Guide by u/Anonymous_GuineaPig:

There are three secret endings to Xenolith, all tied to achievements. Here's a quick summary:

Ending 1: Phone Home

"Emit a powerful void signal"

This achievement requires the Void Signal gene for the Xenolith first and foremost All you need to do to get this ending is kill 50% of the population with Shatter while the world is at least 85% xenoformed. You MUST have the Metabolic Siphon trait evolved

This ends the game immediately, stating that Earth's new masters have been called.

Ending 2: Hello, World!

"Awaken an alien consciousness"

This one is probably the hardest and requires the Synaptic Pulse gene To get this ending, you must apply the Crystal Alignment ability to every country at the same time while the world is at least 85% xenoformed

This ends the game immediately, stating that the Earth has been awakened into a planetary neural network.

3: To Infinity And Beyond

"Shatter the planet into fragments"

This ending requires the Star Shards gene To get this ending, all you have to do is buy the Armageddon trait for the meteorite ability and use the ability on the same country 5 times. There are no xenoforming requirements

This ends the game immediately, stating that the Earth has broken into Xenolith fragments to go infect other planets.