Anthropic bought Stainless and shut its SDK generator. Cloudflare open-sourced Forge instead

Cloudflare has released Forge, an open source pipeline that turns an API definition into the SDKs, command-line tools, documentation and other interfaces developers use to work with a service.

Forge is licensed under Apache 2.0 and can be run and modified privately without paying Cloudflare. Dimitri Mitropoulos, Matt Taylor and Samuel MacLeod introduced it in a blog post published on Monday. It already generates the output required by cf, Cloudflare's unified command-line interface, while the company's API documentation and SDKs are due to move over in the coming months.

What Forge does

According to Cloudflare's blog, Forge runs in CI and generates SDKs, CLIs and documentation directly from API definitions.

The same code generators can be extended to produce Zod or Valibot schemas, MCP servers or Cap'n Web bindings, which let applications call remote services through Cloudflare's TypeScript-based RPC system.

When an SDK generator disappears

Forge arrives 11 days after Google said it had partnered with the API tooling company Speakeasy to open source the latter's OpenAPI code-generation suite under the AGPLv3 licence.

In a blog post published on September 17, Google said its SDK-generation provider had been acquired and "abruptly announced its shutdown" just as the company was preparing to launch a new API.

That provider was Stainless. Anthropic acquired the SDK and MCP tooling company on May 18, after which Stainless said it would wind down its products, including the generator that kept client libraries in step with changing APIs.

The New Stack reported at the time that customers including OpenAI, Google and Cloudflare kept the SDKs already generated for them but lost the service that updated them.

Speakeasy's suite covers SDK generators for seven languages, an agent-native CLI generator and a generator that turns documentation into an MCP server.

Why Cloudflare built its own

Cloudflare says it had relied on hosted generation products in production: "None of them solved this problem for us, and some have shut down entirely." Its API now spans more than 3,500 operations across hundreds of services maintained by different engineering teams.

The company wanted engineers to see what an API change would do to the resulting SDK, CLI and documentation before the code was merged, and wanted the same system to cover MCP servers and Cap'n Web bindings too.

Cloudflare CTO Dane Knecht told The New Stack that agents raise the stakes: "If that layer is stale or incomplete, an agent doesn't just have a worse developer experience, it can misunderstand what a service can do."

Forge still has much to prove: it is early and cf is its first production output. But within 11 days, two former Stainless customers put open source SDK generation at the centre of their API tooling.