Survival mode

Survival mode (sometimes called Survival difficulty) is a unique gameplay mode in Fallout 4 with significant differences from 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. Survival mode can be set before starting a new game. This mode 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 are disabled. The only way to save the game is to sleep in a bed, on a mattress or in a sleeping bag. The exit save function is still available but it is a temporary save that is deleted automatically upon loading. Additionally, the use of console commands is disabled.
In case of unsolvable bugs in quests or related issues, Survival mode may be deactivated in the settings menu by choosing another difficulty to enable console commands. Even though it is stated that the deactivation of Survival Mode is irreversible, by entering the following console command , Survival Mode can be reactivated again afterwards in the settings menu.
Ammunition has non-zero weight. For example, the 10mm round has a weight of 0.025, whereas the mini nuke has a weight of 12. If the player becomes overencumbered, Agility and Endurance drop by 2, they suffer from Fatigue and take periodic damage which can cripple their legs (damage amount, limb damage amount and period/frequency are unknown). Location respawn time is 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.
While fixed enemy locations have increased repopulation times, the occurrence of random enemy encounters is two days or less.
===Summary===
GAMEPLAY 	NORMAL 	SURVIVAL
Saving 	Manual, quicksaving and autosaves are available. 	The only saves available are the exitsave (one per character) and saves made when sleeping (three per character). In some cases there is a single autosave available from just prior to exiting Vault 111. Otherwise, autosaves, quicksaves and manual saves are disabled.
Fast travel 	Fast travel is available. 	Fast travel is disabled.
Locations of interest	Easy detection of locations of interest. 	Detection of locations of interest are significantly reduced.
Location repopulation	Repopulate after 7 or 20 (for "[Cleared]") in-game days. 	Repopulate after 35 or 80 in-game days.
Stronger enemy spawns	Stronger enemies appear as the player character levels. 	Stronger enemies spawn with regularity.
Damage 	Standard damage. 	Sole Survivor does as much damage as on "Hard" Difficulty, but takes 2x more compared to it.
Experience gain 	Normal rate. 	Enemies yield 2x experience.
Available perks 	Adrenaline perk not readily available. 	Adrenaline perk is given.
Wellness 	Not subject to Exhaustion, Hunger or Thirst. 	The Sole Survivor is challenged to stay hydrated, fed and rested.
Fatigue 	Not subject to Fatigue. 	Subject to Fatigue.
Illness 	Not subject to illness. 	Antibiotics or a doctor are needed to heal illness.
Healing Radiation 	
#No negative side effects using RadAway.
#Refreshing beverage heals radiation damage up to 1,000 rads. 	
#Use of RadAway induces Fatigue and vulnerability to illness (temporary effect).
#Refreshing beverage heals radiation damage instantly, but only for 100 rads with no negative side effects.
Healing rates 	Food, stimpaks and RadAway heal instantly. 	Restorative items recover HP at a significantly reduced rate.
Crippled Limbs 	Crippled limbs auto-heal after combat. 	Crippled limbs do not auto-heal. Must be healed by a stimpak, a doctor or sleeping.
Carry Weight 	
#Ammunition is weightless.
#Not subject to ill effects of Encumbrance. 	
#Ammunition has weight. 
#Safe carry weight is significantly reduced for both the Sole Survivor and companions.
Overencumbrance 	If the Sole Survivor exceeds their carrying capacity, they will be unable to run or fast travel. Ranks 3 and 4 of Strong Back will negate these penalties.	If the Sole Survivor exceeds their carrying capacity, they will be fatigued, their Agility and Endurance will be reduced and will take periodic limb damage. Rank 4 of Strong Back will negate these new side effects.
Companions 	If knocked unconscious, companions will get back up after combat. 	If knocked unconscious, companions will not get back up after combat. They must be healed first, or they will return to their designated settlements. Non-NPC robot companions will instead be destroyed rather than returning to a settlement.
Workshop 	No limits on overall workshop inventory capacity. 	Workshop inventory capacity reduced. May affect the availability of production items (food, water, etc.).
===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 only outward teleportation point is the C.I.T. ruins. However, traveling via Vertibird using a Vertibird signal grenade is unaffected.
Alongside the changes to fast travel, the compass's range of detection has been significantly restricted to a matter of yards for locations of interest and completely removed for NPC detection, hostile or otherwise. Enemies will still show on the compass if they are quest targets, e.g. in the Taking Point or Randolph Safehouse quests.
===Combat===
In combat, there have been several key changes. Firstly, enemies have had their attack strength (damage output) and overall health/damage resistances increased. Relative to Very Hard difficulty, player outgoing damage is increased by x1.5 and player incoming damage is increased by x2.0, with both effects applied prior to any reductions for DR/ER. The Sole Survivor's damage output is increased in absolute terms but reduced relative to the greater increase in damage done by enemies. This generally results in more challenging battles (unless the enemies are given no opportunity to attack). Also, the encounter frequency of higher level enemies has been increased, adding an additional layer of difficulty.
Experience Points however, have been doubled. Additionally a new perk, Adrenaline, is automatically applied to the Sole Survivor as one rank for every five enemies they kill. This perk increases up to a 50% increase in damage, but the bonus is rapidly reduced upon sleeping, proportionate to the time slept. In addition, the healing rate of Aid items is significantly slowed, reducing the ability to offset health damage by using Aid items in mid-combat.
==Health and well-being==
In Survival mode, 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, and increasing the risk of contracting an illness. Illness risks come from various sources, such as food, drink, chem use, being hit by many creatures' unarmed attacks, immersion in water or rain. Immune deficiency can be caused by certain chems, further increasing the risk of disease. Poor sleep quality (more specifically: sleeping too frequently, for shorter periods) may increase the overall risk of disease, meaning that a pattern of using low-quality sleeping places (sleeping bags, mattresses) may indirectly increase the risk of disease (see Disease risks section below for more details). 
=== Healing ===
Additionally, sleeping in a bed for less than 7 hours will not heal all Hit Points (HP). There is a sliding scale of health recovery for sleep duration of fewer than 7 hours. Furthermore, the healing rates of all health-restorative items are significantly slowed, rather than being instant, and the use of medicinal items such as stimpaks, RadAway and chems can result in thirst, hunger and immune deficiency, which will then increase the risk of the Sole Survivor becoming ill. Healing effects from food and drinks only occur if the Sole Survivor is free from (respectively) any hunger or thirst status effects. The healing effect of drinking from water sources (contaminated or not) is greatly reduced, from 15 HP per drink to only 1.5 HP per drink, and only if there are no current thirst status effects. 
However, visiting a doctor for purposes of restoring health, removing rads,and curing addictions still carry no side effects. Paying a doctor to "Cure Health" will remove all diseases, in addition to restoring the player character to full Hit Points, at no extra charge.
Survival mode adds antibiotics, a rare loot item, craftable, also obtainable from some doctors and vendors, which will immediately cure all diseases, with no side effects. Antibiotics can be self-administered "in the field" and do not require traveling to a doctor. Survival mode also adds various herbal remedies of different types. These can be crafted, looted or bought from vendors, and are cheaper and more common than antibiotics. Each type of herbal remedy will reduce the chance of contracting certain specific disease types only (not all types). The herbal remedies are preventive rather curative: they must be taken prior to exposure, or at least, prior to sleeping (see below section on Disease risks).
===Crippling===
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, mattress or sleeping bag for two hours or by visiting a doctor for treatment. The third rank of Adamantium Skeleton however, largely negates this effect, as it makes the Sole Survivor's limbs immune to the effects of crippling.
===Companions===
The carry weight of companions has been reduced.
When downed in combat, companions will no longer heal themselves automatically and thus require a stimpak to recover from their injuries. If left unattended, they will leave the Sole Survivor's traveling party and return to their most recent settlement to recover. Codsworth will require a robot repair kit for healing if Automatron add-on is installed.
Generic robotic companions constructed at the robot workbench as part of the Automatron add-on function differently from 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. Decreases in Wellness condition are called Fatigue (not to be confused with the illness of the same name). Decreases in Wellness are communicated to the player with a "Fatigue" pop up warning. The increasing thresholds for each level of Wellness condition are on a curve. For example, it takes about 6 hours without eating to go from Well-fed to Peckish to Hungry, then a further 12 hours to go from Hungry to Famished. 
The tables in the sections below show 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 progressions can be sped up when using certain items, stimpaks and many chems inducing dehydration, RadAway causing hunger, etc.
====Effect values====
=====Hunger and Thirst=====
Generally speaking, the value that an item contributes or hinders one's wellness is equal to the monetary value of the item used (as shown in the Pip-Boy inventory, not as shown during trading with a vendor). Benefit effects tend to use the full value, while negative effects tend to use a fraction of the negative value. High monetary values (positive or negative) are capped at a maximum effect value that varies by Wellness level.
There is also a minimum effect value, generally equal to half the size of the current Wellness band (for most bands, but not all). The effect of this is that most hunger and thirst conditions can be cleared by eating or drinking two items of any type, regardless of how low their monetary value is. A consequence of this is that it is generally optimal to eat low-value food and drink to deal with hunger and thirst while saving higher-value items for their buff effects (particularly food items, whose buffs cannot be gained while hungry).
=====Disease risk=====
Unlike Hunger and Thirst, Disease uses a minimum (and maximum) base percent chance ("risk pool"), which is increased by a flat additive percent value based on the category of item or exposure event involved. This additive value ranges from +1% (normal food) to +12% for High-risk foods, with a typical value being around +5% (eg creature bites/claws) to +7% per exposure (e.g. chems and Standard-risk foods).
Only the high-risk events (which include bites, most chems, swimming and cannibalism as well as the riskier foods) also trigger an immediate, intra-day check for contracting a disease. Other exposure events (rad treatments, caffeine drinks, normal food, rain) simply accumulate risk in the disease risk pool. The disease risk pool is checked upon going to sleep, or on any high-risk event (subject to some cool-off timers). Whenever the disease risk pool is checked, it is either cleared down fully to the minimum (if a new disease is contracted) or drained slightly (if no new disease is contracted).
Disease risk is directly increased by overall Fatigue (the inverse of Wellness). Fatigue is a weighted average of Hunger, Thirst and Sleep factors. Hence it is important to minimize all these aggravating risk factors, particularly prior to sleeping.
Taking herbal remedies will reduce the disease chance by -20%, for the diseases that the specific remedy protects against. However, the remedy must be taken no more than one game hour prior to the risk check (sleeping or high-risk event). 
If the player character is in an immune-suppressed state (a side effect of RadAway and the mysterious serum), then the total disease risk is increased x 120%. (It may be advisable not to sleep until this effect state has expired.)
Any amount of sleeping will clear down the disease risk pool to its minimum value, adjusted for Wellness. Low quality sleep (on mattresses, etc.) may increase the overall chance of getting a disease, if the effects of Fatigue outweigh the effects of reducing the risk pool to the minimum level, particularly considering that more frequent sleep will lead to more frequent disease checks.
Generally, the best time to take disease prevention measures is just before sleep or (if it can be anticipated) just before high-risk exposure. It is a very good idea to be fully fed and fully hydrated at the point of going to sleep, particularly if the player character is also tired and/or has had high exposure to disease risk factors.
=====Disease risk values=====
Foodstuffs with Standard disease risk in raw form (+7% to risk pool):	Foodstuffs with High disease risk in raw form (+12% to risk pool):	All other foodstuffs presumably have the +1% default risk. Including:
* Dirty water - bottled, raw or (via mods) pumped
* Bloatfly meat (safer than most other insects)
* Blood packs
* Brahmin meat
* Cat meat
* Cave fungus
* Pretty much all raw meat/eggs not listed in the right columns	
* Mutant hound meat
* Glowing blood pack
* Moldy food
* Lukowski's potted meat
* Glowing one meat
* Ghoul meat (from a specific quest)
* Bloodbug meat
* Stingwing meat
* Radroach meat
* Molerat meat	
* All prepared or cooked foods not listed in the left columns
* All raw crops and wild plants
* Pristine deathclaw egg
* Brain fungus
* Glowing fungus
* Canned dogfood
*Special cases
** +0% to pool for Purified Water, no check
**+2% to pool for Nuka-Cola, no check
Chems trigger +7% to the risk pool, immediate check. (From a script comment it looks like all addictive Chems will trigger this.)
====Hunger====
While the Sole Survivor is hungry (including Peckish, anything other than Well Fed), the healing and bonus properties of normal (non-wild) food consumption is suppressed until enough is consumed to make the survivor Well Fed.
Eating normal food that grants a bonus (e.g. the +1 Agility of deathclaw steak) while not Well Fed will remove the bonus if it is already active. For example, eating a deathclaw steak while not hungry to gain the bonus, then becoming Peckish, then eating a second deathclaw steak to become well-fed will negate the +1 Agility bonus and would require eating a third deathclaw steak to regain it. This is probably a bug.
The amount of food that must be eaten to reduce hunger is relative to its quality (which is equal to its nominal 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, to the same value as their nominal price, so in effect have double worth or double effect.
Wild plants in general do not reduce hunger, but they do apply their other buffs regardless of whether the player is Well Fed or not. Razorgrain also behaves this way, which is almost certainly a bug. Certain wild plants (wild corn, wild mutfruit, wild tarberry, silt bean) behave like normal plants, not wild plants, in this regard.
The Cannibal perk has a special interaction called Dark Craving when eating a corpse is used to satisfy hunger.
====Thirst====
Thirst will negatively impact the Intelligence, Luck and Perception stats, until corrected. Drinking dirty water, either bottled or directly from open water sources such as puddles and rivers, increases the possibility of contracting an illness. 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, or directly (without needing to supply an empty bottle) from the workshop inventory of a settlement with a water supply surplus, as in a vanilla game.
Typically the player character will require around 9 drinkable items per game day to remain fully hydrated, two items per 4 game hour period when awake, and one more item per 8 game hours of sleeping. 
Nuka-Cola (and variants) give only 40% of the expected thirst reduction, based on their monetary value (capped), and cause increased hunger equal to 20% of their monetary value (capped).
====Sleep====
Sleeping for at least one game hour on any bed, mattress, or sleeping bag will save the game, but have no other effect other than causing a disease check. Sleeping longer (two hours or more) will heal crippled limbs, progressively heal Hit Points, and begin to reduce Fatigue levels that the player character has developed from being tired (but not Fatigue from hunger or thirst). Healing of Hit Points can proceed over multiple sleeping sessions. Each sleeping session causes one disease check of the current disease risk pool.
It is possible to sleep for zero hours by hitting Cancel immediately after hitting the sleep command. This saves the game and carries out all of the normal disease checks, but does not reduce tiredness or grant any healing.
The Sole Survivor cannot sleep more than 3 game hours in a sleeping bag or tent, and more than 5 hours on a mattress. A mattress cannot reduce the sleep Fatigue state below "Tired" and a sleeping bag cannot reduce any existing sleep Fatigue state of "Weary" or less (Tired, Overtired or Weary). Sleeping on a mattress or sleeping bag can prevent entering these sleep Fatigue states, but cannot remove them once they have been acquired. If no better place to sleep is available it becomes important to anticipate when the next worst sleep state will arrive, and sleep before that happens.
To sleep for longer amounts of time, or to fully remove all sleep Fatigue states, 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. 
More frequent sleeping indirectly increases the risk of contracting a disease, particularly if there is exposure to disease risk events between sleep. This is because while sleeping clears down the accumulated increased disease risk, a higher minimum risk is imposed by Fatigue (including hunger and thirst), and a disease check is forced each time the player goes to sleep, checked prior to any reduction in the disease risk pool.
Sleeping for 7 game hours or more allows one to recover full health and if sleeping in a bed as opposed to a mattress or sleeping bag, will ensure one is well rested and minimizes the risk of illness. Being asleep for any period of time, in any bed, of any type, will force a check for illness. It will then clear the disease risk pool down to the Fatigue-adjusted minimum (see the Disease risk section) regardless of how brief the period of sleep is.
=====Sleep timer=====
The sleep timer or sleep counter runs for 14 game hours after waking up fully rested. 
The message "You feel rested" appears after sleeping, when the sleep timer has been fully cleared. If the player is not currently at the Tired state or worse, 2 hours of sleep is sufficient to clear this timer completely and permit up 14 hours before becoming Tired. Sleeping for only 1 hour risks the player character entering the Tired state after waking up.
=====Minimum sleep requirements=====
The absolute minimum sustainable amount of sleep while avoiding the Tired state is to sleep 2 hours in a bed after every 13–14 hours (39-42 real-time minutes) of being awake (theoretically 14 hours but only given perfect timekeeping and no combat). This would mean sleeping 4 out of every 26-32 hours.
With only a single regular sleep time each day, the optimum sleep duration would be 10 game hours asleep then 14 hours awake (if there is no combat, see below); otherwise, the player character will get the Tired warning at a different time on each successive day.
=====Entering combat=====
Entering combat (not including just sprinting) increments the sleep counter by 15 game minutes, i.e. brings the next sleep Fatigue condition 15 minutes closer. (There is a cooldown timer on this counter, so entering combat 56 times in immediate succession will not cause an increase in sleep fatigue state.)
=====Day 1 anomalies=====
On the first day of the game, upon leaving the Vault (always) at 9am, the player will become Tired at 11am unless they sleep prior to that time (or sooner if they enter combat). However if sleeping prior to becoming Tired on the first day (only), the sleep timer is fully reset (even if sleeping for zero hours), granting the full normal 14 hours before the player becomes Tired. (This benefit may not persist if restoring from a saved game that was saved at that point.)
=====Caffeine and alcohol=====
Consuming caffeinated drinks such as Nuka-Cola will delay the need to sleep for some time. They also will temporarily reduce the current tiredness state by (usually) one step. However, caffeinated drinks have hunger increasing effects as well as reduced thirst-quenching effects. Alcoholic drinks will typically cause increased Thirst rather than reducing it.
====Waiting====
Unlike sleeping, waiting (using an item of furniture) does not reduce the rate of hunger increase or thirst increase, does not heal damage, and does not clear or reduce the disease risk pool. Hunger, thirst and tiredness all continue to accumulate normally while waiting.
However waiting does not trigger a disease pool check like sleeping does. Also, periodic damage effects, caused by extreme states of hunger or thirst, overencumbrance or the "Infection" disease, will not occur while waiting.
As in normal mode, waiting will (like sleeping) completely avoid the effects of rad storms, avoiding the need to seek shelter inside an interior cell.
====Disease types====
There is no correlation between player character actions and any particular disease type. Disease type is almost totally random, the only exception being that the game will not assign the same disease type consecutively. (But might well assign first one disease, then a different one, then the first one again).
It is not possible to contract more than one disease per game day, and it is not possible to contract a disease on the first game day. Subject to this, it is possible to have multiple diseases at the same time, and it is theoretically possible to contract all disease types simultaneously.
==Notes==
The game's daily requirement of water to maintain full hydration, 9 units x 0.5 lbs = 4.5 lbs, is lower than the generally stated human daily requirement for water which is usually put at around 8 lbs or 3.7 liters for adult males, 6 lbs or 2.7 liters for adult females (though 20% of that total includes water present in food).
==Bugs==
* If the squirrel stew is used to satisfy both the Parched and Peckish effects simultaneously while another food bonus is already in effect, this food bonus will become permanent. The bonus description will disappear from the Status menu the moment the squirrel stew is eaten but the bonus itself will remain and can be checked in the SPECIAL page or in the affected stat section if such bonus involves Damage Resistance, Energy Resistance or others. Some bonuses cannot be checked without console commands, so if one wishes to avoid accidentally exploiting this glitch, it's best not to use the squirrel stew while another food bonus is in effect.
* 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.
* Cleansing the Commonwealth for Knight Rhys seems to have a bug when getting the Clear Breakheart Banks quest. No flag appears on the super mutants, and no objective is given for finishing the quest. Since the use of the console isn't allowed, no fix is available.
* Due to the increased respawn times, Cleansing the Commonwealth and similar quests may run out of targets to send the player to.
* As noted above in the Hunger section, Razorgrain behaves like a wild plant for nourishment purposes, and three wild plants behave like their domesticated equivalents. 
==See also==
* Fallout: New Vegas Hardcore mode
* Fallout Shelter Survival mode
Category:Fallout 4 gameplay
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