Hi everyone,
The QIIME 2 development team would like to thank everyone for their help this last week identifying when our release instructions were broken, usually a dependency returning 404. We really appreciate your patience as we rebuilt our install files to fix these issues.
As a direct result, we’ve retooled how we distribute these conda environments to prevent these issues from occurring in the future.
Instead of QIIME 2 using what we call an explicit environment file we’re switching to the more modern yaml environment file. The net impact is we will no longer be using very specific builds/URLs. This means that you shouldn’t see 404s while conda downloads QIIME 2’s dependencies if something changes.
Starting with 2017.12, we’ve updated our install instructions, which can be found here.
As an additional upside to these changes, we can now use the latest conda (4.4) once more! 
Before and After
Where you would have typed:
conda create -n qiime2-RELEASE --file https://URL-WE-PROVIDE
You would now type:
wget https://URL-WE-PROVIDE/RELEASE-NAME.yml # or your favorite tool
conda env create -n qiime2-RELEASE --file RELEASE-NAME.yml
That yaml file (RELEASE-NAME.yml) can be deleted once the environment has been created.
For developers (or advanced users of conda) who are used to using:
conda install --file https://URL-WE-PROVIDE
within an existing environment, you should now use
conda env update --file RELEASE-NAME.yml
to accomplish the same task with the new yaml environment file.
As always, thanks for supporting QIIME 2!