This 92nd edition of the Kafka Monthly Digest covers what happened in the Apache Kafka community in September 2025.
For last month’s digest, see Kafka Monthly Digest: August 2025.
Releases
There is one new release, 4.1.0, and two releases are in progress, 4.0.1 and 4.2.0.
4.1.0
On September 2, after 4 release candidates, I published Apache Kafka 4.1.0. You can find the announcement on the Apache Kafka blog. You can also check the release notes and the release plan in the wiki.
Queues for Kafka (KIP-932) is now available in preview, but it's still not ready for production usage.
This release brings several major new features and improvements across all components.
Kafka brokers and clients
Updates to the Kafka broker and clients include the following:
- Many client-side plugins can now implement the
Monitorableinterface to register their own metrics. (KIP-877)
Kafka Connect
Updates to Kafka Connect include the following:
Kafka Streams
Updates to Kafka Connect include the following:
4.0.1
Another issue (KAFKA-19668) was found in RC1, so Christo Lolov published 4.0.1 RC2 on September 11. The vote is currently on-going. The release plan is available in the wiki.
4.2.0
On September 30, Christo Lolov volunteered to be the release manager for Kafka 4.2.0. The release is planned for January 2026. You can find the release plan in the wiki.
Kafka Improvement Proposals
Last month, the community submitted 10 KIPs (KIP-1211 to KIP-1221, KIP-1212 was skipped). I'll highlight a few of them:
- KIP-1214: Change log.segment.bytes configuration type from int to long to support segments larger than 2GB: At the moment the maximum segment size is 2GB. This KIP proposes allowing larger segment sizes. In some environments, this could help decrease the inodes and file descriptors usage, as well as the overhead of new segment rotations for high throughput topics.
- KIP-1217: Include push interval in ClientTelemetryReceiver context: With KIP-714 brokers can receive client metrics. However the context associated with client-side metrics does not indicate how often they are refreshed. This KIP proposes adding the metrics push interval as part of the context to make it easy for broker reporters to handle the lifecycle of client metrics and accurately delete stale client metrics.
- KIP-1219: Configurations for KRaft Fetch and FetchSnapshot Byte Size: A good network connection is necessary between members of a KRaft quorum. If a new follower has a slow network connection to the active controller, and if it is not able to complete a full fetch or fetch snapshot within the fetch timeout, 2 seconds by default, it may never be able to join the quorum. Currently the maximum fetch and fetch snapshot size is 8MiB. This KIP proposes making this limit configurable by introducing two new settings, controller.quorum.fetch.snapshot.max.bytes and controller.quorum.fetch.max.bytes, and lowering their default value to 1MiB.
- KIP-1221: Add application-id tag to Kafka Streams state metric: Kafka 4.0 added a number of new Streams metrics (KIP-1091). But when running multiple Streams instances it can be hard to clearly map each metric series to a Streams instance. This KIP aims at resolving this issue by adding a new tag,
applicationId, to these metric series.
Community Releases
- strimzi-kafka-operator 0.48: Strimzi is a Kubernetes Operator for running Kafka. This release adds support for Kafka 4.1.0. Each custom resource can now be monitored using kube-state-metrics (KSM). Users can also provide custom authentication plugins for integrating with third-party providers. The Strimzi Metrics Reporter can now be used with Kafka Connect, MirrorMaker and the HTTP bridge.
Blogs
I selected some interesting blog articles that were published last month:
