Can I extend my ETA (subclass 601) or apply for another one?

An ETA is valid for 12 months and there is no facility to extend it. The 3-month-per-visit and 12-month validity limits are fixed.

When your ETA expires, you can apply for a new ETA if you are still eligible. If you need to stay in Australia for longer than the ETA allows on a single visit, you would generally need to apply for a different visa, such as a longer Visitor visa.

Because the ETA is for genuine short-term visits, repeatedly using it to live in Australia for extended periods is not its intended purpose.