Let’s Encrypt will enter Public Beta on December 3, 2015. Once we’ve entered Public Beta our systems will be open to anyone who would like to request a certificate. There will no longer be a requirement to sign up and wait for an invitation.
Our Limited Beta started on September 12, 2015. We’ve issued over 11,000 certificates since then, and this operational experience has given us confidence that our systems are ready for an open Public Beta.
Read more at Let's Encrypt blog.