# Photon Engine Documentation

> Photon Engine is a suite of networking SDKs and managed cloud services (Photon Cloud) for building real-time multiplayer games and applications in Unity, Unreal Engine, and Godot. The main products are Fusion (state-synchronization netcode — Fusion 2 for Unity, with Fusion 3 bindings for Unreal Engine and Godot), Quantum (deterministic ECS engine with prediction/rollback), Realtime (low-level client SDKs), Voice (voice chat), Chat, and the self-hosted Photon Server. Conceptual and how-to docs live on doc.photonengine.com; generated class/method API references live separately on doc-api.photonengine.com.

Notes for agents:

- URLs containing `/current/` always point to the *latest* version of a product's docs. Every page is also reachable under an explicit version segment (e.g. `/fusion/v2/` instead of `/fusion/current/`). If you know which SDK version the project uses, substitute that version into the URL to get version-accurate documentation; only use `/current/` when the latest version is genuinely what you want. `/current/` links may change content when a new major version is released.
- What `/current/` resolves to today (use this to substitute exact versions): Fusion for Unity → `v2`; Fusion for Unreal and Fusion for Godot → `v3`; Quantum → `v3`; Voice → `v2`; PUN → `v2`; Photon Server → `v5`. Realtime, Chat, Tournament SDK, and AR/VR each have a single active line, so `/current/` is simply the latest. Fusion for Godot is additionally split by topology into two trees: `v3-shared-authority` and `v3-client-server`.
- "Fusion" spans two major versions depending on the engine. The current Unity SDK is **Fusion 2** (`/fusion/`). **Fusion 3** is the next-generation line and currently ships as **Fusion for Unreal** (`/fusion-unreal/`) and **Fusion for Godot** (`/fusion-godot/`). For Unity, use Fusion 2 — do not route Unity users to the Unreal or Godot pages.
- A raw Markdown version of any page is available by appending `.md` to its URL (e.g. https://doc.photonengine.com/fusion/v2/fusion-intro.md) - prefer it over the HTML when ingesting content.
- Docs are available in English (default), Japanese (`/ja-jp/`), Korean (`/ko-kr/`), and Traditional Chinese (`/zh-tw/`) by prefixing the path with the locale.
- The `.md` suffix, version-segment, and locale conventions above apply to **doc.photonengine.com only**. The generated class/method API reference is a separate site (doc-api.photonengine.com) that does *not* support the `.md` suffix — see the "API Reference" section below.
- Older product versions (Fusion 1, Quantum 1/2, PUN 1, Server 4, Bolt) remain online under their version segment but are not recommended for new projects.
- A full machine-readable URL inventory is available at https://doc.photonengine.com/sitemap.xml

## Fusion 2 (Unity netcode)

- [Fusion 2 Introduction](https://doc.photonengine.com/fusion/current/fusion-2-intro): Overview of Fusion, a high-performance state-synchronization networking library for Unity.
- [Choose a Topology](https://doc.photonengine.com/fusion/current/fusion-choose): How to pick between Fusion's network topologies — Shared Authority, Client Host, and Dedicated Server (plus single-player).
- [SDK Download](https://doc.photonengine.com/fusion/current/getting-started/sdk-download): Download and install the Fusion 2 SDK.
- [Create a Fusion AppId](https://doc.photonengine.com/fusion/current/getting-started/appid-instructions): Create a Photon Cloud application and get the App ID Fusion needs to connect.
- [Host Mode Basics Tutorial](https://doc.photonengine.com/fusion/current/tutorials/host-mode-basics/overview): Step-by-step first-game tutorial for Host/Server Mode (scenes, prediction, physics, RPCs).
- [Shared Mode Basics Tutorial](https://doc.photonengine.com/fusion/current/tutorials/shared-mode-basics/overview): Step-by-step first-game tutorial for Shared Mode (player movement, network properties, RPCs).
- [Coming from PUN 2](https://doc.photonengine.com/fusion/current/getting-started/migration/coming-from-pun2): Migration guide for PUN 2 developers.
- [Coming from Fusion 1](https://doc.photonengine.com/fusion/current/getting-started/migration/coming-from-fusion-v1): Migration guide from Fusion 1 to Fusion 2.

## Quantum (deterministic engine)

- [Quantum Introduction](https://doc.photonengine.com/quantum/current/quantum-intro): Overview of Quantum 3, a deterministic ECS game engine with prediction/rollback netcode.
- [Initial Setup](https://doc.photonengine.com/quantum/current/getting-started/initial-setup): Project setup and first steps with the Quantum 3 SDK.
- [FAQ](https://doc.photonengine.com/quantum/current/getting-started/faq): Frequently asked questions about Quantum.
- [Asteroids Tutorial](https://doc.photonengine.com/quantum/current/tutorials/asteroids/1-overview): Complete beginner tutorial building a multiplayer Asteroids game (setup through collision detection).
- [Quantum Starter Sample](https://doc.photonengine.com/quantum/current/game-samples/quantum-starter/overview): Starter sample project for Quantum 3.
- [Migration Guide](https://doc.photonengine.com/quantum/current/getting-started/migration-guide): Migrating from Quantum 2 to Quantum 3.

## Fusion 3 — Unreal / Godot

The next-generation Fusion line for Unreal Engine and Godot. (For Unity, use Fusion 2 above.)

- [Fusion for Unreal Introduction](https://doc.photonengine.com/fusion-unreal/current/fusion-intro): Fusion 3 networking for Unreal Engine.
- [Fusion for Unreal Quick Start](https://doc.photonengine.com/fusion-unreal/current/getting-started/quick-start-guide): First steps with Fusion in Unreal Engine.
- [Fusion for Godot — Shared Authority](https://doc.photonengine.com/fusion-godot/v3-shared-authority/fusion-intro): Fusion 3 for Godot, shared-authority topology (the variant the site navigation defaults to).
- [Fusion for Godot — Client/Server](https://doc.photonengine.com/fusion-godot/v3-client-server/fusion-intro): Fusion 3 for Godot, client-server topology.

## Realtime

- [Realtime Introduction](https://doc.photonengine.com/realtime/current/getting-started/realtime-intro): Overview of the Photon Realtime low-level client SDKs (C#, C++, and more).
- [Quick Start](https://doc.photonengine.com/realtime/current/getting-started/quick-start): Connect, join rooms, and exchange events with Photon Realtime.
- [Unreal Engine Setup](https://doc.photonengine.com/realtime/current/getting-started/unreal-engine): Using the Realtime C++ SDK with Unreal Engine.
- [Obtain Your App ID](https://doc.photonengine.com/realtime/current/getting-started/obtain-your-app-id): Creating a Photon Cloud application and getting an App ID.

## Voice & Chat

- [Voice Introduction](https://doc.photonengine.com/voice/current/getting-started/voice-intro): Real-time voice chat SDK for Unity.
- [Voice for Fusion](https://doc.photonengine.com/voice/current/getting-started/voice-for-fusion): Integrating Photon Voice with Fusion.
- [Voice for Quantum](https://doc.photonengine.com/voice/current/getting-started/voice-for-quantum): Integrating Photon Voice with Quantum.
- [Chat Introduction](https://doc.photonengine.com/chat/current/getting-started/chat-intro): Cross-platform text chat SDK.
- [Chat Features Overview](https://doc.photonengine.com/chat/current/getting-started/features-overview): Channels, private messages, status, and friends.

## Photon Server (self-hosted)

- [Photon Server in 5 Minutes](https://doc.photonengine.com/server/current/getting-started/photon-server-in-5min): Quick start for running the self-hosted Photon Server 5.
- [Photon Server Introduction](https://doc.photonengine.com/server/current/getting-started/photon-server-intro): Architecture and concepts of Photon Server.
- [On-Premises or SaaS](https://doc.photonengine.com/server/current/getting-started/onpremises-or-saas): Choosing between self-hosting and Photon Cloud.
- [What's in Photon 5](https://doc.photonengine.com/server/current/version-history/whats-in-photon-5): New features in Photon Server v5.

## API Reference (class & method docs — doc-api.photonengine.com)

Generated reference for SDK classes, methods, enums, and callbacks. This is a separate site from the guides above; the `.md` suffix and version/locale conventions do *not* apply here, and Photon notes the list may lag the newest SDKs. Use these when writing code against a specific type or signature.

- [API Reference Index](https://doc-api.photonengine.com/): Full list of all client and server API references.
- [Fusion API](https://doc-api.photonengine.com/en/fusion/current/index.html): Class/struct/enum reference for Fusion (Unity).
- [Quantum API](https://doc-api.photonengine.com/en/quantum/current/index.html): Reference for the Quantum simulation and runtime API.
- [.NET / C# Client API](https://doc-api.photonengine.com/en/dotnet/current/index.html): Realtime C# client — the base layer underneath most Photon SDKs.
- [C++ Client API](https://doc-api.photonengine.com/en/cpp/current/index.html): Realtime C++ client.
- [JavaScript / TypeScript Client API](https://doc-api.photonengine.com/en/javascript/current/index.html): Realtime web client.
- [Voice API](https://doc-api.photonengine.com/en/voice/current/index.html): Photon Voice reference.
- [Server API](https://doc-api.photonengine.com/en/server/current/index.html): Photon Server (self-hosted) reference.
- [Plugins API](https://doc-api.photonengine.com/en/plugins/current/index.html): Server-side plugin / webhook reference.
- [Analytics API](https://doc-api.photonengine.com/en/analytics-api/current/intro): Photon Analytics API.
- [PUN Client API](https://doc-api.photonengine.com/en/pun/current/index.html): Legacy PUN 2 client reference.

## XR / Industries

- [Extended Reality Overview](https://doc.photonengine.com/arvr/current/extended-reality-overview): Photon for AR/VR/XR multiplayer applications.
- [XR Addons Overview](https://doc.photonengine.com/arvr/current/xr-addons/xr-core/fusion-industries-addons-overview): Fusion Industries addons for XR (rig sync, connection management, content sync).

## PUN (legacy, maintenance mode)

- [PUN 2 Introduction](https://doc.photonengine.com/pun/current/getting-started/pun-intro): Photon Unity Networking 2 — legacy Unity netcode; new projects should use Fusion or Quantum.
- [PUN Basics Tutorial](https://doc.photonengine.com/pun/current/demos-and-tutorials/pun-basics-tutorial/intro): Classic PUN 2 beginner tutorial.

## Optional

- [Tournament SDK Overview](https://doc.photonengine.com/tournamentsdk/current/overview): SDK and dashboard for in-game tournaments.
- [Bolt Overview](https://doc.photonengine.com/bolt/current/getting-started/overview): Legacy Photon Bolt SDK (discontinued; superseded by Fusion).
- [Fusion 1 Documentation](https://doc.photonengine.com/fusion/v1/fusion-intro): Previous Fusion major version.
- [Quantum 2 Documentation](https://doc.photonengine.com/quantum/v2/quantum-intro): Previous Quantum major version.
- [Photon Server 4 Documentation](https://doc.photonengine.com/server/v4/getting-started/photon-server-intro): Previous Photon Server version.