This is one of the genuinely unsettled questions in US expat tax: the IRS has never published guidance squarely addressing superannuation, and the US-Australia treaty does not clearly cover it. Practitioners commonly treat employer contributions and fund earnings as taxable to US persons under one of several theories (employees' trust, foreign grantor trust), and positions vary between firms.
What is certain is the reporting: super balances count toward FBAR and Form 8938 thresholds, and some structures raise Form 3520 questions. If super is a large share of your wealth, this is a question for a preparer who will put their position in writing, not a checkbox.