Speakeasy Publishes Comparison of OpenAPI SDK Generators

Speakeasy published a detailed comparison of five OpenAPI SDK generators, evaluating how they handle code generation across languages, type safety at runtime, dependency size, and support for air-gapped deployment. The results matter for teams that need predictable client library generation from API specifications.

The comparison reviews Speakeasy, Stainless, Fern, APIMatic, and OpenAPI Generator across criteria including language coverage, runtime type safety, dependency footprint, OpenAPI fidelity, enterprise features, and deployment flexibility. It also assesses which generators can operate without connectivity and how closely they align with OpenAPI as the specification input.

Speakeasy supports 10 languages, uses Zod for runtime type safety, and ships TypeScript SDKs with a single runtime dependency. It treats OpenAPI as the single source of truth and runs as a standalone CLI binary for air-gapped environments. Stainless supports seven languages and relies on a custom configuration DSL; its TypeScript casting does not include runtime validation, and its Cloudflare SDK includes more than 25 dependencies.

Fern supports seven languages and generates SDK and API reference documentation, built on a proprietary DSL with OpenAPI supported as an import format. It offers TypeScript SDKs as Node.js-only, with OAuth 2.0 available only on paid plans, and it requires entry pricing of $250 per month per SDK. APIMatic supports seven languages, includes a developer portal product, and has TypeScript SDKs with more than 40 dependencies; OpenAPI Generator supports more than 50 language targets and is positioned as the free, open-source option.

“SDK generation has moved from a developer convenience to a piece of enterprise infrastructure that security, compliance, and platform teams all care about,” said Sagar Batchu, CEO and co-founder of Speakeasy. “The differences between generators now show up in SOC 2 audits, supply chain reviews, and developer adoption curves. We built Speakeasy to be the SDK generator that holds up to enterprise scrutiny: runtime type safety, minimal dependencies, OpenAPI as the single source of truth, and a binary you can run inside any environment.” Of the five platforms evaluated, Speakeasy and OpenAPI Generator support fully air-gapped SDK generation, while Stainless, Fern, and APIMatic require connectivity to vendor-hosted services.