Social media platforms captured under a world-leading ban were not assessed based on the harm they pose to under-16s, Australia's eSafety commissioner says.

They were instead assessed on whether their "sole or significant purpose" was social interaction, which leaves popular gaming platform Roblox exempt for now.

"If the online gameplay is the significant or sole purpose, if that were taken away, would the kids still use that messaging functionality to chat?" eSafety Commissioner Julie Inman Grant told reporters in Canberra on Wednesday.

"Probably not."

A month out from the ban coming into effect, the Albanese government on Wednesday announced the list of platforms it captures has been expanded to include the forum website Reddit and live-streaming platform Kick.

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