill	50% temporary reduced action cost of firing pistols for twenty rounds.
Fastest Gun in the Rust	skill	25% permanent reduced action cost of firing pistols.
medassist module	cybernetic	80% reduced action cost of applying any tonic. Pre-loaded injectors are applied by the medassist module at no action cost.
micromanipulator array	cybernetic	40% reduced action cost of Tinkering skills.
plastifer chem vest	equipment	100% reduced action cost of applying any tonic.
rapid release finger flexors	cybernetic	25% reduced action cost of firing pistols.
Short Blade Expertise	skill	25% reduced action cost of bump-attacking while primary hand contains a short blade. Also applies to using the Hobble skill or the Shank skill with a short blade in your primary weapon hand.
Sprinting	ability	50% temporary reduced action cost of movement.
steel butcher knife	equipment	variable reduced action cost of the Butchery skill (the action cost to butcher a corpse is divided by 1 plus the number of steel butcher knives currently equipped).
Swimming (the action)	environmental	+500 temporary action cost to movement while moving through any large pool of liquid.
Swimming (the skill)	skill	50% permanent reduced action cost of swimming. (swimming costs only 250 extra action points, instead of 500 extra action points)
Telepathy	mental mutation	90% reduced action cost of directing companions to perform tasks.
Two-headed	physical mutation	20% or greater permanent reduced action cost of using mental mutations, depending on mutation level.

In addition, Movement Speed affects the action cost of a creature's basic movement action.

Notes

Modding note: at an internal technical level, this concept is referred to as "energy". "Action cost" is used in public facing materials to avoid confusion with things one thinks of first when thinking "energy".