It’s BSL so I guess open source but not “free software”?
Edit: okay as has been widely pointed out this is not an open source license. The text of the license says this. They have updated the post to (kind of) acknowledge this. They also state that this non-open source license “aligns strongly with our own open source goals and intent for Codecov at this time”, really committing to try to confuse whether or not they’re open source