The $10,000 Bug: How One Developer Fixed GTA Online's 6-Minute Loading Screen

In early 2021, GTA Online players had grown painfully familiar with staring at loading screens for up to 6 minutes. While story mode loaded in about 70 seconds on the same hardware, online mode seemed stuck in molasses. Developer t0st decided to investigate—and uncovered performance disasters that Rockstar had shipped for years.

The Investigation

t0st started with basic profiling. Task Manager showed one CPU core maxed out at 100% while disk, GPU, and network sat idle. Using Luke Stackwalker, a stack sampling profiler, they identified the bottleneck: a single function eating most of the CPU time.

The next step required reverse engineering. Using IDA Pro and x64dbg to disassemble and debug the running game, t0st discovered the game was parsing a 10MB JSON file containing roughly 63,000 items for the in-game shop catalog. But the implementation had catastrophic flaws.

The Culprits

Two critical bugs emerged:

Inefficient JSON Parsing The JSON parser repeatedly called strlen on the same long strings without caching results. Since strlen scans the entire string every time, this created massive overhead when processing thousands of JSON entries.

O(n²) Duplicate Detection After parsing each of the ~63,000 items, the code performed a linear search through the entire existing array to check for duplicates before insertion. With all entries being unique, this meant roughly 2 billion unnecessary string comparisons. The developers had used an array instead of a hash map—a textbook performance antipattern.

The Fix

t0st created a proof-of-concept DLL that hooked into the game process:

Cached strlen results for repeated calls on the same strings
Bypassed the duplicate checking entirely (since the data had no duplicates anyway)

The Results

The improvements were dramatic:

Original loading time: ~6 minutes
With duplicate check bypass only: 4 minutes 30 seconds (25% improvement)
With JSON parser fix only: 2 minutes 50 seconds (53% improvement)
With both patches: 1 minute 50 seconds (70% reduction)

The online mode loading time finally approached story mode performance.

The Impact

t0st reported the findings to Rockstar through their bug bounty program. Despite the program typically focusing on security vulnerabilities, Rockstar recognized the significance of the discovery.

Result:

Rockstar confirmed the issue and released an official patch in March 2021
t0st received a $10,000 bug bounty reward
The fix dramatically improved the experience for millions of players
t0st published the full technical breakdown and proof-of-concept code on GitHub

This discovery stands as a reminder that even AAA games from major studios can ship with fundamental performance bugs that persist for years—and that dedicated community members can make a real difference.