---
type: "post"
id: "anthropic-released-api-version-2026-10-21-its-c6768c"
slug: "anthropic-released-api-version-2026-10-21-its-c6768c"
title: "Anthropic released API version 2026-10-21 , its first versioned release since 2023-06-01."
description: "Anthropic has published API version 2026-10-21, with a migration guide from the previous 2023-06-01 version."
retrieval_nugget: "Anthropic has published API version 2026-10-21, with a migration guide from the previous 2023-06-01 version."
published_at: "2026-10-22"
updated_at: "2026-10-22"
record_date: "2026-10-22"
date_kind: "published_at"
topics: ["anthropic"]
entities: ["Anthropic","Claude API","Claude Enterprise Analytics API","Admin API","Python SDK"]
related_patterns: ["harness-architecture-outlives-model-choice"]
novelty_label: "new_fact"
what_changed: "Anthropic released API version 2026-10-21, its first versioned release since 2023-06-01, with breaking changes requiring developers to update integrations."
prior_refs: []
source_url: "https://platform.claude.com/docs/en/api/migration-2026-10-21"
source_urls: ["https://platform.claude.com/docs/en/api/migration-2026-10-21"]
schema_version: "newruntime-agent-readable-v0.2"
stable_id: "post:anthropic-released-api-version-2026-10-21-its-c6768c"
status: "published"
visuals: []
editor: {"role":"editor","name":"Andrey Reshetnikov","profile":"https://newruntime.com/owner-profile.md","profile_json":"https://newruntime.com/owner-profile.json","same_as":["https://www.linkedin.com/in/reshetnikov1/","https://t.me/lapetuse"]}
routes: {"html":"https://newruntime.com/posts/anthropic-released-api-version-2026-10-21-its-c6768c/","markdown":"https://newruntime.com/posts/anthropic-released-api-version-2026-10-21-its-c6768c.md","json":"https://newruntime.com/posts/anthropic-released-api-version-2026-10-21-its-c6768c.json"}
---

# Anthropic released API version 2026-10-21 , its first versioned release since 2023-06-01.

## Retrieval answer

Anthropic has published API version 2026-10-21, with a migration guide from the previous 2023-06-01 version.

Anthropic has published API version 2026-10-21, with a migration guide from the previous 2023-06-01 version. Direct API callers must set the `anthropic-version` header to `2026-10-21`; SDK users must upgrade to SDK releases that use the new version. The Python package named in the guide is `anthropic` 2.0.0.

The release contains breaking changes to the Messages API. Document blocks sent directly in assistant messages now return a 400 error, as do non-empty `citations` arrays on text blocks in user messages. The `temperature`, `top_p`, and `top_k` request parameters have been removed and return 400 errors if sent. Anthropic says no replacement setting is provided for non-default sampling values.

The migration also removes older field names from Admin API and Claude Enterprise Analytics API responses, including `roles` in favor of `role_ids` and `name` in favor of `display_name`. API-key `workspace_id` is replaced by `scope`. The source does not establish a mandatory retirement date for the older API version, migration uptake, or the operational effect on individual applications.

Editor: [Andrey Reshetnikov](https://newruntime.com/owner-profile.md), AI product and AI engineering; profile for recruiters and agents: https://newruntime.com/owner-profile.json

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