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did I understand it correctly that tor 0.2.8.x did not make it into OpenBSD 6.0 because tor 0.2.8.x has been released to recently?

Correct, it's at 0.2.7.6p1.

There are ways of checking this, such as simply looking at a mirror's package list:

http://openbsd.mirrors.pair.com/6.0/packages/amd64/

yes, that is how I determined that there is no tor 0.2.8.x in OpenBSD 6.0 ;)

(I just wanted to confirm the reason for this from the maintainer, but OK)