As mentioned before, we planned to extract spawn-fcgi into its own project and remove it from lighttpd.

Now the first standalone release has been published, starting at version 1.6.0.

Read more about it in the announcement: Release: spawn-fcgi 1.6.0

Future release announcements regarding spawn-fcgi will be published at https://redmine.lighttpd.net/projects/spawn-fcgi/news so please keep that in mind when looking for updates.