Supporting Python 3 means supporting Python 3 up to the current point release.
Python point releases are backward compatible. What works on 3.0 should generally work on 3.4. See PEP 387 for the general guidelines on this policy. Python 3.4 added some deprecations but none of these will affect packages that were once only written for 3.0, at least until Python 3.5 or 3.6 are released.
Exceptions are more easily made for C extensions. Python 3.3 saw a new internal Unicode format, but support for the old Unicode C APIs is still present in 3.4.
The 3.4 deprecations are for the most part for code that has been extremely rarely used, if at all. Any code that uses features that are now slated for removal should trigger warning messages.
For future Python 3.x releases, just download the package and use it. If anything were to break, look through the Deprecated entries in recent Python 3 release notes to see if the project may have been using a feature since removed.
In any case, try and check the project documentation; a good project will list exact versions on which they have tested the package. The requests project states:
Requests officially supports Python 2.7 & 3.4–3.7, and runs great on PyPy.
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solved What does “Supports python 3” mean? [closed]