Are you trying to be deliberately obtuse? Obviously, you can fudge the number with assumptions around churn rates/etc, but of course an investor would want a view of the rough 12m state of the business.
...which is why we have GAAP-recognized metrics, right? To prevent fudge-ability? And those metrics.. they're deliberately not publishing? Makes you think.
GAAP is basically a standards body to recognize practices.
When there are interesting stories that can't be told with GAAP metrics, accountants derive new metrics. Just because they haven't gone through the standardization process yet doesn't mean they're bullshit - investors in Anthropic can hire auditors to ensure the Anthropic metrics are still meaningful. There are a very small number of deep pocketed investors in Anthropic - they're not a public company like Enron trying to sell to the WSB crowd, or like 2007 CDOs being sold to dentists.
And run rate has been a widely recognized metric for SaaS as long as it has existed - it has meaning and can be audited.