After Message Queue for MQTT is upgraded from V2.x.x to V3.x.x, it implements independent data storage and eliminates its messaging dependency on Message Queue for Apache RocketMQ. Therefore, the usage of Message Queue for MQTT instances and topics has changed.

Resource V2.x.x usage instructions V3.x.x usage instructions
Message Queue for MQTT instance A Message Queue for MQTT instance of version V2.x.x must be bound to a Message Queue for Apache RocketMQ instance before the instance can work normally. A Message Queue for MQTT instance of version V3.x.x does not need to be bound to a Message Queue for Apache RocketMQ instance to publish and subscribe to messages.
Message Queue for MQTT Topic Parent topics of a Message Queue for MQTT instance of version V2.x.x are the topics of Message Queue for Apache RocketMQ. You can use the Message Queue for Apache RocketMQ console or call an API to create topics for Message Queue for MQTT. In Message Queue for MQTT of version V3.x.x, you must use the console or API of Message Queue for MQTT to create topics.
Message Queue for MQTT instance endpoint An endpoint of a Message Queue for MQTT instance of version V2.x.x must be bound to a Message Queue for Apache RocketMQ instance before you can obtain the endpoint in the Message Queue for MQTT console. In Message Queue for MQTT of version V2.x.x, you do not need to bind the endpoint to a Message Queue for Apache RocketMQ instance to obtain the endpoint in the Message Queue for MQTT console.
Message Queue for MQTT rule No rules are required. V2.x.x versions of Message Queue for MQTT share topics with Message Queue for Apache RocketMQ. If you need to exchange data with other Alibaba Cloud services (Message Queue for Apache RocketMQ is supported only), you must create a rule in the Message Queue for MQTT console or call the OpenAPI of Message Queue for MQTT.

Resource usage is highly related to billing. After the upgrade, Message Queue for MQTT topics of V3.x.x do not incur fees, but the rest billing items remain unchanged. This change saves your cost for the original Message Queue for Apache RocketMQ topics. For more information about the billing methods, see Billing methods.