# Versions¶
¶
When making API requests, you must send an `anthropic-version` request header. For example, `anthropic-version: 2023-06-01`. If you are using our [client SDKs](/docs/en/api/client-sdks), this is handled for you automatically.¶
¶
---¶
¶
For any given API version with the Messages API, we will preserve:¶
¶
* Existing input parameters¶
* Existing output parameters¶
¶
However, we 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, we will not break your usage.¶
¶
## Version history¶
¶
We always recommend 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.