Ably is a hosted realtime network, and it's very good at moving messages between clients at scale. Air Pipe covers the same realtime fundamentals — WebSocket and MQTT pub/sub, presence, history-rewind and retained messages — and adds the thing a relay can't: the same connection runs your pipeline on each message, with your own logic as the channel ACL.
Wildcards, presence, message history-rewind and retained values all live in the WebSocket channel API, with global reach across geo-routed nodes. MQTT reaches the same delivery guarantees the native broker way — persistent sessions, QoS 1/2 and retained. You're not trading away realtime features to get the rest.
A relay moves bytes between clients and stops there. Air Pipe can run your config on each message before it fans out — assert on it, transform it, write it to Postgres or MongoDB, call an upstream API — and gate each channel with your own pipeline logic against the user's JWT claims. The realtime layer and the backend are the same thing.
With a relay you still bring your own backend, your own auth service and the glue between them. Air Pipe is transport, per-user auth, the compute that runs on each message, and billing in one product — metered in the same request units as everything else you run, which roll over for 12 months.
Run realtime on our managed cloud, or self-host the same single binary on your own infrastructure — nothing-shared either way, with no external broker or Redis to operate. Self-hosted realtime connections aren't billed.
If you need a battle-tested global realtime network at very large connection counts, with the SLAs and edge footprint of a dedicated provider, Ably is built for exactly that and we don't claim to out-scale it. Air Pipe fits when realtime should be part of your backend — messages that run your logic, channels gated by your auth, on infrastructure you can own — rather than a relay you wire a backend behind.