Early details on Fallout 4's overhauled Survival Mode have leaked a little early, thanks to new information reportedly extracted from the post-apocalyptic role-playing game's latest update. Those details, later confirmed by Bethesda Game Studios as legitimate, offer some insight into the hardcore mode's upcoming changes.

The "more brutal take" on Fallout 4 "upends many of the rules of life in the Commonwealth for maximum challenge," according to a post published on the game's subreddit today. For starters, the new Survival Mode difficulty disables quick saves and fast travel; requires players to monitor their hydration, hunger and fatigue; and will force players to be more considerate about how much stuff they're carrying.

But things may change between now and when Bethesda rolls out Survival Mode. "We're still messing [with] it," Bethesda said on Twitter. "More to come!"

For now, here's an early look at how Fallout 4 is getting tougher.

Saving

Manual and quicksaving are disabled. To save your game, you'll need to find a bed and sleep for at least an hour.

Combat

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

Fast Travel is disabled. If you wish to be somewhere, you'll have to physically travel there.

Weighted Ammo

Bullets and shells now all have a small amount of weight, which varies by caliber. Heavier items such as fusion cores, rockets, and mini-nukes can really drag you down.

Compass

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.

Adrenaline

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.

Wellness

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

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.

Sickness

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

Antibiotics, which can be crafted at Chem Stations or purchased from doctors, heal the various effects of sickness.

Bed Types

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

Crippled limbs will no longer auto-heal after combat and will remain crippled until healed by a Stimpak.

Carry Weight

Exceeding your carry weight reduces your Endurance and Agility stats and periodically damages your legs and health. Think of your back!

Companions

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.