Yeah, I worked with the Flickr team on that project. Scaling to billions of photos, with partial update support of popularity for ranking.

Back then, the properties had to stand up their own Vespa cluster(s), later on we created a managed service out of it. And, yes, the original plan for Vespa was to be a Vertical Search Platform, that is where the name Vespa comes from. More on the history in this blog post https://blog.vespa.ai/vespa-is-becoming-its-own-company/