Cloudflare Open-Sources Forge, an Apache 2.0 SDK and CLI Generator, as Anthropic Winds Down Stainless's Hosted Product
Cloudflare released Forge, an Apache 2.0 pipeline that turns OpenAPI specs into SDKs, CLIs and docs, after Anthropic said it would wind down Stainless's hosted SDK generator.
Editor's Note ·
- Clarification:
- The article says the link between Forge and the Stainless wind-down comes only from The New Stack's headline and framing. In fact the body of The New Stack article argues that the Stainless wind-down "goes some way toward explaining why Cloudflare is making Forge open source", and notes that Cloudflare "doesn't name it specifically". Cloudflare's own blog post does not mention Stainless or Anthropic; it says only that "some [hosted products] have shut down entirely."
- Clarification:
- The headline's "as Anthropic Winds Down Stainless's Hosted Product" does not convey timing. TechCrunch reported the Anthropic acquisition and the plan to wind down Stainless's hosted products on May 18, 2026, more than four months before Cloudflare released Forge on September 28, 2026.
Overview
Cloudflare has released Forge, an open-source pipeline for generating SDKs, command-line tools, documentation and other artifacts from API definitions. According to the Cloudflare Blog post published on September 28, 2026, the tool is “available open source under the permissive Apache 2.0 license.” The release drew attention because The New Stack framed it as Cloudflare’s answer to the shutdown of Stainless’s SDK generator after Anthropic bought the company.
What We Know
What Forge is
The project’s GitHub repository describes Forge as “a schema-first OpenAPI code generation and surface tooling framework.” It uses a plugin-based architecture to resolve OpenAPI 3.x specifications, apply JSONPath-based overlays, and generate typed SDKs, CLI interfaces, runtime helpers and documentation, per the same repository page.
The repository states that the project is in early development and is currently focused on the cf CLI as its primary output. Support for TypeScript, Go, Python, Terraform and documentation targets is to be developed alongside Cloudflare’s own SDK releases, according to the GitHub repository. The Cloudflare Blog lists upcoming SDKs for TypeScript, Rust, Python, Go, PHP and Terraform.
Why Cloudflare built it
The Cloudflare Blog says: “We built Forge because we needed it ourselves in order to treat agents as our customers.” The post describes the scale of the problem: “Cloudflare’s API has over 3,500 operations, and the hundreds of services that power these APIs are written in many languages, including Rust, Go, TypeScript, and Python.”
The post also says that previously used hosted solutions proved inadequate, and that product changes sometimes broke generation pipelines and caused problems at release time. Forge instead runs inside a team’s own CI pipelines, per the same post.
Design choices
Cloudflare describes the tool’s preview behavior as “a full preview build for every change, but applied to SDK generation at scale, including when the API surface is distributed across hundreds of services and repositories,” according to the Cloudflare Blog. Forge supports chaining transformers, so the output of one stage can feed others, and OpenAPI is the input format today, with AsyncAPI, GraphQL, Cap’n Proto and Protobuf planned, the post says.
The pipeline also generates bindings for Cap’n Web, which the post describes as Cloudflare’s RPC system that lets TypeScript call remote APIs as local methods.
The Stainless backdrop
As reported by TechCrunch, Anthropic acquired Stainless, a New York startup founded by former Stripe engineer Alex Rattray, whose software converts API specifications into SDKs in languages including Python, TypeScript, Kotlin, Go and Java. TechCrunch lists OpenAI, Google, Replicate, Runway and Cloudflare among its customers. Anthropic said it would “wind down all hosted Stainless products, including its SDK generator,” while existing customers keep ownership of SDKs already generated, per TechCrunch. Anthropic did not disclose terms; TechCrunch cites The Information as reporting a valuation above $300 million.
The New Stack’s headline puts the two events side by side: “Anthropic bought Stainless and shuttered its SDK generator. Cloudflare open-sourced Forge instead.”
What We Don’t Know
- Whether Cloudflare’s blog post positions Forge as a direct replacement for Stainless is not stated in the sources reviewed; the link between the two events comes from The New Stack’s framing.
- The repository describes Forge as early-stage, and the sources do not give dates for the additional language targets beyond “upcoming.”
- Whether other former Stainless customers will adopt Forge is not reported.
Analysis
The release shifts one piece of API tooling from a hosted product into infrastructure that teams can run and modify themselves. Cloudflare’s own account is that scale and coordination across hundreds of services drove the decision. Because Forge is in early development, with the cf CLI as its main output so far, its breadth relative to the hosted generator it is being compared with remains to be shown.