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That is probably exactly why they are using it ... you don't get to 250k lines of code overnight.

My understanding is that the company is a few years younger than Spec, but perhaps the code base is very very old.

Schema is a good library. Everyone seems to use spec today, but Schema easier to use than spec IMO.

Spec is also still in alpha, with spec2 still under development.

We used clojure.spec in production for years. "Alpha" just means the API could change.