Stainless alternatives after the Anthropic wind-down (2026)
Last updated: September 2026
If your SDKs were generated by Stainless, look first for an alternative that can regenerate them without renaming a single method your users already call. For most teams, that means starting from the stainless.yml you already have, not from a blank config.
This page is written by Scalar, and Scalar sells an SDK generator, so read it with that in mind. Every claim about another product links to that vendor's own site, docs or repository, checked on September 26, 2026. We put ourselves first because it is our page. We also say where each option beats us.
Start with the file you already have. Scalar reads stainless.yml directly. Import it together with your OpenAPI document, and your resources, method names, pagination and package names carry over. Then diff the generated api.md against your current one. The Stainless migration guide walks through each step. For the full background (what Stainless announced, what keeps working, and every config key that does or does not carry), read the Stainless wind-down write-up.
Why teams are leaving Stainless
Nobody is leaving because the SDKs got worse. On May 18, 2026, Stainless announced it is joining Anthropic and is "winding down all hosted Stainless products, including our SDK generator." New signups, projects and SDKs closed the same day. The announcement gives no end date for existing projects.
Two things follow from that:
- Nothing you have published breaks. Stainless states that you "own the SDKs you've generated to date, and have full rights to modify and extend them however you wish."
- Regeneration has no future. Your next endpoint, renamed field or new language has nowhere to come from. The deadline that matters is your next API change, not a date from Stainless.
The hard part of leaving is not the OpenAPI document. Every generator reads that. The hard part is the public surface your users have written code against: namespaces, method names, pagination and client options. Those decisions live in stainless.yml, not in OpenAPI. Regenerate from the OpenAPI document alone and you ship a breaking change. So the most useful question to ask any alternative is: how does my existing method surface survive?
Stainless alternatives at a glance
| Tool | Documented stainless.yml import |
Generally available SDK languages | Terraform | MCP | Generator licence | Published SDK price |
|---|---|---|---|---|---|---|
| Scalar | Yes | TypeScript, Python, Go, CLI (Java, Kotlin, Ruby, C#, PHP, Rust, Swift, Dart, C++ experimental) | No (roadmap, no date) | Hosted MCP servers, Pro and above | Closed source (API reference MIT) | 1 SDK on every plan, extra SDKs $150/month each up to 100 endpoints (pricing) |
| Speakeasy | No | TypeScript, Python, Go, Java, C#, PHP, Ruby (announcement) | Yes (repo) | Generated server code | AGPL-3.0, commercial licence available | Free: 1 SDK, 50 methods (docs); Enterprise "Tailored" (pricing) |
| Fern | No | Free: TypeScript, Python; Enterprise: 10 listed, Kotlin in progress (pricing) | Not listed | Hosted docs MCP | Apache-2.0 | Free up to 200 endpoints; Enterprise custom, per SDK, billed annually |
| OpenAPI Generator | No | 89 community client generators (list) | Experimental | No | Apache-2.0 | Free |
| liblab | No | C#, TypeScript, PHP, Java, Go, Python (site) | Yes | Listed | Closed source | Not published |
| Microsoft Kiota | No | C#, Go, Java, PHP, Python stable; TypeScript, Ruby, Dart preview (repo) | No | No | MIT | Free |
| APIMatic | No | Java, Python, TypeScript, Ruby, C#, PHP, Go (site) | Not listed | MCP servers listed | Closed source | Lite $10/month (1 language, 20 endpoints); Basic $300/month per language (pricing) |
| Build in-house | Your call | Whatever you maintain | Your call | Your call | Yours | Engineering time |
"No" in the import column means we found no documented stainless.yml import on the vendor's own site. It is not a claim that migration help is unavailable. Ask each vendor directly.
The options, one by one
1. Scalar: keep your SDK surface, add docs and MCP
Verdict: the most direct path if you want your existing SDKs back under a managed generator without re-authoring anything.
Scalar's SDK generator takes your stainless.yml as an input. Resources, methods, sub-resources, models, pagination schemes and per-language package names map across. The output style is deliberately close to what Stainless users know: resource-namespaced methods, typed errors, auto-pagination, and retries that honour Retry-After. The SDK lives in your repository under your package name. Scalar opens pull requests against it and does not cut tags on your behalf. Hand-written code survives regeneration through custom code support. Scalar also reads several x-stainless-* OpenAPI extensions, so you do not need to strip them out first.
Warp is the worked example. Their SDK vendor discontinued its product, and they moved TypeScript, Python, Go and a CLI to Scalar. Every language came across at parity, with no breaking changes, and no customer needed to be told. Their CTO's summary: "A few clicks set up every language to parity with what we had." Read the Warp story.
You also get things Stainless charged for separately or did not offer: docs as a build target in the same run (so the reference and the SDK cannot drift), an MIT-licensed API reference and API client, and hosted MCP servers generated from the same OpenAPI document, with OAuth.
Where it falls short: no Terraform or SQL targets (both on the roadmap, no date). The generator is closed source. Only TypeScript, Python, Go and CLI are generally available; the other nine targets are experimental. Our MCP servers are hosted by us, not code you deploy. And Stainless's years of production traffic found edge cases that our newer generator has not yet met.
Best for: teams with TypeScript, Python or Go SDKs that must not break, who want docs and SDKs from one run at a published price.
2. Speakeasy: the like-for-like managed generator, now open source
Verdict: the strongest choice if you need Terraform providers or want to run the generator yourself.
Speakeasy has been in this category as long as Stainless. On September 17, 2026, in a partnership with Google, it open-sourced its generator as speakeasy-api/openapi-generation under AGPL-3.0. The release covers SDK generators for seven languages, a CLI generator and an MCP server generator. The repository also lists Terraform providers. Speakeasy says code generated with these tools "belongs to you in perpetuity". The README adds that the generator will not run until you elect a licence: AGPL-3.0-only, or a commercial licence token.
Where it beats Scalar: Terraform providers, a generator you can read and run, and MCP servers as code you deploy inside your own network.
Watch for: no documented stainless.yml import, so you re-express your method surface in Speakeasy's own configuration. Have legal read the licence election before you ship. Paid pricing is a sales conversation. Disclosure: Scalar and Speakeasy work together. More in Speakeasy alternatives and Scalar vs Speakeasy.
Best for: Terraform users, and teams that want the generator in their own CI.
3. Fern: docs and SDKs, with an open generator
Verdict: a strong consolidated platform, especially if your API is not only REST.
Fern was acquired by Postman in January 2026 and says the product and brand continue. Its generators are public under Apache-2.0. The free plan covers Python and TypeScript SDKs up to 200 endpoints. Enterprise lists eight more languages (Kotlin still in progress) and features such as custom code, WebSockets, gRPC and OpenRPC, priced per SDK and billed annually.
Where it beats Scalar: an open-source generator you can inspect, OpenRPC input, and a longer list of Enterprise languages than Scalar has out of experimental.
Watch for: we found no documented stainless.yml import. Much of what a Stainless user relied on sits on Enterprise. See Fern alternatives and Scalar vs Fern.
Best for: teams that want docs and SDKs together and can budget for Enterprise.
4. OpenAPI Generator: free, and nobody can wind it down
Verdict: the right answer if the lesson you took from May 2026 is "never depend on a vendor again".
OpenAPI Generator is Apache-2.0, community-maintained, and lists 80 client generators, including an experimental Terraform provider. Version 7.25.0 shipped on August 24, 2026.
Where it beats Scalar: price, language reach, and no company that can shut it down.
Watch for: Mustache-template output is rarely as idiomatic as a Stainless SDK, and it has no stainless.yml equivalent. Keeping your existing method names means owning templates and post-processing for the life of the SDK. See OpenAPI Generator alternatives and Scalar vs OpenAPI Generator.
Best for: teams with SDK engineers who want full control and zero licence cost.
5. liblab: hooks and Terraform
Verdict: worth a look if you need client-side behaviour that OpenAPI cannot describe.
liblab generates SDKs in six languages plus Terraform providers, and lists MCP support. In November 2025 it announced it is joining forces with Postman. It told existing customers that "nothing is changing for you today", and its site now offers sign-up with Postman.
Where it beats Scalar: Terraform providers, and a hooks model for injecting code into the request lifecycle.
Watch for: no published SDK price and no documented stainless.yml import. After a year in which Stainless and Fern both changed hands, ask liblab about its roadmap under Postman before you sign a multi-year deal.
Best for: teams that need Terraform plus custom request hooks.
6. Microsoft Kiota: free API clients, Microsoft-maintained
Verdict: a good free option if a plain API client is enough and your stack leans .NET or Java.
Kiota is MIT licensed. It generates API clients from OpenAPI, with C#, Go, Java, PHP and Python marked stable and TypeScript, Ruby and Dart in preview.
Where it beats Scalar: free, open source, and stable in C#, Java and PHP, where Scalar is still experimental.
Watch for: Kiota shapes the client by its own conventions and has no way to read stainless.yml, so expect your users' call sites to change. TypeScript, the most common Stainless target, is still in preview.
Best for: internal clients and .NET-heavy teams that can accept a new surface.
7. APIMatic: published pricing and long history
Verdict: a mature commercial option with a public rate card.
APIMatic generates SDKs in seven languages, plus API portals and MCP servers. Its pricing starts at $10 per month for one language and 20 endpoints, and Basic is $300 per month per language.
Where it beats Scalar: Java, C#, PHP and Ruby SDKs as part of its core offering, where Scalar's targets are still experimental, and a public price for each tier.
Watch for: per-language pricing adds up quickly, and there is no documented stainless.yml path.
Best for: teams that need several stable languages and want a price before a sales call.
8. Build in-house
Verdict: only if SDKs are your product.
The pitch is tempting: you own the code already, so hand it to a coding agent and maintain it yourself. Warp's CTO tried exactly that before moving, and "ended up with something that just seemed really brittle". His estimate for doing SDKs properly in-house was "someone working on developer products, probably 50% of their time" (Warp story).
If you do go this way, two open projects can help. stainful is MIT, runs locally and reads stainless.yml as-is, but it generates Python only as of v0.4.0. WorkOS's open-source oagen is, in WorkOS's own words, "not a turnkey generator": it parses OpenAPI and you write the emitters.
Best for: API companies with a dedicated SDK team, or Python-only APIs that want a local escape hatch.
When to stay on Stainless
Staying put is a legitimate choice for now. It is not forever.
- Your API is frozen or nearly frozen. The SDKs you generated are yours and keep working. If nothing changes, there is nothing to regenerate.
- You have an active Stainless project that still builds. Stainless has not published an end date for existing projects. Check
app.stainless.com/transitionfrom inside your account, and plan around what it says, not around hope. - You rely on a target nobody else covers the same way. If your Kotlin SDK depends on Stainless's Kotlin-first design, or you run a Terraform provider, compare the options above carefully before moving.
Whatever you decide, do two things this week. Snapshot your current api.md or public method list, so you can prove any future migration was non-breaking. And if you used the Stainless Docs Platform, fork that repository out of the stainless-sdks organisation while it is still there.
How to choose
- Must not break existing users, TypeScript, Python or Go: Scalar, because of the
stainless.ymlimport. - Need Terraform providers: Speakeasy or liblab.
- Want to run the generator yourself: Speakeasy (AGPL-3.0), Fern (Apache-2.0) or OpenAPI Generator.
- Need gRPC or OpenRPC input: Fern Enterprise.
- Want a published per-language price: APIMatic or Scalar.
- Python only, no vendor at all: stainful.
Still unsure? Scalar vs Stainless puts the two generators side by side, including where Stainless was the stronger tool.
Frequently asked questions
Is Stainless shutting down?
Stainless announced on May 18, 2026 that it is joining Anthropic and winding down all hosted products, including the SDK generator. New signups, projects and SDKs closed that day. As of September 26, 2026, Stainless had not published an end date for existing projects. See the wind-down write-up for details.
Will my Stainless-generated SDKs stop working?
No. Published packages keep working, and Stainless says you own the generated code with full rights to modify it. What stops is regeneration, so the risk arrives with your next API change.
Can I migrate without breaking my users?
Yes, if your new generator reproduces your existing method surface. Scalar does this by reading stainless.yml directly. With any tool, verify by diffing the generated api.md against your current one before you publish. The migration guide explains how.
What is the best free Stainless alternative?
OpenAPI Generator and Microsoft Kiota are free and open source, but neither keeps your existing method names without extra work. Scalar's Free plan includes one SDK for APIs up to 25 endpoints. Fern's free plan covers Python and TypeScript up to 200 endpoints. Speakeasy's free tier covers one SDK with up to 50 methods.
Which Stainless alternative generates Terraform providers?
Speakeasy and liblab both list Terraform provider generation, and OpenAPI Generator has an experimental Terraform generator. Scalar does not generate Terraform providers today.
What about the Stainless MCP server generator?
Stainless generated MCP servers as code you deploy. Speakeasy's open-source generator does the same. Scalar takes the other route: it hosts MCP servers built from your OpenAPI document, with OAuth, so there is no server for you to run. Pick based on whether the server must live inside your own infrastructure.
Related
- Learn: Generate an SDK from OpenAPI · Build vs buy an SDK
- Docs: Migrate from Stainless
- Product: SDK generator — import your
stainless.ymland regenerate without breaking your users
Researched on September 26, 2026, against Stainless's announcement and each vendor's own website, pricing page, documentation and public repositories as of that date. Vendors change pricing, licences and language support often, and Stainless's documentation may be withdrawn. We have tried to be accurate and to say where another tool is the better choice. If something here is wrong or out of date, open an issue and we will correct it, including if you work for one of the companies named above.
