Some components of Slipspace were almost 25 years old. Halo Studios decided that was enough.
Halo: Campaign Evolved arrived on 28 July, and most of the coverage went where you would expect. It is the first mainline Halo to appear on a PlayStation console, which is still a strange sentence to type after twenty-five years of Halo being the reason you bought an Xbox.
The more consequential thing about the game has nothing to do with which box it runs on. It is that Halo was not built in Halo’s engine.
Console game development has been quietly reorganising itself around this decision for several years, and Halo is the largest example so far. Slipspace, the engine that ran Halo Infinite and carried DNA going back to Bungie’s original toolset, is not what Campaign Evolved was made in. Halo Studios moved to Unreal Engine 5, said so publicly, explained why in unusual detail, and has now shipped the first game to prove the pipeline works.
The reasoning they gave is worth reading properly, because it is not the reasoning most people assume.
Why Halo moved off its own engine
The public explanation came in October 2024, when 343 Industries became Halo Studios and announced the move alongside something called Project Foundry.
Chris Matthews, the studio’s Art Director, put the technical case bluntly: “Respectfully, some components of Slipspace are almost 25 years old…there are aspects of Unreal that Epic has been developing for some time, which are unavailable to us in Slipspace.”
That is the part people quote. The part that matters more is what maintaining those components cost. Before the switch, a substantial share of the studio’s staff was dedicated to developing and maintaining Slipspace rather than making games. A studio that is also a software company is competing with itself for its own engineers, and every hour spent upgrading a renderer is an hour not spent on a level.
Elizabeth van Wyck, the studio’s COO, framed it as a production problem rather than a technology one: “The way we made Halo games before doesn’t necessarily work as well for the way we want to make games for the future.”
Project Foundry was how they tested that. It was not a tech demo. Matthews described it as built with “the same rigor, process, and fidelity as a shipped game would be” – three real-time environments made in Unreal, specifically to find out what moving the studio’s pipelines would actually require. Van Wyck was candid that it was not in the plan: “When we decided to do Foundry, it wasn’t, at that point, in our plan…we needed to pause and educate and understand what our capability is.”
Studio head Pierre Hintze tied it to release cadence: “We believe that the consumption habits of gamers have changed – the expectations of how fast their content is available.”
Read together, that is a studio saying it could no longer afford to build the tools and the games at the same time.
Halo is not an outlier
If this were only Halo, it would be a Halo story. It is not.
CD Projekt Red retired REDengine, the technology behind The Witcher 3 and Cyberpunk 2077, and moved the next Witcher games to Unreal Engine 5. Hangar 13 and 2K dropped the proprietary Fusion Engine for Mafia: The Old Country. Eidos-Montréal abandoned its Dawn Engine, explicitly to cut internal technology maintenance and put the time into production instead.
The pattern is consistent, and the logic is the same every time. A custom engine is a permanent tax paid in engineering salaries, and it gets more expensive as hardware targets multiply. Xbox studios now ship to Series X, Series S, PC and increasingly PlayStation, which means every renderer change has to be validated four ways.
It is worth saying that the trend is not universal. OnceLost Games went the other direction for Wayward Realms, leaving Unreal Engine 5 for a custom engine, and studios with deep, specific technical needs still build their own tools for good reasons. A shared engine is a trade rather than a free win, and a team that needs precise control over its renderer sometimes gets there faster by owning one.
But for a studio whose problem is throughput rather than novelty, the maths keeps pointing the same way.
What an engine change actually does to a team
Here is the part that gets skipped. When a studio changes engine, its most experienced people become less experienced overnight.
A senior technical artist with a decade in a proprietary toolset holds knowledge that is genuinely valuable and suddenly not transferable. Nothing about their judgement got worse, but their muscle memory is now in the wrong software. Multiply that across an art department and you have a studio that is simultaneously learning a new engine and shipping a game in it.
Van Wyck named the flip side of this as one of the reasons for the move: adopting Unreal shortens onboarding for developers who already know industry-standard tools. That is the whole argument in one line. Unreal is not chosen because it is technically superior to every in-house engine. It is chosen because the industry already knows it, so people can be added to a production without a six-month runway.
Which is why external teams have become structural rather than occasional. A studio mid-migration does not need generalists, it needs people whose default toolset is already the one being adopted. Studios working in console game development on that basis have shipped Unreal titles across Xbox for years, which is the entire point of bringing them in.
Devoted Studios did end-to-end lighting on Halo: Campaign Evolved. It has also contributed to Unreal releases including Arc Raiders for Embark, Obsidian’s Avowed, The Outer Worlds 2 and Grounded 2, Steel Wool’s FNAF: Secret of the Mimic, and Skybound’s Invincible VS – different disciplines each time, on a platform where a game has to hold together on Series S as well as Series X.
What it means for the games
Practically, two things.
Xbox releases should get more frequent, because that was the stated goal. A studio not paying an engine tax has more engineers on content, and a studio using Unreal can add people who are useful in week one instead of month six.
The second is about identity. Games built in a shared engine can start to resemble each other, because the defaults are the same and the defaults are good enough to ship. Halo Studios clearly saw that coming, which is exactly why Project Foundry existed: the point was to make Unreal look like Halo before a line of the game was written, rather than finding the problem halfway through production.
Twenty-five years in, Halo has changed engines, and Campaign Evolved is the first game to come out the other side of that decision. Judging by how many studios are making the same call, it will not be the last.
