What it is and why

Writers and listeners do not open a peer connection. Each side grabs a nearby FastPubSub edge. The overlay carries live messages between regions.

Message model:

• One overlay frame is about 64 KB (a datagram). Bigger app blobs: FragmentFilter in the SDK.
• Nothing hits disk on the hot path.
• No global order. Two messages can arrive swapped.
• Address is overlay + tenant + channel.

Where it earns its keep:

• Keeping a path. Cable cut. Bad ISP. Dying relay. The mesh measures another route. A few samples can vanish while it switches.
• Fan-out. One publisher, many subscribers. You do not hold a socket to each client.
• Small client code. Access token, then publish/subscribe. The SDK picks an edge. You skip running a worldwide WebSocket fleet.

What it is not:

• A durable log. Keep Kafka / NATS JetStream / RabbitMQ if you need that.
• A file CDN. No object cache. No big HTTP files. Same shape as a CDN for live traffic: nearest edge, measured backbone, fan-out to people who are connected now.
• A VPN or raw IP overlay you sell to customers.
• A broker you install yourself.

Need replay? Sit your own broker next to FastPubSub (subscribe, persist, republish). Or wait for the open-source FastPubSub broker. Until then this product stays online-only.

Where to go next

• Delivery semantics — drops, duplicates, ordering, join window
• Quickstart — Cockpit, token, SDK
• Try the demos — Paint Board, Online Radio, Video Meeting