Bethesda earlier today, tweeted that beta testing on the overhauled Survival Mode will begin soon on Steam. For all the die hard survivors of the wasteland comes a new mode to play Fallout 4 in. In this mode, weapons are more lethal, you will have to be careful where you sleep as some places will give you better rest than others. Saving is now more difficult, so if you like the ability to save whenever you want this is not the mode for you. In order to save you would need to sleep somewhere for at least an hour. You would have to physically travel from place to place rather than by simply clicking somewhere to magically transport there.
This new game mode adds in a more realistic game play of the harsh apocalyptic world. You will have to take care of yourself meaning staying hydrated, resting, taking care of companions, repopulation of hostile territories, limbs will remain crippled until healed, the compass will not point out enemies, and taking care of your health from illness. More in detail analysis of this mode can be found in this article.
With this mode entering beta phase, the exact details of the mode are subject to be changed when the mode is released. The official release date of the mode has not been given yet.