The trailer basically sort of confirms the US format for Australia. It doesn't say so directly, but refers to "Big Brother 2.0", says things like "evict your friends" or "Control. Evict. Win" and apart from a few scenes at the beginning only features scenes from Big Brother US and Big Brother Canada like nominations and competitions.
According to TV Black Box they state "In what will be a major break with tradition, the entire series will finish shooting before the first episode airs. As part of this change in production there will be no live voting from the public, instead housemates will vote against each other and there will be no live elimination episodes."
They go on claim that shooting will be begin in April but the series will not air until August, after the 2020 Tokyo Summer Olympics.
https://7news.com.au/entertainment/tv/confirmed-big-brother-will-return-to-australian-tv-in-2020-c-518757