Our experience building an MMO tech demo with Unreal Engine 5.6
Hi everyone 
,
I am working for CipSoft, a game development studio from Germany with many years of experience building and operating online games. My task for the past few months was to evaluate several engines and networking approaches for MMO development, including Unreal Engine 5.6.
As part of this evaluation, we built a small but functional 3D MMO tech demo in Unreal and created a short trailer that is linked below. We wanted to share our experience, especially from a networking and MMO perspective, in case it is useful to others.
Here’s the short video of our evaluation:
[YouTube]
What we built 
We created a simple third-person multiplayer tech demo.
- 3D world
- Third-person character controller
- Combat with projectiles
- AI enemies
- Respawning players and enemies
Client and server were developed in the same project and compiled using separate build targets.
For load testing, we launched multiple bot clients using the -nullRHI parameter to simulate gameplay without rendering.
What we liked 
Unreal is an extremely powerful 3D engine. The rendering quality and built-in systems for landscapes, materials, animation and effects are very mature. Technologies like Lumen and Nanite make it clear that Unreal is built for large scale 3D productions.
The editor is feature-rich and comes with many integrated tools out of the box, including terrain editing, material graph editing and profiling tools such as Unreal Insights. For large 3D worlds, the toolchain feels complete and production-ready.
In terms of networking, Unreal provides multiple replication systems, including the default replication system, Replication Graph and Iris. For our tech demo we used Iris. The built-in replication model significantly reduces the amount of custom networking code required compared to more low-level approaches.
The server was running on a Linux virtual machine with 2 CPU cores and 2 GB of RAM. The bot clients were distributed across six separate Windows machines.
With this setup, we were able to reach around 450 concurrent connections during stress tests. Stable and reasonably smooth operation was possible up to roughly 250 concurrent connections. These numbers were higher than we originally expected, based on various statements and discussions we had seen online regarding Unreal’s MMO scalability.
It is important to note that we did not heavily focus on network optimization during this evaluation. The tech demo was intentionally kept simple and close to default engine behavior in order to assess baseline performance. We did not implement advanced replication filtering, bandwidth optimization, custom prioritization strategies or deeper architectural scaling approaches. With additional dedicated networking optimization, higher scalability may well be achievable.
What we found challenging 
Unreal is a heavyweight engine. The editor is powerful but resource intensive and requires strong hardware. Even small projects take up significant disk space, and initial build times can be long. Building the engine from source, which is required for certain server configurations, takes considerable time and setup effort.
The learning curve is noticeably steeper compared to Unity or Godot. The engine exposes a large amount of functionality, which is powerful but can feel overwhelming at first.
From a networking perspective, while Iris performed well in our tests, we had to adjust engine-level settings to allow more than 128 network connections. This required modifying Unreal Engine source code.
Another limitation we observed is that the dedicated server currently runs single-threaded on the CPU in our setup, which limits scalability unless additional architectural measures are taken. Under higher loads, we observed increasing latency once server resources were saturated.
Overall Conclusion 
Overall, Unreal Engine 5.6 proved to be a very strong candidate for MMO development, particularly for large-scale 3D worlds. The rendering quality, built-in toolchain and replication systems provide a solid foundation for online games.
From a pure scalability standpoint, Unreal handled higher concurrent player counts in our tech demo than some other engines we evaluated. However, this comes at the cost of higher hardware requirements, longer build times and increased complexity.
For studios with strong C++ expertise and the necessary infrastructure, Unreal offers a powerful and production-proven ecosystem. For smaller teams or rapid iteration-focused workflows, the heaviness of the engine can slow things down.
We share this not as criticism, but as a transparent report from our evaluation process. If there are architectural approaches or scaling strategies we should have explored further, we would genuinely appreciate the discussion.