Why upgrade now

November 10, 2026 is the end-of-support date for both .NET 8 and .NET 9. Your apps keep running after that date, but they stop receiving security patches, so every new vulnerability stays open. The target is .NET 10, the current LTS release, supported until November 2028 ( Microsoft .NET Blog ).

The good news: for most apps on modern .NET this is a days-long job, not a months-long one. The breaking changes are targeted and documented, and most of them show up as compiler warnings. This checklist is the order I'd follow for a typical solution, plus the changes most likely to bite.

Before you start

Take inventory first, retarget second.…