---
title: Versions
url: https://platform.claude.com/docs/en/api/versioning
description: "When making API requests, you must send an `anthropic-version` request header. For example, `anthropic-version: 2026-10-21`. If you are using the [client SDKs](https://platform.claude.com/docs/en/cli-sdks-libraries/overview), this is handled for you automatically."
---

For any given API version, Anthropic preserves:

* Existing input parameters
* Existing output parameters

However, Anthropic may do the following:

* Add additional optional inputs
* Add additional values to the output
* Change conditions for specific error types
* Add new variants to enum-like output values (for example, streaming event types)

Generally, if you are using the API as documented in this reference, Anthropic will not break your usage.

## Version history

Anthropic recommends using the latest API version whenever possible.

* `2026-10-21`

  * [Migrating to API version 2026-10-21](https://platform.claude.com/docs/en/api/migration-2026-10-21) shows how to upgrade.

  * Available on the Claude API, [Claude Platform on AWS](https://platform.claude.com/docs/en/build-with-claude/claude-platform-on-aws), [Claude Models on Google Cloud (Anthropic managed)](https://platform.claude.com/docs/en/build-with-claude/claude-models-on-google-cloud/anthropic-managed), [Microsoft Foundry](https://platform.claude.com/docs/en/build-with-claude/claude-in-microsoft-foundry), and [Claude Models on Google Cloud (Google managed)](https://platform.claude.com/docs/en/build-with-claude/claude-models-on-google-cloud/google-managed). On [Amazon Bedrock](https://platform.claude.com/docs/en/build-with-claude/claude-in-amazon-bedrock), it’s available for Claude 4.7 and later models. For other models on Bedrock, see the [migration guide for API version 2026-10-21](https://platform.claude.com/docs/en/api/migration-2026-10-21#upgrade).

  * Messages API:

    * A request that places a `document` block directly in an `assistant` message returns a 400 error.
    * Sending a `text` block with a non-empty `citations` array in a `user` message, directly or inside a `search_result` block, returns a 400 error.
    * The `temperature`, `top_p`, and `top_k` request parameters are removed. A request that sends any of them returns a 400 error on every model.

  * Admin API:

    * [RBAC groups](https://platform.claude.com/docs/en/api/beta/organization/rbac_groups/list) no longer return `roles`. Use `role_ids` instead.
    * [RBAC group members](https://platform.claude.com/docs/en/api/beta/organization/rbac_groups/members/list), and the response to removing one, no longer return `group_id`. Use `rbac_group_id` instead.
    * [RBAC roles](https://platform.claude.com/docs/en/api/beta/organization/rbac_roles/list) no longer return `name`. Use `display_name` instead.
    * [Organization](https://platform.claude.com/docs/en/api/organization/rate_limits/list) and [workspace](https://platform.claude.com/docs/en/api/organization/workspaces/rate_limits/list) rate-limit entries, and the response to [setting a workspace’s rate limits](https://platform.claude.com/docs/en/api/organization/workspaces/rate_limits/update), no longer return `group_type`. Use `group.type` instead.
    * [API keys](https://platform.claude.com/docs/en/api/organization/api_keys/list) no longer return `workspace_id`. Use `scope.workspace_id` instead, which gives the workspace’s real ID even for the Default Workspace (an all-workspaces key has no `workspace_id` in `scope`).

  * Claude Enterprise Analytics API:

    * The per-user [usage](https://platform.claude.com/docs/en/api/beta/organization/analytics/user_usage_report/list) and [cost](https://platform.claude.com/docs/en/api/beta/organization/analytics/user_cost_report/list) reports no longer have `actor.email`. Use `actor.email_address` instead.
    * The [activity summaries](https://platform.claude.com/docs/en/api/beta/organization/analytics/summaries/list) response no longer has `summaries`. Use `data` instead.

* `2023-06-01`

  * New format for [streaming](https://platform.claude.com/docs/en/build-with-claude/streaming) server-sent events (SSE):

    * Completions are incremental. For example, `" Hello"`, `" my"`, `" name"`, `" is"`, `" Claude." `instead of `" Hello"`, `" Hello my"`, `" Hello my name"`, `" Hello my name is"`, `" Hello my name is Claude."`.
    * All events are [named events](https://developer.mozilla.org/en-US/Web/API/Server-sent%5Fevents/Using%5Fserver-sent%5Fevents#named%5Fevents), rather than [data-only events](https://developer.mozilla.org/en-US/Web/API/Server-sent%5Fevents/Using%5Fserver-sent%5Fevents#data-only%5Fmessages).
    * Removed unnecessary `data: [DONE]` event.

  * Removed legacy `exception` and `truncated` values in responses.

* `2023-01-01`: Initial release.