First new version since 2023
Anthropic on Oct. 21 (Oct. 22 Japan time) released a new version, "2026-10-21," of its Claude API for developers. API versions are a system of marking major specification changes by date, and the new version is the first since "2023-06-01" in June 2023. @ClaudeDevs, the company's X account for developers, made the announcement.
The version used is selected with a header attached to the request. The new SDK versions send 2026-10-21 by default. The old 2023-06-01 version has not been deprecated, and no end date has been given. Users who keep using the old SDKs will continue to run on 2023-06-01 as before.
Settings for output randomness dropped
The main change in the new version is that the API for generating text (the Messages API) no longer accepts "temperature," "top_p" or "top_k," which control the randomness of output. Sending them returns an error even if the values are the same as the defaults. If they are removed, the API runs with the defaults (1.0 for temperature). The company advises that processes that truly need non-default values stay on the old version.
The company's recent models already accepted these settings only at their defaults, so behavior does not change with those models. The migration guide does not explain why the settings were dropped.
In addition, sending a document as Claude's reply and attaching citation information to the text of a user's message will also return errors. In the administrative API, the names of some fields have changed.
Major SDK updates in 7 languages
New major versions of the SDKs were released in 7 languages. They include 2.0.0 for Python, 1.0.0 for TypeScript, 2.0.0 for Go and 3.0.0 for Java, and the command-line tool "ant" was also moved to 2.0.0.
| Language | New version |
|---|---|
| Python | 2.0.0 |
| TypeScript | 1.0.0 |
| Go | 2.0.0 |
| Java | 3.0.0 |
| C# | 13.0.0 |
| Ruby | 2.0.0 |
| PHP | 1.0.0 |
| ant (command line) | 2.0.0 |
Change in how keys are sent
The SDKs changed how API keys are sent to the "Authorization: Bearer" format. The API itself accepts both formats, but proxies that relay traffic or logging settings that assume the old format will need to be fixed. The option to write a key directly on the command line was removed. Starting with the new versions, the license changes from the MIT license to Apache 2.0. On Amazon's Amazon Bedrock, the new version can be used only with Claude 4.7 and later models.
