The API version does not correspond to the product version. In December 2025, for example, the current WHMCS API was version 2 but the latest product version in the Release Candidate update channel was WHMCS 9.0.0.
- If we update or change the main product to resolve bugs, the product version will change but the API version may remain the same.
- If we alter either the behavior or structure of the request or response, we will increment the API version to reflect the incompatible changes.
- We may continue to support preexisting API versions for backwards compatibility. For example, we would support /api/v2/ and /api/v3/ when incrementing the version. Any calls to API v2 would continue to function normally.
- We have not yet determined our version deprecation policy.
For example, your system might run the Release Candidate update channel release of WHMCS 9.0.0 and WHMCS API v2. If you upgrade to the Stable update channel of WHMCS 9.0.0 and receive a fix for promotional code calculations, you would now run a different release of WHMCS 9.0.0 but the API version would remain the same despite that fix. This is because the change did not alter the behavior or structure of the API's requests or responses. If, however, we had added a new feature to allow multiple promotional codes, we would increment both the product tier or version and the API version.