Australia’s Online Safety Act 2021 was amended in late 2024 to introduce a minimum age regime for online platforms, now in force as of December 2025, requiring certain services (especially social media) to take reasonable steps to prevent under‑16s from accessing them. To comply, platforms must implement age assurance measures, which can include things like age checks or verification flows.

Substack has chosen to apply age verification for Australian users in response to those requirements, even though it isn’t explicitly listed among the core “social media” platforms the law targets...

Many analysts view Substack’s approach as an overly cautious interpretation of the law, or even pre‑emptive compliance, because Substack isn’t explicitly on the list of platforms covered by the age restriction.