.NET 8 and .NET 9 both reach end of support on November 10, 2026, so teams that hopped from 8 to 9 for extra time gained none.
Retargeting to .NET 10 is usually a one-line project change, and .NET 10 is supported as LTS until November 10, 2028.
The real cost is tooling: Visual Studio 17.14 is the minimum to load the .NET 10 SDK, and targeting `net10.0` needs Visual Studio 2026.