We have migrated from ServiceStack to ASP.NET. Web API endpoints no longer accept HTTP Form requests; everything must be application/json. NOTE: Plugins that implement endpoints will also have to migrate.
Plugins must now target net5.0.
IHttpClient removal: Now inject IHttpClientFactory instead.
HttpException removal: Now catch HttpResponseException instead.
For the upcoming release of Jellyfin, there are some plugin ABI changes.
From the 10.7 RC1 Release Notes: