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api/versioning.md

Changed on 2026-06-27 03:45:07 EST

+5 lines added
-5 lines removed
Visual Diff
# Versions¶

When making API requests, you must send an `anthropic-version` request header. For example, `anthropic-version: 2023-06-01`. If you are using the [client SDKs](/docs/en/cli-sdks-libraries/overview), this is handled for you automatically.¶

---¶

For any given version with the Messages API, 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. Previous versions are considered deprecated and may be unavailable for new users.¶

* `2023-06-01`¶
* New format for [streaming](/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.

Unified Diff

--- a/api/versioning.md
+++ b/api/versioning.md
@@ -23,9 +23,13 @@
 Anthropic recommends using the latest API version whenever possible. Previous versions are considered deprecated and may be unavailable for new users.
 
 * `2023-06-01`
-   * New format for [streaming](/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.+
+  * New format for [streaming](/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.