Release 27.0.1 is the second release in the Horizon 27 series.
It contains a number of bugfixes including a critical CVE fix for Jetty, as well as a number of other smaller changes and improvements.
For a high-level overview of what has changed in Horizon 27, see What’s New in OpenNMS Horizon 27.
The codename for 27.0.1 is Pan-Galactic Gargle Blaster.