We will be making the current weekly version the new quarterly version on or shortly after November 17th, 2020. The versions will then be:
3.40 will be retired.
If you don't specify a version (or request a retired version), you will be served a default version, which depending on your key configuration will be either 3.42 or 3.43. But a developer specified version will always be honored and served when requested when it's an existing version.
To report issues with any version of the API, see:https://issuetracker.google.com/savedsearches/558438