Is it okay to have both versions imported in the same project? Are they namespaced separately?

Or do we need a completely new submodule 'hystrix-yammer-metrics3-publisher'?

And what is the "official" GroupID since there is both 'com.yammer' and 'com.codahale'. Version 2 was 'com.yammer', this adds version 3 using 'com.codahale'. Both are available on Maven Central: http://search.maven.org/#search%7Cga%7C1%7Cmetrics-core