CIRCLE_TAG is empty

Build Environment
1

I’m using 2.0 with a filter on tag.
filters:
tags:
only: /[0-9]+(.[0-9]+)*/
I can see that my commit has a tag and that the job is run. However the variable CIRCLE_TAG is empty.

2

It’s not empty, I just realised it’s either CIRCLE_BRANCH or CIRCLE_TAG…