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Flash streams over a single WebSocket endpoint. Open one connection, then subscribe to the channels you need; they multiplex over the same socket. Endpoint: wss://flash.definitive.fi/v1/ws

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Channels

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Authenticating

There is no connect-time handshake. Authenticate in-band by including your Flash API key as apiKey in every subscribe message. Get a key from Become an Integrator. A connection is pinned to one portfolio on first successful auth, and to one API key once a channel is active. A subscribe with a different key on the same socket is rejected with UNAUTHORIZED and the connection is closed.

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Subscribing

Send a subscribe message for each channel as soon as the connection opens. Channel-specific fields are documented on each channel’s page.
Every accepted subscribe and unsubscribe is confirmed with an ack listing the connection’s active channels:
Stop a channel with an unsubscribe message on that channel. The server re-acks your remaining channels.

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Connection limits

The per-key connection limit is at least 50, pooled across everything using that key. If you need it raised, reach out. Exceeding it is rejected with CONNECTION_LIMIT and the connection is closed; a backed-off reconnect recovers as slots free. Channel-specific limits, like the quote subscription cap, are documented on the channel’s page.

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Heartbeats

Subscribe to heartbeats on every connection to receive a keep-alive frame once per second:
Each frame carries an incrementing counter and a timestamp:
Heartbeat frames need no action. They give a quiet connection two things: liveness detection (a gap in them means the connection is unhealthy, so reconnect rather than waiting) and steady traffic through any intermediary that closes idle connections on its own timeout.

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Reconnecting

  • On disconnect, reconnect with capped backoff and jitter, then re-subscribe to your channels. Nothing survives a disconnect: orders subscriptions return a fresh snapshot, and quote sessions cannot be resumed.
  • On UNAUTHORIZED, stop reconnecting and check your API key; reconnecting with the same key will not authenticate.
  • Other closes, including CONNECTION_LIMIT, are safe to retry with backoff.
  • If a stream stays unavailable, fall back to polling its REST counterpart.

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Errors

Errors arrive as a frame you can act on:
These codes can occur on any channel: Channel-specific codes are documented on each channel’s page.

Orders channel

Stream open orders in real time, for one funder or all of them.

Quotes channel

Stream live quotes for a market-order request.