Every time you upload a new version of a file, Cloud can keep the one it replaced.
How many versions you keep
A count, not an age. “The last 10” is a promise you can hold in your head; “90 days” turns
into an unpredictable number of gigabytes.On Free, “1” means exactly the behaviour before history existed — the current version and nothing
else. A free account sees no change and pays no storage for a feature it does not have.
Using it
Open a file’s version list to see previous revisions with their dates and sizes. From there you
can:
- Restore a version, making it current again. The version it replaces becomes a previous
version in turn, so restoring is not destructive.
- Delete a single version, if it is taking up space you would rather use.
Storage
Versions count against your quota, like anything else you store, and the storage panel breaks
out how much of your usage is history — a number that appears in your usage should be one you can
see.
When a file exceeds your plan’s version count, the oldest kept version is discarded to make room.
If a large file is version-heavy — a course package you re-export daily, say — delete the
intermediate versions you do not need rather than letting them consume your allowance.
Encryption
Versions are encrypted exactly like current files, under the same folder key chain. Each version
gets its own randomly generated base for its chunk encryption, and every chunk is bound to the
version it belongs to — so a chunk from one version cannot be substituted into another, even by
someone holding your storage.
Restoring a version is a metadata change: nothing is re-encrypted and nothing is re-uploaded. 
