In July of last year, Let's Encrypt announced that it would begin issuing Wildcard certificates for free in January of 2018. Although a little late, the organization has announced that Wildcard certificate support is now live.
In addition to these certificates, the organization has updated its ACME protocol to version 2.0. ACMEv2 is required for clients that want to use Wildcard certificates.
Wildcard certificates enable site administrators to secure all sub domains with a single certificate. This can be especially convenient for WordPress Multi-site networks.
Let's Encrypt is working on transitioning all clients and subscribers to ACMEv2, though it hasn't set a time table on when it will expire the ACMEv1 API.
In July of 2017, Let's Encrypt was securing 47 million domains. Today, the organization is securing nearly 70 million domains with 54 million certificates. In the United States, nearly 80% of sites loaded in Firefox are through HTTPS.
Let's Encrypt is an open certificate authority that's part of the non-profit Internet Security Research Group. It's mission is to make 100% of the web HTTPS. Operations are financed through sponsors and donations. If this is a mission you believe in, please consider donating to the project.