Originally ElfHosted Aarr stacks used RDTClient exclusively, until "West's blackhole" scripts were introduced. Blackhole offered the unique feature of only downloading cached content, and immediately failing on uncached content, the better to prevent your RD library from getting "clogged up" trying to download items with low seeders, etc.
A few months ago, we introduced Decypharr, an evolution of "Cypher's blackhole", which added a web UI, and critically, WebDAV support, so that the whole download-and-symlink-file process was fully self-contained (as opposed to relying on refreshing the Zurg WebDAV mount).
It's been in trial for a few months, and has been the default on fresh installs since then. Now that Decypharr has now hit v1.0.0 (stable), we've elected to deprecate RDTClient and Blackhole bundling in our stacks by default, from 1 June 2025. While you can still add them to your stack if you prefer, we believe that you'll get the best possible experience currently by switching over to Decypharr, if you haven't done so already.
See the documentation for configuring Decypharr for further details.