---
title: "Anthropic SDK and CLI versions include breaking changes: 2026-10-21 | Harbyn"
description: "Anthropic SDK and CLI versions include breaking changes, announced Oct 21, 2026."
canonical: "https://harbyn.com/changes/anthropic/2026-10-21-sdk-and-cli-versions-include-breaking-changes"
last-updated: 2026-10-25
---

# Anthropic SDK and CLI versions include breaking changes

Markdown version of <https://harbyn.com/changes/anthropic/2026-10-21-sdk-and-cli-versions-include-breaking-changes>.

Breaking change - Anthropic. medium severity. In effect.

The October 21 SDK and ant CLI releases include breaking changes independent of API version and switch from MIT to Apache 2.0 licensing. They also send API version 2026-10-21 by default. Review the vendor migration guide before upgrading.

## Facts

| Fact | Value |
| --- | --- |
| Vendor | [Anthropic](https://harbyn.com/vendors/anthropic.md) |
| Kind | Breaking change |
| Severity | medium |
| Status | In effect |
| Announced | Oct 21, 2026 |
| Added to Harbyn | Oct 25, 2026 |
| Lead time | No dated deadline |
| Review | Reviewed by a person, extracted by a model |

## Find it in your code

```sh
npx harbyn scan
```

This change names no identifier the scanner can match line by line, so the scan tells you whether your repository uses Anthropic, from its packages and API hosts. Nothing leaves your machine.

## Sources

Where this event comes from: the page we read, when we read it, and the hash of that snapshot.

- <https://platform.claude.com/docs/en/release-notes/overview.md> (changelog, fetched 2026-10-22 03:34 UTC, sha256 `632020f4b3f31e65f9e9aa4b3a0a32d19a9bed30be6104247f0251f8753aafde`)

## Related changes

### More from Anthropic

- [Claude Haiku 5.5 rejects manual extended thinking and returns thinking blocks by default](https://harbyn.com/changes/anthropic/2026-10-07-claude-haiku-5-5-behavior-can-break-code-written-for-claude-haiku-4-5.md) (Behavior change, announced Oct 7, 2026)
- [Limited networking applies allowed\_hosts to web tools](https://harbyn.com/changes/anthropic/2026-10-07-limited-networking-applies-allowed-hosts-to-web-tools.md) (Behavior change, announced Oct 7, 2026)
- [Claude Sonnet 4.5 model: retirement on 2026-11-30](https://harbyn.com/changes/anthropic/2026-09-30-claude-sonnet-4-5-model-retirement.md) (Retirement, effective Nov 30, 2026)
- [Claude Sonnet 5.5 rejects five Claude Sonnet 5 request patterns](https://harbyn.com/changes/anthropic/2026-09-28-claude-sonnet-5-5-changes-compatibility-with-claude-sonnet-5-code.md) (Behavior change, announced Sep 28, 2026)

### Changes at other vendors

- [Amazon Selling Partner API: October listing attribute usage and enumeration value updates](https://harbyn.com/changes/amazon-sp-api/2026-10-14-sp-api-updates-new-listings-items-api-ivp-values-in-eu5-jp-and-ca-stores-oct-2.md) (effective Oct 26, 2026)
- [Supabase: four CBC-mode TLS 1.2 cipher suites will be removed from project HTTP APIs](https://harbyn.com/changes/supabase/2026-10-12-an-outdated-subset-of-tls-1-2-ciphers-will-be-disabled-on-project-http-apis.md) (effective Nov 10, 2026)
- [Google Workspace APIs: OAuth clients must be marked as agentic to call Google Workspace MCP servers](https://harbyn.com/changes/google-workspace/2026-10-12-oauth-clients-must-be-marked-as-agentic-to-call-google-workspace-mcp-servers.md) (effective Nov 11, 2026)
- [Bitbucket Cloud API: Git Credential Manager upgrade required for OAuth 2.0 Git authentication](https://harbyn.com/changes/bitbucket/2026-10-13-git-credential-manager-upgrade-required-for-oauth-2-0-git-authentication.md) (effective Nov 30, 2026)

[All upcoming deadlines](https://harbyn.com/deadlines.md)