Stackdriver/Google Cloud monitoring is backed by Monarch, so if you want the flavor of a Monarch distribution-valued metric, see the docs:

https://cloud.google.com/monitoring/api/ref_v3/rest/v3/Typed...

Since the distribution is represented by a CDF of buckets, there's no guarantee that you'll get an accurate representation of the median or any other quantile. On the other hand you'll get an exact average.