We are happy to announce the opam 2.0.0 final release candidate. Hooray! 
It will be promoted to 2.0.0 proper within a few weeks, when the official repository format switches from 1.2.0 to 2.0.0.
You’ll find all information about opam update & repository upgrade in this blog post.
Big thanks to all who helped test and polish the release!
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I maintain the opam package in MacPorts (which is useful for people bootstrapping their OCaml setup.) When should I upgrade the package?
I think the best is to have the official opam2.0.0 released to update opam os packages. In that way, the opam repository will already be switched to the 2.0.0 format.
The roadmap is detailed in this blog post.
My read of the sequence of events suggests to me that OS package maintainers should probably take OPAM 2.0 before the upgrade of the opam.ocaml.org repository on September 17th. Would it not be a good idea to shake out the opam command upgrade for a bit before upgrading the official repository from 1.2 to 2.0?