There is an initial 1-hour round (coding/generic software skills) by an external company, followed by 5 rounds with Atlassian (2 coding, 1 system design, 2 soft skills).

I received feedback after the 2 coding rounds and then after the full process.

Regarding questions, go through the subjects listed in the other interview reports here on Glassdoor.

It's a lengthy process, but be prepared to be rejected after the full run, even if, according to the feedback, the problematic parts were in the earlier stages. It seems Atlassian performs a full review of performance only after the last round.