Here is the full list of all 20 STAY achievements.
The base game contains 12 achievements, and there is 1 DLC pack containing 8 achievements.
Complete 200 Tasks in total
Survive for 1 Hour in a single Core test
Survive for 10 Minutes in a single Core test
Complete 50 Tasks in total
Complete 100 Tasks in total
Farewell
Survive for 5 Minutes in a single Core test
Survive for 2 Minutes in a single Core test
Complete 30 Tasks in a single test
Complete 10 Tasks in a single test
Commit an Error for your first time
Complete a Task for your first time
Survive for 15 Minutes in a single Lethal test
Unlock all the other achievements
Survive for 5 Minutes in a single Lethal test
Complete the Phase 10 on a single Wave test
Complete the Phase 5 on a single Wave test
Complete a Speedrun test in less than 5 Minutes
Complete a Speedrun test in less than 8 Minutes
Switch to a different Color