RuneLite HD was set to be released on September 6th, but the creators of the mod, who spent 2000 hours over 2 years on the project, were contacted by Jagex and asked to shut down the project “at the eleventh hour” according to the creators. The reason behind this seems to be that Jagex is working on its own HD upgrade for OSRS.
Yesterday, September 6, 2021, RuneLite HD would have been released. The code had been reviewed and bugs had been fixed – it was ready to go. You would have been playing with it right now. Yet, at the eleventh hour, Jagex contacted me asking me to take it down in light of the reveal that they have a similarly-themed graphical improvement project that is “relatively early in the exploration stages”.
Jagex has since then posted an official statement on the subject of Third-Party HD Clients.
*Update
After listening to feedback from the OSRS community, Jagex released a statement on Twitter saying they are having conversations with the creator of Runelite HD.