I tried to message to Stolze but I'm not sure if he received.
Regardless, my understanding as of now and reinforced by other uses on this forum is that as soon as an Active log is filled, (regardless as to whether or not it has committed/uncommitted/rolledback transactions) that log file is archived.
However, Stolze stated the following in this thread:
A log file is only archived if it doesn't contain stuff from a transaction that is not yet committed/rolled back. Such a log file is active. Log files that don't contain stuff from running transactions anymore are not active and can be archived. Now, if I have a long running transaction that did some INSERTs that were logged in the first log file, that file cannot be archived. Let's assume that some more transactions (or even the same one) cause log files 2..10 to be used. Even more operations requiring to be logged give us the "when needed" situation: another log file is needed and then a secondary log file is created.