Microsoft is rolling out to Skype Insider testers a preview of the coming end-to-end encrypted private conversation feature.

In a short blog post on January 11, Microsoft officials noted that the coming end-to-end encryption will work for audio calls, text messaging and image, audio and video file transmission.

Microsoft has been touting Skype as being encrypted for some time, noting it uses 256-bit AES encryption. But this isn’t the same as end-to-end encryption. End-to-end encryption means not just the communication channel is secure but the messages stored on servers can only be read by those involved in the communications.

Microsoft competitors including Apple with iMessage, WhatsApp and Signal already provide built-in end-to-end encryption.

Skype’s end-to-end encryption will use the industry standard Signal Protocol from Open Whisper Systems.

During the preview, users only will be able to start private conversations with other Skype Insiders using the latest preview version, and interactions will be limited to one-to-one conversations.

Microsoft says it plans to work on improving the user experience around invitations to join private conversations , and to bring this to the Universal Windows Platform Skype client. For now, Private Conversations with end-to-end encryption is available only to Skype Insider testers using Skype 8.13.76.8 for iOS, Android, Linux, Mac and Windows Desktop.

There’s no word as to when Microsoft expects to roll out end-to-end encryption to all Skype users.