Release 26.0.0 is the first release in the Horizon 26 series.
It contains a large number of bug fixes and new features, most notably initial support for handling the BGP Monitoring Protocol in Telemetryd.
For a high-level overview of what has changed in Horizon 26, see What’s New in OpenNMS Horizon 26.
The codename for 26.0.0 is Balaclava.