Reactor multiplayer engine for Unity Free to develop locally. Free to self-host up to 32 CCU. Cloud hosting from $20/mo. See pricing →
Build the multiplayer game
your engine said you couldn't.
You shouldn't have to shrink your game design to fit your netcode. Reactor makes sure you don't: it compresses your traffic automatically, with no serialization code to write.
Efficient out of the box.
Reactor compresses your traffic automatically, with no serialization code to write and no tuning passes. In a controlled benchmark that meant 17x less transform data than Unity's Netcode for GameObjects and 9.5x less than Photon Fusion 2, with wire bandwidth about 6x lower at typical loads.
See the bandwidth comparison →Click to deploy. Nothing to babysit.
Push a server to Reactor Cloud and it runs. Matchmaking, scaling, and persistent data come from the same managed backend, so you operate a game, not infrastructure. Every layer ships in the box and every layer is swappable: run cloud-hosted or self-hosted, bring your own physics or use ours.
KS Reactor Unity SDK
Component-based sync for transforms, animations, physics, and custom properties. Works with any Unity controller, any lifecycle.
KS Reactor Server
C# server runtime with server-authoritative physics, custom room scripts, tick-rate control, and cluster-level persistence.
KS Reactor Cloud
Managed hosting with zero-config matchmaking, region selection, and automatic scaling. From $20/mo.
Replaces: Photon Cloud, Normcore
Multi-threaded physics
Server runs Unity physics on parallel threads with deterministic tick timing. Scale to hundreds of concurrent simulations.
Cluster and room messaging
Cross-room RPCs and persistent state across the cluster. Build sharded MMOs without a custom messaging layer.
Self-hostable, no lock-in
Run the server runtime on your own infrastructure. Docker images, Linux binaries, Kubernetes-ready.
Replaces: Unity Relay, Photon SaaS lock-in
Built to scale
Low bandwidth alone won't carry you beyond 1,000 CCU. Reactor backs the compression with the engine systems that make large object counts and high concurrency work in production.
Sync groups and interest management
Spatially partition entities so each player only receives updates for what's relevant to them. Your world can grow without your bandwidth growing with it.
Server-authoritative physics
Raycasts, sweeps, and overlap queries all run as real physics on the server. The client is never trusted to report its own hits.
Built-in prediction and interpolation
Customizable predictors smooth motion and properties between server snapshots. Reconciliation against the server ships with the engine, so it isn't something you build yourself.
Turn single-player into multiplayer
Drop component-based transform, animation, and ownership sync onto a single-player controller you already have. There's no rewrite, and no separate client and server codepaths to keep in sync.
The new benchmark for snapshot replication
Snapshot-based replication is usually pitched for shooters, but it fits persistent worlds, physics sandboxes, and strategy games just as well.
High-CCU shooters and battle royales
Server-authoritative input, hit-scan and projectile, multi-threaded controllers. Tested past 1,000 CCU.
Persistent worlds and MMOs
Rooms run for months at a time. Cluster persistence and cross-room messaging for sharded worlds.
Crowds, sims, and physics-driven games
Sync hundreds of dynamic entities at 2 bytes per update. Every interaction is driven by the physics simulation rather than canned animation.
RTS, sandboxes, and strategy
Dense object counts that would saturate other netcodes. 120Hz tick rates available where you need them.
Trusted by studios using Reactor in production
Also from KinematicSoup
Scene Fusion: real-time Unity co-editing
Multiple developers editing the same scene at the same time, live. Scene Fusion syncs transforms, prefab edits, and terrain changes across the team as you work.
Recognition
Start building. No credit card required.
Free to develop locally. Free to self-host up to 32 CCU. Upgrade when your player count does.