Which Android version introduced adoptable storage?

Android 6.0 introduced adoptable storage.

Known as Marshmallow, Android 6.0 added adoptable storage, allowing a compatible microSD card to be formatted and treated as an extension of a device’s internal storage. Instead of remaining merely portable storage for photos and files, the card could hold applications and private app data alongside the phone’s built-in storage.

Adoption came with important trade-offs. Android encrypted the adopted card and tied it to the device, so removing it could make apps and data unavailable. The card generally could not be moved to another phone and used normally without reformatting it. Users therefore had to balance extra capacity against portability and the reliability of removable flash media.

This feature is often confused with Android 5.0’s broader improvements to memory-card access through the Storage Access Framework. Those changes improved how apps could write to external storage, but they did not make an SD card function as internal storage. Adoptable storage was specifically associated with Android 6.0, and some manufacturers, including Samsung and LG on certain devices, chose not to enable it.