API Update: Introducing the 'pool' field to the ws subscription response

At BitMEX, we are committed to continually improving our platform and infrastructure to support advanced trading capabilities for our users. As part of this ongoing effort, we are announcing an update to our WebSocket API subscription responses.

From 19 May 2026, a new field, pool, will be added to the following BitMEX WebSocket API subscription responses. The field will be populated when the user gets a subscription response.

Affected WebSocket feeds:

• orderBookL2

• orderBookL2_25

• orderBookL2_100

• orderBook10

• quote

• quoteBin1m

• quoteBin5m

• quoteBin1h

• quoteBin1d

• trade

• tradeBin1m

• tradeBin5m

• tradeBin1h

• tradeBin1d

Effective Date and Time: 19 May 2026, 06:00 - 09:00 UTC

This will be available in BitMEX Testnet from 13 May 2026 from 06:00 - 09:00 UTC.

What is Changing?

A new field, pool, will be added to the response of the WebSocket API listed above.

Please refer to the example WebSocket API response below:

ws connect: wss://www.bitmex.com/realtime

send: {"op":"subscribe", "args": ["orderBookL2:ETHUSDT"]}

response:

{ "success": true, "subscribe": "orderBookL2:ETHUSDT", "request": {"op":"subscribe", "args": ["orderBookL2:ETHUSDT"]}, "pool": "Secondary" }

Why are we making this change?

The addition of the pool field is necessary to facilitate protected order books, which are designed to maintain tighter spreads and deeper liquidity for a subset of traders. This field indicates which pool a given subscription belongs to.

This is an additive change, meaning it introduces a new field without removing any existing data. Most integrations should be unaffected.

If you have any questions about these upcoming changes, please contact Support.

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In the meantime, if you have any questions please contact Support who are available 24/7.