On master with this commit it has now been reduced to 1 thread! This makes ServerSocketReceiver and ServerSocketAppender unusable as each will use the single thread to listen for clients leaving no threads for the clients themselves.

The release news associated with this commit is:

Logback's internal <code>ThreadPoolExecutor</code> now has an initial pool of 1 thread instead of 8 previously.

This appears to be a misinterpretation of ScheduledThreadPoolExecutor's behaviour. Reading the Javadoc it sates that it acts as a fixed sized thread pool. This type of executor doesn't seem appropriate for use in this case.