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RabbitMQ 4.4.0 Adds Delayed Messages for Quorum Queues and Unix Domain Socket AMQP Listeners

RabbitMQ 4.4.0, released October 19, adds delayed delivery on quorum queues, a v2 classic-queue file format that blocks downgrades, and stricter OpenID Connect discovery checks.

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Overview

The RabbitMQ project published version 4.4.0 of its message broker on October 19, 2026, describing it in the release notes as “a new feature release.” The headline additions are delayed message delivery for quorum queues and support for binding AMQP listeners to a Unix domain socket. The release also carries several compatibility changes that operators should review before upgrading.

What Is New

Delayed messages on quorum queues

According to the 4.4.0 release notes, quorum queues now support delayed messages. A message with an x-opt-delivery-time annotation or header set to a future time, in milliseconds since the Unix epoch, is routed and enqueued immediately but only delivered to consumers once that time is reached. AMQP 1.0 clients set it as a message annotation and AMQP 0-9-1 clients as a long header. An AMQP 1.0 consumer can also delay redelivery of a message by setting the same key in the annotations of a modified outcome.

Unix domain sockets and connection limits

The release notes state that AMQP listeners can now bind to a Unix domain socket using the same listeners.tcp.* settings as a TCP listener, with the example listeners.tcp.1 = unix:/var/run/rabbitmq/rabbitmq.sock:0. The notes also list new rabbitmq.conf settings that limit concurrent client connections for the stream protocol (stream.max_connections), MQTT (mqtt.max_connections) and STOMP (stomp.max_connections). The existing connection_max and channel_max keys were renamed max_connections and max_channels, and the original names are still supported.

AMQP 1.0 and queue features

Per the release notes, AMQP 1.0 clients can request sole (exclusive) ownership of a container ID under the AMQP 1.0 Connection Uniqueness protocol extension. Two new commands, rabbitmqctl sole_connection_status and rabbitmqctl sole_connection_force_delete, manage such connections. Other additions listed include:

  • An optional x-name-prefix queue argument that sets the prefix for server-named queues, capped at 64 bytes, with amq.gen remaining the default. The notes say this is specific to AMQP 0-9-1.
  • An x-stream-initial-offset argument that lets a stream start at an offset other than 0.
  • Stable routing for x-modulus-hash exchanges: assuming a topology that does not change, messages carrying the same routing key are routed to the same bound destination. The notes say the exchange type moved from rabbitmq_sharding to the core.
  • A delivery-limit policy change that now takes effect for existing quorum queues. When the policy is removed the queue returns to the default limit of 20.

Plugins

The release notes say the MQTT retained message store now has per-virtual host limits on the number of retained messages and their total size, with defaults of 100,000 messages and 1 GiB. They also say the STOMP plugin is now a standalone protocol implementation that is no longer built on AMQP 0-9-1, following AMQP 1.0 and MQTT in previous years.

Upgrade Considerations

The release notes flag several items that can affect an upgrade:

  • The classic queue shared message store gained a new v2 on-disk file format (.sqs). New files are written in v2 automatically, existing v1 files (.rdq) are left as-is, and a node with v2 files present cannot be downgraded to 4.3.x or earlier.
  • OpenID Connect discovery responses are validated more strictly. A deployment whose identity provider serves non-HTTPS endpoints, or whose issuer claim does not match the discovery endpoint used to retrieve it, will fail discovery validation after the upgrade. The notes say this is known to affect Cloud Foundry UAA and name the settings auth_oauth2.discovery.verify_issuer and auth_oauth2.discovery.verify_https_endpoints as the way to opt out before upgrading.
  • GET /api/auth/hash_password/{password} was replaced with POST /api/auth/hash_password, which consumes a JSON document with one key, {"password": "..."}.
  • A passive declaration of a queue or exchange now requires any one of the configure, write or read permissions on that queue or exchange.
  • Several AMQP 0-9-1 headers that carried AMQP 1.0 message sections, such as x-amqp-1.0-properties, are no longer parsed. The notes say only a message stored by a 3.13 or earlier node and not read since carries them.

On Erlang, the 4.4.0 notes say the version fully supports the Erlang 28 and 29 series for both new clusters and rolling upgrades. They add that if RabbitMQ is upgraded to 4.4.0 and Erlang to 28 or later at the same time, the project highly recommends first upgrading to 4.3.7 or a later patch.

The project then published RabbitMQ 4.3.7, which it describes as “a maintenance release in the 4.3.x release series.” Its notes say that classic queue expiration (x-expires) timestamps were lost on node restart, so the queue TTL timer did not fire when it was supposed to if the TTL outlived the restart. The 4.3.7 notes also describe a new consumer_timeout_response setting; its default, notify_consumer, sends basic.cancel to clients that support the consumer_cancel_notify capability and closes the channel for others.

What We Don’t Know

The release notes are the only source reviewed for this article. They do not include benchmark figures for the quorum-queue or classic-queue changes, and they do not state an end-of-support date for the 4.3.x series. Production behavior of the delayed-message feature at scale has not been independently reported.