Fallout 4's revamped survival mode isn't live yet, but players have already discovered how it will all work. Oh, the wonders of datamining. Detailed by Redditor rayQuGR (and confirmed by Bethesda), here are some of the harsh conditions you'll experience in Fallout 4's revamped survival mode.
Manual and quicksaving are disabled. To save your game, you'll need to find a bed and sleep for at least an hour.
Combat is more lethal for everyone. You now deal, but also take, more damage. You can increase the damage you deal even further with "Adrenaline" (see below).
Fast Travel is disabled. If you wish to be somewhere, you'll have to physically travel there.
Bullets and shells now all have a small amount of weight, which varies by calibre. Heavier items such as fusion cores, rockets, and mini-nukes can really drag you down.
Be sure to keep your eyes peeled, as enemies will no longer appear on your compass. As well, the distance at which locations of interest will appear has been significantly shortened.
Survival automatically grants the Adrenaline perk, which provides a bonus to your damage output. Unlike other perks, the only way to increase your rank of the Adrenaline perk is by getting kills (hostile or otherwise). The higher your Adrenaline rank, the higher the damage bonus. Sleeping for more than an hour, however, will cause your Adrenaline rank to lower. You can check your current Adrenaline rank at any time in the Perks section on the Stat tab in your Pip-Boy.
You'll find it difficult to survive without taking proper care of yourself. You must stay hydrated, fed, and rested to remain combat-ready. Going for extended periods of time without food, water, or sleep will begin to adversely affect your health, hurting your SPECIAL stats, adding to your Fatigue (see "Fatigue" below), lowering your immunity (see "Sickness" below), and eventually even dealing physical damage to you.
Fatigue works like radiation but affects your Action Points (AP) rather than your Hit Points (HP). The more Fatigue you've built up, the less AP you'll have for other actions. The amount of Fatigue you've accumulated is displayed in red on your AP bar.
A comprised immune system and a few questionable decisions can end up getting you killed. Eating uncooked meat, drinking unpurified water, taking damage from disease-ridden sources, such as ghouls and bugs, or using harmful Chems all put your body at increased risk for various ill effects. When you are afflicted with an illness, a message will appear onscreen. You can view specifics about your current illnesses by navigating to the Status section on your Pip-Boy's Data tab and pressing [RShoulder] to view your active effects.
Antibiotics, which can be crafted at Chem Stations or purchased from doctors, heal the various effects of sickness.
The type of bed you're sleeping in determines the length of time you are able to stay asleep. A sleeping bag will save your game and may help save your life when you're desperate, but it will never allow for a full night's rest and the benefits that come with it.
Crippled limbs will no longer auto-heal after combat and will remain crippled until healed by a Stimpak.
Exceeding your carry weight reduces your Endurance and Agility stats and periodically damages your legs and health. Think of your back!
Companions will no longer automatically get back up if downed during combat and will return home if abandoned without being healed.
Enemy and Loot Repopulation
Locations you've cleared will now repopulate enemies and loot at a significantly slower rate.
As it stands, survival mode goes beyond arbitrary difficulty challenges. It seems to consider immersion an important part of the mode. Take, for example, the Fast Travel bit. I wrote about this a while back, but the Fallout 4 experience is completely transformed when you're forced to visit every locale on foot. Walking everywhere means discovering things you'd never see or notice under normal circumstances. You're also subject to more danger, or randomised encounters. You can't just easily load/unload all your extra junk.
Having no fast travel, in addition to having to worry about food, water and fatigue, sounds kind of awesome. Tough, but worth experiencing. And that's just one part of the whole picture here. Bethesda says there's still "more to come". Awesome.