API referenceSupport & configuration

Versions

Copy page



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, 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 shows how to upgrade.
  • Available on the Claude API, Claude Platform on AWS, Microsoft Foundry, and Google Cloud. On Amazon Bedrock, it's available for Claude 4.7 and later models. For other models on Bedrock, see the migration guide.
  • 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 no longer return roles. Use role_ids instead.
    • RBAC group members, and the response to removing one, no longer return group_id. Use rbac_group_id instead.
    • RBAC roles no longer return name. Use display_name instead.
    • Organization and workspace rate-limit entries no longer return group_type. Use group.type instead.
    • API keys 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 and cost reports no longer have actor.email. Use actor.email_address instead.
    • The activity summaries response no longer has summaries. Use data instead.

• 2023-06-01
  • New format for 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, rather than data-only events.
    • Removed unnecessary data: [DONE] event.
  • Removed legacy exception and truncated values in responses.
• 2023-01-01: Initial release.