Do you use JSON Schema in production?

I use it heavily in all my projects.

- (indirectly) as part of OpenAPI Spec

- storing and versioning schemas for JSONB data in Postgres, which is useful when deserializing

- (indirectly) in my IDE to give me hinting/linting for my JSON-based config files

- for form definitions (JSONForms, React JSON Schema Form)

No.

I looked at it previously but it's not a very developer friendly way to specify an API.

I use gRPC.

They both support code generation for numerous languages. gRPC is arguably more performant.