Files within the archive are often compressed using LZ4 or Zlib (depending on the specific resource type and platform). The RAGE engine streams compressed data into RAM and decompresses it on the fly using the console/PC's SPU or CPU.
The filename X64u.rpf follows the Rockstar naming standard introduced in the HD Universe titles (GTA IV, Max Payne 3, GTA V). X64u.rpf
ps3.rpf or xbox360.rpf. The X64 prefix denotes content compiled for 64-bit PC and modern console architectures.X64a.rpf, X64b.rpf, etc. The specific letter u typically signifies a grouping of specific asset types (often related to props, vegetation, or specific LODs depending on the game version).X64u.rpf is a proprietary archive container utilized by Grand Theft Auto V on x64 (64-bit) architectures. It functions as a massive asset repository, storing critical game data including 3D models, textures, collision data, and shader libraries. Unlike standard Loose files, .rpf archives function similarly to .zip or .pak files but are optimized for the RAGE engine's streaming system, allowing for rapid seek-and-read operations required by an open-world streaming engine. Understanding X64u
Since recent GTA V patches (2020 onwards), Rockstar has shifted much of the data that used to live in X64u.rpf into the update\update.rpf file. This allows Rockstar to patch the game without re-delivering the massive 2GB X64u.rpf file. However, the original X64u.rpf remains a fallback for legacy assets. X64: Indicates the architecture