Hi @Mehrbod_Estaki regarding this post: V3-V4 99 greengenes feature classifier](How to obtain an updated V3-V4 99 greengenes feature classifier - #2 by Mehrbod_Estaki):

Could you please provide another one (like the one you provided:Dropbox - v3v4-99-gg-nb-classifier.qza - Simplify your life) please for version 2021.8? thanks
Is it better to have to be v3-v4 rather than running it on the whole greengenes regions?

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Hi @MarwaTawfik,
Using a region specific classifier has been shown to improve classification accuracy by a bit, so I would recommend using this approach if you can. If you can't access resources to train your own classifier, then using the full length classifier is not that much less accurate either, and pre-trained classifiers are already available on the q2 resource page.
As for providing a new classifier, I haven't had to use those specific primers in some time so I haven't had the need to produce an updated classifier, and not sure when I'll get a chance to do it, however, since this is based on the Greengenes database, most local machines should be able to handle it. You can try training your own using the instructions here, which is what I used initially, or you can also use the RESCRIPt plugin also which has a lot more functionalities.