Lets Encrypt has reached a point where we’re ready to announce our launch schedule. We will issue the first end entity certificates under our root under tightly controlled circumstances. No cross-signature will be in place yet, so the certificates will not validate unless our root is installed in client software. As we approach general availability we will issue more and more certificates, but only for a pre-approved set of domains. This limited issuance period will give us time to further ensure that our systems are secure, compliant, and scalable.”]
Source: https://letsencrypt.org//2015/06/16/lets-encrypt-launch-schedule.html