Continuous integration and continuous deployment changed software development. Build on every commit. Run tests on every pull request. Deploy to production in minutes. The model is so standard in web and mobile development that new engineers often assume it works the same way for games.
It does not. Not automatically. The same principles apply — automated builds, test coverage, reproducible environments — but the implementation is different enough that teams trying to port their web CI setup directly to a game project end up with something slow, brittle, and expensive.
Why Game CI Is Different
Build times are long
A web application build might take 2-5 minutes. A full Unreal Engine build with shaders compiled for multiple platforms can take 45 minutes to two hours. Running that on every commit is not feasible. You need a tiered approach: lightweight validation on every commit, full builds on a schedule or on merge to certain branches.
Asset import is part of the build
Importing assets into Unity or Unreal is not an optional step — it is part of the build process. Importing a complex 3D scene for the first time can take minutes. Reimporting all assets from scratch every build run is unacceptably slow. You need a caching strategy for imported assets, which means your build machines need persistent storage and you need cache invalidation logic when source assets change.
Platform-specific builds multiply complexity
A game ships to multiple platforms — PC, console, mobile, maybe VR. Each platform target requires a different build configuration, different SDKs, different signing credentials. Your CI system needs to manage platform-specific build agents with the right tools installed, which means you cannot use generic cloud CI runners for most platform targets. Console builds require hardware devkits or licensed emulation environments that cannot run on standard cloud infrastructure at all.
Tests are harder to write
Unit testing for game logic is possible and worthwhile. But testing gameplay behavior — "does this level feel right," "does the animation blend correctly," "does the physics simulation produce the right outcome" — is either manual or requires specialized tooling. Most game studios have much lower automated test coverage than equivalent software teams, which means CI cannot be a quality gate in the same way.
What Actually Works
Nightly full builds
Run a complete build of the game — all platforms, all configurations — once per night on the previous day's main branch. This gives you a daily playable build that QA can test, and a clear signal when something broke the build. Nightly builds catch integration issues before they compound.
Per-commit code compilation checks
On every commit to the main or milestone branch, run a compilation check for the code changes only. Do not import all assets, do not package the game. Just compile the C++ or C# changes and run any unit tests. This catches syntax errors and obvious regressions quickly without the overhead of a full build.
Incremental build caching
Set up build machines with persistent asset import caches. The first build after a cold start is slow. Subsequent builds that only changed a few assets should be fast. This requires your build system to track which assets changed between commits and reimport only those. Both Unity and Unreal have mechanisms for incremental builds — they need careful configuration to work reliably in a CI context.
Change-triggered platform builds
Not every change needs to build for every platform. A code change that only affects PC gameplay does not need to trigger a console build. Set up build triggers that inspect what changed and only run the platform builds that the change could affect.
Common Mistakes
Running full builds on every commit is the most common mistake. Teams set this up because it seems thorough, then the build queue backs up, engineers stop waiting for results, the feedback loop breaks, and the CI system becomes something everyone ignores.
Using generic cloud CI runners for game builds is the second most common mistake. Most cloud CI providers offer Linux or Windows containers with standard software stacks. Game engines are not standard. Setting up Unreal Engine or Unity on a cloud runner from scratch takes 20-30 minutes on a good day. The licensing requirements for certain platform SDKs prohibit cloud deployment entirely.
Ignoring asset pipeline in the CI design is the third. Studios set up code CI, it works, they call the project done. Six months later, the build fails on a QA machine because someone committed a corrupt texture three weeks ago and nobody noticed until now. Asset validation — checking that assets import without errors — belongs in the build pipeline as much as code compilation does.
The Version Control Connection
CI and version control are tightly coupled. A CI system that cannot efficiently get a clean workspace — checking out code and downloading only the relevant assets — will be slow regardless of how fast the build hardware is. This is one reason the LFS bandwidth problem compounds at scale: every CI run that downloads all assets is multiplying the network cost.
Diversion's lazy asset fetching is designed to help here. Build machines can check out a branch and fetch only the assets that changed relative to the previous build, rather than downloading the full repo state. For a studio running builds multiple times per day, that difference in download time compounds into real hours per week.
Game CI is a real engineering problem with no off-the-shelf solution that works for every studio. The studios that get it right treat it as infrastructure work, invest in it early, and maintain it like any other production system. The ones that do not spend a lot of time asking why their builds are broken.