Citing sources "close to the project," The Guardian says the encryption will be an opt-in feature because turning it on will impact some of the new machine learning features being built into the Messenger app like chat bots. Google's upcoming "Allo" messaging app also offers an opt-in end-to-end encryption option it calls "incognito mode."
Many major technology companies have taken a stronger stance on privacy, embracing end-to-end encryption following Apple's standoff with the FBI. Earlier this year, the FBI demanded Apple unlock the iPhone 5c used by San Bernardino shooter Syed Farook by bypassing Apple's own passcode security features.
Apple refused, and the FBI eventually found an alternate way to access the iPhone, but the dispute has scared technology companies into bolstering security. Dozens of major technology companies supported Apple during its fight with the FBI, all of whom were concerned about the precedent the FBI's demand could set.
Popular Facebook-owned messaging app WhatsApp enabled full end-to-end encryption in April, and in March, Swiss software developer Proton Technologies released ProtonMail, an email app offering end-to-end encryption. Apple is also rumored to be working on enhanced security measures for its software and hardware, and apps like Telegram Messenger have grown in popularity.
It is not clear exactly when Facebook might introduce new encryption options for Messenger, but the feature is said to be planned "in the coming months." Facebook declined to comment on the rumor, saying it does not respond to rumor and speculation.