Diesel 3.0: Modernizing a 13-Year-Old Engine for Payday 2

Retaining the Player Base: The Business of Legacy Support

In modern game development, the industry consensus is to migrate players to a sequel. However, when a sequel struggles to capture the community, developers face a critical choice: double down on the new product, or modernize the classic that players refuse to abandon.

Sidetrack Games, the studio that took over development of Payday 2 in 2025 while Starbreeze Studios focused on Payday 3, recently made a bold choice in this arena. They announced a massive engine upgrade for the 13-year-old cooperative heist game, dubbed Diesel 3.0.

This is a complete architectural overhaul of a proprietary engine that debuted in 2001. For game developers, this is a fascinating case study in legacy codebase modernization, showing how to safely swap the foundation of a live-service game without collapsing the ecosystem.

The 32-Bit Ceiling: Resolving the Out-of-Memory Bottleneck

The primary driver behind the Diesel 3.0 upgrade is the transition from a 32-bit architecture to a 64-bit architecture.

In a 32-bit execution environment, a process is hard-capped at 4GB of addressable virtual memory. When Payday 2 launched in 2013, 4GB was plenty. However, after 13 years of continuous content updates, dozens of heists, hundreds of weapons, and a massive array of character skins, the game's asset registry has grown exponentially.

This resulted in chronic 'out-of-memory' (OOM) crashes, particularly during long play sessions or on content-heavy maps. When the engine tried to load assets that pushed the memory footprint past the 4GB boundary, the game crashed.

By migrating to a 64-bit architecture, Sidetrack Games has raised the virtual memory limit to 16 exabytes, effectively removing RAM capacity as a bottleneck. The engine can now keep more assets resident in system memory, leading to:

• A significant reduction in runtime crashes.
• Improved asset loading speeds, as the engine doesn't have to constantly swap textures out of RAM.
• Greater stability on systems running high-resolution textures or user-created mods.

DirectX 11 Transition: Performance Over Visuals

Alongside the 64-bit shift, Diesel 3.0 replaces the ancient DirectX 9 rendering pipeline with DirectX 11.

Historically, moving to a newer rendering API is done to unlock modern graphics features like ray tracing. But for Sidetrack Games, the transition is strictly a performance play. The goal is not to make Payday 2 look like a 2026 title, but to optimize how it communicates with modern GPUs.

DirectX 9 has significant driver overhead. Each draw call issued by the engine requires substantial CPU translation. On modern multicore CPUs, DirectX 9 struggles because it is heavily single-threaded; the render thread acts as a bottleneck for the entire engine.

DirectX 11 introduces better multithreading support and driver-level optimizations. This modernization results in several key benefits:

1. Lower CPU Bottlenecks: The engine can feed draw calls to the GPU much faster, resulting in higher and more stable frame rates, especially during chaotic assaults with dozens of AI enemies on screen.

2. Reduced VRAM Usage: Better memory management protocols in DirectX 11 allow the engine to keep its video memory footprint low, preventing stuttering on cards with limited VRAM.

3. Improved Compatibility: Modern graphics card drivers are increasingly deprecating native DirectX 9 support, delegating it to translation layers (like Microsoft's D3D9On12). Native DirectX 11 support guarantees direct hardware access and prevents driver-level emulation bugs.

The Packaging Overhaul: Shrinking the Footprint by 62%

One of the most impressive achievements of the Diesel 3.0 upgrade is the dramatic reduction in disk space. Sidetrack Games has rewritten the engine’s asset packaging and bundling systems, shrinking the game's install footprint from approximately 86GB down to just 32GB.

Over 13 years, Payday 2 accumulated massive packaging debt. The original asset bundle structure was designed for mechanical hard drives (HDDs), where files were frequently duplicated to place them closer together on the physical disk platter, minimizing head seek times. On modern solid-state drives (SSDs), seek times are virtually zero, making asset duplication obsolete and wasteful.

Sidetrack Games achieved this 62% size reduction through:

• Deduplication: Removing thousands of duplicate models, textures, and audio files that were duplicated across different heist packages.
• Modern Compression: Switching to high-efficiency compression algorithms that compress assets tighter without adding significant CPU decompression overhead during load screens.
• Streamlined Packaging: Re-architecting how files are bundled, which also reduces the time required for Steam to apply game patches.

The Modding Conundrum: Breaking to Rebuild

No discussion of Payday 2 is complete without its modding community. The game has one of the most active modding scenes in PC gaming, with players modifying everything from the UI to entirely new gameplay mechanics and custom maps.

Because Diesel 3.0 changes the fundamental architecture (32-bit to 64-bit) and the asset packaging system, it will inevitably break almost every existing mod. Mod loaders that hook into the game's executable memory space will fail due to the change in memory address structures, and custom assets will not load due to the new bundling formats.

Sidetrack Games is handling this situation by scheduling an open beta on Steam that runs from June 30, 2026 through the end of July. This gives the modding community a full month to test their tools, rewrite their memory hooks, and update their asset packers. Sidetrack has committed to providing documentation on the new file formats and actively collaborating with mod creators during the beta to ensure a smooth transition.

It is a reminder that in game production, technical modernization always carries a human cost. Breaking user-generated content can alienate a game's most passionate advocates, but by providing a dedicated sandbox beta and direct engineering support, Sidetrack is showing how to manage this friction responsibly.

Lessons in Legacy Codebase Modernization

The Diesel 3.0 upgrade is a testament to the enduring value of solid design and targeted refactoring. Upgrading a 13-year-old engine is an expensive, high-risk endeavor, but it is often more cost-effective than attempting to salvage a sequel that has failed to find its footing.

For developers working on long-term projects, the Payday 2 modernization provides three clear lessons:

1. Solve memory constraints first: 64-bit migration is the ultimate stability upgrade for long-lived codebases.

2. Optimize APIs for overhead, not visuals: Moving to modern rendering APIs is just as valuable for CPU driver overhead reduction as it is for graphical upgrades.

3. Clean up packaging debt: Do not let asset structures designed for obsolete hardware (like HDDs) bloat your modern builds.

As the open beta launches on June 30, developers and players alike will be watching to see if this massive architectural gamble pays off.