Unity Multiplayer Engines Compared: Reactor, Photon Fusion, NGO, Mirror, and Coherence

There is no single best Unity multiplayer engine. The right choice depends on what you are building, how much infrastructure you want to manage, and what your bandwidth and scale requirements look like. This is a practical breakdown of the main options.

Quick reference

Photon Fusion 2

Photon Fusion 2 is the most widely used Unity multiplayer solution. The ecosystem is large: there are tutorials, community answers, and third-party integrations for almost anything you might need. If you get stuck, someone has probably solved the same problem and written about it.

Fusion has good client-side prediction and rollback, which makes it a solid choice for competitive games where latency compensation matters. Photon manages the relay infrastructure, so you do not need to run your own servers.

The downsides are cost and bandwidth. Photon prices on CCUs, which means you pay based on peak concurrent users rather than actual usage. Bandwidth is not a focus. In a controlled benchmark against Reactor using identical scenes, Fusion used about 9.5 times more bandwidth per player. That gap matters at scale, but for most games at moderate player counts it is manageable.

Use Photon Fusion 2 if: you want the largest community and ecosystem, your game is a competitive or action game, and you are comfortable with CCU pricing.

Unity Netcode for GameObjects (NGO)

NGO is Unity’s official multiplayer solution. It is free, open source, and deeply integrated with the Unity editor. The documentation is good and it follows Unity conventions closely, so the learning curve is lower if your team already knows Unity well.

NGO works best when you need Unity functionality running directly on the server. If your game logic is tightly coupled to Unity components and you want a headless Unity server instance handling game state, NGO is a natural fit. Individual server instances with Unity running the full simulation are where NGO is at its strongest.

The trade-off is infrastructure. NGO does not include managed hosting. You run your own servers, which means provisioning, monitoring, and scaling are your responsibility. For teams with backend experience this is fine. For teams without it, the operational overhead adds up.

Use NGO if: you need a lot of Unity-native server-side functionality, your architecture calls for individual Unity server instances, and you have backend engineering capacity on your team.

Mirror

Mirror is free, open source, and has been around long enough to have a large community and a lot of answers on forums and Discord. The API is familiar to anyone who worked with Unity’s old UNET system.

It is a good choice for indie developers or small teams on a tight budget. You run your own servers, so infrastructure is your problem, but the cost floor is low. Community support is solid.

Mirror is not built for extreme scale or physics-heavy simulations. It works well for games with moderate player counts and straightforward synchronization requirements.

Use Mirror if: you are an indie developer, self-hosting is fine, and budget is a priority.

Coherence

Coherence is one of the newer entrants and has gained traction on the strength of its developer workflow. Developers who have used it tend to find the experience well-designed and approachable.

Under the hood, Coherence handles network data packing the same way most solutions do. It does not have a particular bandwidth or physics advantage. It is a competent solution for standard game types where the development experience matters more than raw performance.

Use Coherence if: you are building a standard multiplayer game and want a modern, well-designed workflow.

Reactor

Reactor is built around server authority, physics simulation, and bandwidth efficiency. The compression is automatic and significant. In a controlled benchmark against Photon Fusion 2 and NGO using identical scenes, Reactor used 2 billion bits where the others used 19 and 34 billion respectively. The benchmark is public if you want to run it yourself.

That benchmark represents a specific controlled case. Real games tend to do better. Reactor builds data models from your actual game state and optimizes them automatically, so the compression improves as it learns the patterns in your data.

In Kazap.io, a 2D browser multiplayer game, Reactor compressed transforms down to about half a byte each. Braains2, a 3D top-down physics game with 100 players and 150 physics objects, came in at under a byte per transform. Ruins, a 3D physics destruction FPS demo we built to test the engine, frequently runs below a byte per transform despite the complexity of the simulation. The benchmark is a floor, not a ceiling.

The managed hosting question is handled by Reactor Cloud. One-click deployment, no servers to provision, no infrastructure to monitor. The free tier covers development and up to 32 concurrent users. Paid plans scale from there without requiring any DevOps work.

Reactor is the right choice when bandwidth and physics are the constraint. Large crowds, dense physics simulations, open worlds with thousands of entities, games where bandwidth costs are a real concern. The Braains2 case study shows what this looks like in practice: 100 players at 30Hz with 150 physics objects, at 35 kbps per server.

The server runtime is designed to be lightweight. It contains only what is needed to run scripts, simulation, and networking: no editor overhead, no rendering subsystems, nothing that does not affect game state. It is highly concurrent and scales across multicore server processors. Memory overhead is in the tens of megabytes, which means you can run more server instances on the same hardware compared to solutions that require a full Unity headless build.

Reactor has two control system models depending on the game type.

The server-authoritative controller takes client inputs and replicates them to both the server and the client-side prediction system simultaneously. The developer provides the motion code (assigning velocities, sweeping movement) and that same code runs in both contexts. On the client, a predictor uses it to generate instant feedback. On the server, it drives the simulation directly. The two states are then converged by the predictor. Reactor ships with several predictors out of the box and supports custom implementations. This is the right model for physics-based games with a low tolerance for desyncs, where authoritative physics and responsive controls both matter.

The shared mode lets the server assign ownership of entities to any connected Unity instance, whether that is a game client or a headless authoritative build. Developers can write a standard single-player controller and Reactor handles replicating the key state to all other connected clients automatically. This model works well for simpler games with minimal physics, and for MMOs where offloading logic like pathfinding or animation to separate processes helps the server scale. It is also the easier path for converting an existing single-player game to multiplayer.

The runtime compiles separately from Unity. A change to client code does not trigger a server recompile and a change to server code does not trigger a Unity recompile. On larger projects this keeps iteration times short in both directions.

The trade-offs: the community is smaller than Photon’s, public documentation is less extensive, and Reactor’s workflow is Unity-oriented. The engine itself can be adapted to other C# game clients (we have used MonoGame on the client side), but the tooling and integration layer are built around Unity. If ecosystem size and community support are your top priorities, Photon Fusion is a better fit.

Use Reactor if: you want server authority and managed hosting without DevOps work. Or if your game involves physics simulation, large crowds, or high entity counts where bandwidth efficiency matters. The server runtime compiles separately from Unity, so a change on the client side does not trigger a server recompile and vice versa. Iteration stays fast as the project grows.

How to choose

If you are not sure where to start, a few questions narrow it down quickly.

Do you need physics simulation, large crowds, or high entity counts? Reactor is the clearest choice here. The bandwidth advantage compounds as your simulation grows.

Do you need Unity-native logic running directly on the server? NGO is worth a serious look, particularly if you want individual Unity server instances and have backend engineering capacity.

Is budget the primary constraint? Mirror is free and has a large community. NGO is also free if you are comfortable managing infrastructure.

Do you want managed hosting with no infrastructure work? Reactor Cloud or Photon both handle this. Reactor is stronger on bandwidth and physics; Photon is stronger on ecosystem and community.

Are you building a competitive game where prediction and rollback matter most? Photon Fusion 2 has the most mature implementation of this and the largest community around it.

If you want to try Reactor, it is free to get started. Development is free, and self-hosting is free up to 32 CCU.