I knew I’d read about this recently - and there is a tool to flag your contacts so they don’t count when you get your next HubSpot renewal. It’s not quite an archive because they’re all still in your account - so you could argue it’s better than an archive. See https://www.hubspot.com/marketing-contacts/anz
According to the article, you can have up to 1 million contacts ‘for free’ - and only pay for those you market to.
And on further reading… Set contacts as marketing the small print says “Please note: this functionality is currently available on a limited basis for test users in the ANZ region.” So either the document is out of date - or anyone who needs this functionality needs to move to New Zealand 