Survival (Fallout 4)

Survival mode is a unique gameplay mode in Fallout 4 with significant differences to other modes. Survival mode was added to the game for all platforms on March 29, 2016. It replaced the existing Survival difficulty, which was renamed to Very Hard.

General features
Survival mode can be accessed in the options menu. Unlike Hardcore mode used in Fallout: New Vegas, Survival mode can be set before starting a new game. This mode also cannot be toggled freely. Once Survival mode is activated, turning it off will permanently disable it from being reactivated for that save file.

In survival mode, autosave and manually saving from the menu has been disabled. The only means of physically saving the game is to sleep in a bed, on a mattress, or in a sleeping bag. The exit save function is still available, but is a temporary save that is deleted automatically upon loading. Additionally, the use of console commands is disabled.

Ammunition now has a set weight, per rounds, based on the ammunition type. For example the 10mm round has a weight of 0.025 per round, where as the mini nuke has a weight of 12. If one becomes over-encumbered, their Agility and Endurance will drop by 2, they will suffer from Fatigue and they will take constant damage to their legs. Rather than permitting fast travel while over-encumbered, the perk Strong Back eliminates these negative effects. Further to this, carry weight for the Sole Survivor and their companions has also been reduced.

Locations take 35 in-game days for non-cleared locations and 80 in-game days for cleared locations to repopulate enemies and loot, as opposed to the standard 7 and 20 days respectively. Additionally, the workshop's inventory has been restricted, which it may affect the availability of production items. 

Travel and navigation
Fast travel is disabled, with the exception of entering the institute, which can only be entered via fast travel while they are an available faction. Being a member of the Institute however, will not allow one to bypass fast travel's elimination as the out outward teleportation point is the C.I.T. ruins.

Alongside the changes to fast travel, the compass's range of detection has been significantly restricted to a manner of meters for locations of interest and completely removed for NPC detection, hostile or otherwise.

Combat
In combat, there have been several key changes. Firstly enemies have had their attack strength and overall health/damage resistances increased, resulting in more challenging battles. Also the encounter frequency of higher level enemies has been increased, adding an additional layer of difficulty.

Experience Points however, have been doubled. Additionally new perk, Adrenaline, is automatically applied to the Sole Survivor for every two enemies they kill. This perk gradually increases up to a 50% increase in damage.

Health and well-being
Prior to survival, only Fallout: New Vegas '  hardcore mode made food and drink a necessity. The Sole Survivor must remain hydrated, eat periodically and have a regular sleep cycle in order to survive. Failure to manage one's well being will result in negative effects such as Fatigue, Hunger and Thirst. reducing maximum AP. Additionally one can contract an illness from various sources, such as over sleeping on a matress or from use if medicinal items.

Additionally sleeping in a bed for less than 7 hours no longer heals Hit Points (HP). Furthermore, the healing rates of restorative items are significantly slowed and the use of medicinal items such as Stimpaks, RadAway, and chems can result in thirst and in some instance cause the Sole Survivor to become ill.

If one is crippled in any form, this no longer recovers with time and must be rectified with a stimpak, by sleeping in a bed until the Sole Survivor is well rested or by visiting a doctor. The third rank of Adamantium Skeleton however, largely negates this effect, as it makes the Sole Survivor's limbs immune from the effects of crippling.

When downed in combat, companions will no longer heal themselves automatically, thus requiring a stimpak to be brought back. If left unattended, they will leave the Sole Survivor's travelling party and return to their most recent settlement to recover. Generic robotic companions constructed in the robot workbench as part of the Automatron add-on function differently to other companions. As they no longer hold essential status, they will explode on death, becoming unrecoverable.

Wellness
There are five stages in each category of wellness that span in-game hours. The increasing thresholds for each form of wellness are on a curve, for example, it takes about 6 hours to go from well-fed to peckish to hungry, then a further 12 hours to go from hungry to famished. The following table shows the approximate times that it takes for a character to go from completely satisfied to the listed condition in each area. In-game time is expressed in "hours" and real-time is expressed in "minutes." These effects can be sped up when using certain items. Stimpaks and other drugs inducing dehydration, RadAway causing hunger, etc.

Thirst
Thirst will negatively impact the Intelligence, Luck and Perception stats, making it more likely one will drink directly from manual water pumps, water fountains and open water sources such as puddles and rivers. Drinking from irradiated sources has the possibility of afflicting one with an illnesses. As a means of ensuring one has a steady supply of water, the Sole Survivor can now fill empty bottles with dirty or purified water. Dirty water is obtained from sources such as rivers, puddles or ponds. Purified water is obtained from water pumps and water fountains.

Hunger
While the Sole Survivor is hungry, the healing and bonus properties of food consumption is suppressed until enough is consumed to make the survivor "well-fed." However, eating something that grants a bonus while hungry will remove the bonus if it is already active. For example, eating a deathclaw steak while not hungry to gain the bonus of +1 agility, then becoming Peckish, then eating a second deathclaw steak to become well-fed will negate the bonus received and would require eating a third deathclaw steak to regain it.

The amount of food that must be eaten to do this is relative to its quality (or price), i.e, a ribeye steak satisfies hunger more than a grilled radroach. Certain foods, such as soups and certain crops, will satisfy both hunger and thirst.

Sleep
Sleeping for at least one hour on any bed, mattress or sleeping bag will save the game, and remove any Fatigue the player character has developed from being tired. The Sole Survivor cannot sleep more than 3 hours in a sleeping bag and more than 5 hours on a mattress. To sleep for longer amounts of time, it is required to use a real bed. Attempting to sleep for longer than these times will result in one waking up at the time threshold and any further attempt to sleep may result in an illness (e.g. parasites.)

Sleeping for seven hours or more allows one to recover health and if sleeping in a bed as opposed to a mattress or sleeping bag, will ensure one is well rested and minimizes risk of illness. Being only asleep for one hour in any bed, even at a workshop settlement, will still grant a high risk for illness, in particular parasites. Lethargy, insomnia and weakness are common.

Note: The in-game / real-time data in the tables above are approximations only.

Bugs

 * Starting in Survival mode and later changing the game mode will not change the water production from Water Purifiers.
 * When first joining the Railroad after completing Tradecraft, the message "You can now fast travel to and from Railroad HQ" still appears, despite the fact that fast travel is disabled in Survival mode.