We'd like to apologise for the delay in returning tag filtering. We had hoped to have tag filtering updated, run through our testers, and back out to you by the end of July. However, it's taking us much longer than we expected to finish that code and get it all tested. We hope to have all the work finished and the tag filters returned by the end of September. However, we can't promise we won't run into more unexpected snags, so right now this is a very rough timetable and we may have to revise it. We'll keep people updated as the work progresses.
We've been able to tackle a lot of other performance-related issues since the problems started in May/June. However, sadly this isn't enough to allow us to restore the old filter code, which just isn't able to cope with the number of users the site has now. It's been necessary to completely remove the old filter code and rewrite it from the ground up, which is a major piece of coding.
We already knew that this code was nearing breaking point and were actively working on new tag filters before the performance problems hit, which is why we were optimistic about introducing the new tag filters quickly. However, coding is always an uncertain business, and it's taken longer than we expected to finish the new code. In writing a big piece of functionality like this, it's not too unusual to run up against challenges while coding that you didn't anticipate up front. In addition, we only have a limited number of coders who are able to take on something this complex: the coder who is taking the lead on this project has been working on it all available hours, but sadly we've yet to figure out how to clone her.
In the meantime, if you've not already seen the Disabling filters: information and search tips post, check it out for alternate ways of finding works on the Archive.
Once again, many apologies for the inconvenience. We thank you for your patience while we work hard to bring back tag filtering!