Send API v3.1 has been released in August 2017 bringing new functionalities, better error reporting and top-notch developer experience. Mailjet is still supporting Send API V3.
If you are a current user of Send API in version 3, we listed the changes you will need to take into account to migrate to v3.1.
Read this blogpost to learn more on how we designed our Send API V3.1 and where our Transactional Suite is going to.