Apache Kafka 4.1.0 Released: What’s New and Why It Matters

The Apache Kafka community has officially released Kafka 4.1.0, bringing a wave of new features, security updates, and long-awaited improvements across the broker, clients, Kafka Streams, and Kafka Connect.

If you run Kafka in production—or you’re building real-time applications with it—this release is worth paying attention to. Let’s break down the highlights and what they mean for you.

Key Highlights in Kafka 4.1.0

Here are some of the standout changes in this release:

• Connector Multiversioning – Run multiple versions of the same connector or plugin side-by-side. This makes upgrades, rollbacks, and compatibility testing much easier in Kafka Connect.
• Smarter Consumer APIs – New Consumer#close options let you choose whether to leave a consumer group or stay in it when closing, improving flexibility for controlled shutdowns.
• Transactional Improvements – Kafka now supports transactional ID filtering in the ListTransactions API, along with stronger protections against producer epoch and fencing issues.
• Controller & Broker Enhancements – The controller now tracks broker lifecycle events, helping operators better monitor cluster stability. High-watermark replication has also been made explicit for more reliable recovery.
• OAuth & Security Updates – OAuth support gets stronger with jwt-bearer grant type, clearer documentation, and improved error messages. Plus, two CVEs have been patched (commons-beanutils, commons-lang).
• Kafka Streams Upgrades – More metrics for cooperative rebalancing, better join handling, and internal topic naming improvements (KIP-1111).
• Stability Everywhere – Hundreds of fixes for transaction deadlocks, metadata sync delays in KRaft, and flaky tests make this a safer upgrade.

New Features Worth Noting

1. Connector Multiversioning
   Kafka Connect can now handle multiple versions of the same connector class at once. For example, you could run two versions of the Debezium connector in parallel during an upgrade.
2. Consumer Close Options
   Previously, calling Consumer#close always meant leaving a consumer group. Now, you can choose to make controlled deployments smoother.
3. Transactional Improvements
   With new filters in the ListTransactions API and explicit high-watermark replication, transaction handling is more robust than ever.
4. Metrics & Monitoring
   Kafka Streams and group coordinators expose more useful metrics, giving you better visibility during rebalances and cooperative consumption.

Security Fixes

Two security patches were shipped in this release:

• CVE-2025-48734 → Fixed commons-beanutils vulnerability
• CVE-2025-48924 → Upgraded commons-lang dependency

If you operate Kafka clusters in production, upgrading to 4.1.0 helps close these gaps immediately.

Improvements & Bug Fixes

• Transaction deadlocks resolved
• Faster metadata updates in KRaft
• Cleaner API surface – Deprecated APIs like Records#downConvert and old broker metadata classes have been removed.
• Streams stability – Fixes for join consistency, rebalance edge cases, and state restoration bugs.
• OAuth enhancements – Better integration with JWT-Bearer and improved error reporting.

Upgrade Notes

Before upgrading to Kafka 4.1.0, keep these in mind:

• Review your Connect plugins—if you’re using multiversion support, double-check configs.
• Watch for deprecated APIs—some older ones are now removed.
• Upgrade your security dependencies immediately to patch the CVEs.
• Test Streams apps in staging, since rebalance and join behavior have subtle changes.

Conclusion

📖 You can dive deeper into the official Kafka documentation for all the details.