# Versioning

The current major version of the MeasureOne API is 3.0, and is passed in the API path as a `/v3` prefix.   The current 3.0 API version is `20210117` and is passed as a request header while calling the API. If no version number is specified in the request header, the API will default to the version that was live when you first signed up for MeasureOne API keys. 

We periodically release changes to our APIs. While we try to remain backward compatible, changes in our API may result in changes to the data or schema structures exposed in the current version.