Quote Originally Posted by PC Gamer
At the beginning of March, Github user tostercx, who also goes by t0st, claimed they'd discovered a way to reduce GTA Online's loading times by up to 70 percent. Further, they also released a fix that you can pick up here—with a caveat that it's an unsupported "proof of concept, not for casual use.”

For those interested in the technical angles of such things, tostercx also wrote up a detailed analysis of what was wrong, and how they’d fixed it. It's fairly technical, but the short version is that the slowdown was being caused by "a single thread CPU bottleneck while starting up GTA Online,” a problem they estimated "shouldn’t take more than a day for a single dev to solve."

It actually took a somewhat longer than that, but Rockstar has confirmed that tostercx's findings were accurate, and that a fix is on the way.

"After a thorough investigation, we can confirm that player t0st did, in fact, reveal an aspect of the game code related to load times for the PC version of GTA Online that could be improved," the company said in a statement. "As a result of these investigations, we have made some changes that will be implemented in a forthcoming title update."

Rockstar didn't say when the fix might become available, nor did it confirm t0st's estimation of a 70 percent reduction in load times. It did confirm that the company has been in touch with t0st, however, "and would like to thank him again for his efforts."
Rockstar thanks GTA Online player who fixed poor load times, official update coming | PC Gamer