Unreal Engine 5.9 MegaJam Preview Arrives

Epic Games has released an early preview of Unreal Engine 5.9 which has larged been developed by AI agents (reviewed and tested by real people) with a focus on browser based gaming.

The preview isn't your typical update to Unreal Engine. Epic has used it to experiment with a different approach to their own software development as AI agents wrote much of the code unreal the direction of a small team of engineers.

It was put together in around one week ahead of the Epic AI MegaJam which takes place between Novmeber 12 and 15 2026.

It comes ahead of the expected release of Unreal Engine 5.9 which is expected next year.

Building with AI

According to Epic a handful of developers directed multiple AI agents working in parallel to bring tools from its Unreal Engine 6 development branch in to Unreal Engine 5.9.

These agents were responsible for writing the code needed to bring browser support back to Unreal Engine using the discontinued HTML5 platform from Unreal Engine 4 as a starting point.

Real humans were responsible for directing, reviewing and testing the work.

This test represents a huge change in how major game engines can be developed. Rather than developers writing every part of the code themselves, Epic is seeing what happens in workflows where engineers coordinate AI agents to complete development tasks.

Unreal Engine back in the browser

The biggest thing here is the return of Unreal Engine in the browser. Unreal Engine 4 offered HTML5 exports, but support was discontinued with Unreal Engine 5 focused on native platforms.

This Unreal Engine 5.9 preview sees Epic expermenting with bringing games directly to modern browsers using WebAssembly and WebGPU.

The limitations with this preview mean developers need a C++ project with a version of the Unreal Engine built from source and Chrome offers the best gaming expereince. Longer build times and performances issues and incomplete functionality are also things to be aware of.

AI in Unreal Editor

The 5.9 preview is also introducing tools for AI assistance within Unreal Engine.

A new Unreal Assistant panel will allow developers to work with agents such as Claude Code, Codex, Cursor and OpenCode directly within the editor.