Echo is a tactical stealth game, employing many of the traditional mechanics and conventions of the stealth genre, with the addition of a learning AI that allows the player's opponents to learn from and mimic their behaviour.
The gameplay takes place inside a labyrinthine planet-spanning palace, patrolled by clones of the protagonist and player-character, En. The clones will pursue and attack En on sight. The player must use a combination of avoidance, distraction, and combat to evade the clones and progress deeper into the palace towards the final goal.
The palace is controlled by an intelligent system that monitors En's behaviour and periodically reprograms the clones to better mimic her. As the player proceeds, actions such as crouching, running, leaping, firing En's weapon, etc. will be recorded by the palace system. Once En's behaviour has diverged significantly from the current programming of her clones, the palace "reboots" and the clones will gain the ability to behave in the recorded ways. For example, if En kills a clone by shooting it with her gun then it is highly likely that after the next reboot cycle the clones will attempt to shoot her if they spot her.
The palace reboots in two phases. In the first phase of the reboot, all the lights in the environment switch off and the palace system stops monitoring En's actions for a period of about thirty seconds. The lack of light severely limits the player's situational awareness but grants a window of time to act unmonitored, which can be used for tactical advantage by waiting to perform actions during this phase that the player does not want the clones to learn. The second phase of the reboot is a hard cut to black, after which the lights switch back on, the clones' alert state resets and they revert to their pre-programmed patrol patterns. The clones will now begin to mimic the behaviours learned from En during the previous cycle of monitoring.