The 3.9.0 release is a new feature release with the following highlights:

• RFC 96: Deferred C++ plugin loading
• RFC 97: OGRFeatureDefn, OGRFieldDefn and OGRGeomFieldDefn "sealing"
• RFC 98: Build requirements for GDAL 3.9
• RFC 99: Geometry coordinate precision
• Add S104 (Water Level Information for Surface Navigation Product) and S111 (Surface Currents Product) raster read-only drivers (required libhdf5)
• Add raster GTI (GDAL Raster Tile Index) driver to support catalogs with huge number of sources.
• Add vector MiraMonVector read/creation driver (#9688)
• Deprecated ARG driver has been removed (#7920)

and many other enhancements and fixes as detailed in the release notes