OpenAPI 4 is the evolution of the most widely used standard for describing REST APIs. This version introduces significant changes to format, data types, and composition capabilities.
What's new in OpenAPI 4
OpenAPI 4 adopts JSON Schema 2020-12 as the basis for schema description, replacing earlier JSON Schema versions. This unifies data validation between API specification and data schemas.
Automatic linting and validation: the new specification includes stricter validation rules that detect inconsistencies before deployment. Tools like Redocly, Spectral, and Stoplight already support OpenAPI 4.
Enhanced composition: $ref and reusable components have been improved with support for polymorphism, more expressive oneOf/anyOf, and schema inheritance.
Practical benefits
With OpenAPI 4, you can generate clients in 40+ languages, interactive documentation (Swagger UI, Redoc, Scalar), contract tests, and server mocks. TypeScript type generation from the specification eliminates duplication between documentation and implementation.
Ecosystem tools
Tools like openapi-typescript generate complete types. OpenAPI-Generator produces SDKs. Zod can validate requests against OpenAPI schemas at runtime.
OpenAPI 4 makes designing, documenting, and maintaining APIs easier than ever. At Vynta, we apply OpenAPI 4 in all our API projects to guarantee consistency and ease of integration.