I believe their recent Usage page change enabled this. I can’t find the blog post at the moment, though.
Ah, here we go…
New ways to understand API usage and manage API keys
We are launching two platform improvements to give developers both more visibility into their usage and control over API keys.
First, developers can now assign permissions to API keys from the API keys page. For example, a key could be assigned read-only access to power an internal tracking dashboard, or restricted to only access certain endpoints.
Second, the usage dashboard and usage export function now expose metrics on an API key level after turning on tracking. This makes it simple to view usage on a per feature, team, product, or project level, simply by having separate API keys for each.