@MikeT and Co,
Tag auto-completion is functional in the edit pane of an item, but it doesn't appear to be available when attempting to add a tag to a selected item(s) via the right-click menu. I'm wondering if you plan on addressing that at some point, hopefully soon?
Thanks for your consideration, and for continuing to develop an already-great product,
(1Password for Windows v 7.3.684)