.NET Core 3.0 will reach end of life on March 3, 2020. It is a “Current” release and is superseded by .NET Core 3.1, which was released on December 3, 2019. After that time, .NET Core patch updates will no longer include updated packages .NET Core 3.0.
.NET Core 3.1 is a long-term supported (LTS) release (supported for at least 3 years).