To elaborate on this, a CTA would directly transfer the contribution of the copyright to the project. A CLA is much more common than a CTA. A CLA is more compli

To elaborate on this, a CTA would directly transfer the contribution of the copyright to the project. A CLA is much more common than a CTA. A CLA is more complicated: the submitter maintains the copyright, but a sublicense is granted to the project. That sublicense grants rights similar to having copyright, one of them being the ability to relicense. It is possible for the CLA sublicensing agreement to restrict the ability to relicense, but most do not do that.