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The table lists limits that apply to Pub/Sub brokers and clients during the beta release.

ItemLimit Notes
Namespaces per Account3The maximum number of namespaces allowed on an account.
Brokers per Namespace3Can eventually be increased.
Subscribers per topic1000The maximum number of subscribers per MQTT topic.
Connections per Device1The number of simultaneous connections from a single client ID (or token). More than one connection from the same client ID will result in existing clients receiving a DISCONNECT using Reason Code 0x8e (Session Taken Over).
Maximum Packets per Second per Client10The number of MQTT packets per second a client can send to the broker.
Clients that exceed this rate will receive a DISCONNECT with Reason Code 0x96 (Message rate too high).
Maximum Topic Length65k bytesThe maximum length of a topic, in bytes, including all slashes, prefixes, or wildcard symbols.
Maximum Topic Depth8The maximum number of forward slashes (/) allowed in a topic.
Maximum Message Size64KBIncludes metadata such as client ID, additional metadata fields, and optional MQTT fields.
Maximum Client ID Length23 bytesThe maximum length of an MQTT Client Identifier in bytes.
Client IDs must also be at least 1 byte long per the MQTT standard. Shorter client IDs are rejected with a CONNACK using Reason Code 0x85 (Client Identifier not valid).
Maximum Username Length32 bytesThe maximum length of the username in bytes.
Usernames are optional, but if provided, must match the Client ID.
Invalid usernames are rejected with CONNACK using Reason Code 0x86 (Bad Username or Password).
Maximum Password Length4,096 bytesThe maximum size of the UTF-8 encoded password, in bytes.
Invalid passwords are rejected with CONNACK using Reason Code 0x86 (Bad Username or Password).
Connect Interval10 secondsMaximum interval that a client can wait between establishing TLS connection and send a CONNECT.
Clients that take longer than this will be disconnected.
Minimum Keep Alive Interval10 secondsMinimum time interval in which a client must send an MQTT control packet or a PINGREQ packet.
Clients that take longer than this will be disconnected.
Maximum Session Expiry Interval7 daysMaximum time interval to retain a client’s session state. Currently includes Subscriptions and Will messages.
Note that 7 days is best effort, and in some cases, the session state may be shorter.
Maximum Number of Revoked Credentials per Broker10,000The maximum number of credentials that can be revoked for a single broker.

Storage and network units are in SI units.