12  Appendix D: Game File Structure

This appendix provides a complete reference of BL4’s file structure, asset organization, and content layout.

12.1 Overview

Property Value
Engine Unreal Engine 5.5
Asset Format IoStore (.utoc/.ucas) with Zen packages
Total Assets ~119,299 files in pak archives
Extracted to Manifest 81,097 assets
Internal Codename Oak2
Max Players 4

12.2 File Locations

12.2.1 Steam (Linux)

~/.steam/steam/steamapps/common/Borderlands 4/OakGame/Content/Paks/

12.2.2 Steam (Windows)

C:\Program Files (x86)\Steam\steamapps\common\Borderlands 4\OakGame\Content\Paks\

12.3 Pak Chunk Contents

Chunk Contents
pakchunk0-Windows_0_P Core game assets, weapons, gear
pakchunk2-Windows_0_P Audio (Wwise .bnk)
pakchunk3-Windows_0_P Localized audio
pakchunk10-Windows_0_P Large assets

12.4 Top-Level Content Structure

OakGame/Content/
├── AI/                     # Enemy AI, NPCs, bosses
├── Atlases/                # Texture atlases
├── Cinematics/             # Cutscene assets
├── Common/                 # Shared materials/resources
├── Dialog/                 # Dialogue assets
├── Editor/                 # Editor-only assets
├── Fonts/                  # Font assets
├── GameData/               # Core game configuration
├── Gear/                   # All equipment
├── GeometryCollections/    # Physics destruction meshes
├── Gore/                   # Gore effects
├── Grapple/                # Grappling hook system
├── InteractiveObjects/     # World interactables
├── LevelArt/               # Level-specific art
├── LevelLighting/          # Lighting setups
├── Maps/                   # Game maps/levels
├── Missions/               # Mission data
├── Pickups/                # Item pickup visuals
├── PlayerCharacters/       # Vault Hunters
├── UI/                     # UI assets
├── uiresources/            # UI resource files
├── WeatherOcclusionBakedData/
└── World/                  # World building assets

12.5 Player Characters (Vault Hunters)

PlayerCharacters/
├── Customizations/         # Player cosmetics
├── DarkSiren/              # Character: Dark Siren
├── ExoSoldier/             # Character: Exo Soldier
├── Gravitar/               # Character: Gravitar
├── Paladin/                # Character: Paladin
├── _Shared/                # Shared character resources
└── Temporary/              # Development/testing

12.6 Gear System

12.6.1 Equipment Types

Gear/
├── ArmorShard/             # Armor shard items
├── Enhancements/           # Enhancement items
├── Firmware/               # Firmware upgrades
├── Gadgets/                # Deployable gadgets
│   ├── HeavyWeapons/       # Heavy weapon gadgets
│   ├── Terminals/          # Terminal gadgets
│   └── Turrets/            # Turret gadgets
├── GrenadeGadgets/         # Grenades
│   ├── Manufacturer/
│   │   └── VLA/            # Vladof grenades
│   └── _Shared/
├── RepairKits/             # Repair kit items
├── ShieldBooster/          # Shield boosters
├── shields/                # Shields
│   ├── BalanceData/
│   ├── Manufacturer/
│   │   └── VLA/            # Vladof shields
│   └── _Shared/
├── Vehicles/               # Vehicle equipment
│   └── HoverDrives/        # Hover drive upgrades
├── Weapons/                # Guns
└── _Shared/                # Shared gear resources
    ├── BalanceData/
    │   ├── Anoints/        # Anointment system
    │   ├── Economy/        # Currency/cost data
    │   └── Rarity/         # Rarity definitions

12.6.2 Weapon System

Gear/Weapons/
├── _Manufacturer/          # Manufacturer-specific data
│   ├── BOR/                # Borg
│   ├── JAK/                # Jakobs
│   └── TED/                # Tediore
├── Pistols/                # Pistol weapons
├── Shotguns/               # Shotgun weapons
├── SMG/                    # SMG weapons
├── Sniper/                 # Sniper weapons
└── _Shared/
    └── BalanceData/
        ├── BarrelData/         # Barrel parts
        ├── _BaseWeaponData/    # Base weapon stats
        ├── BorgChargeData/     # Borg charge mechanics
        ├── COV/                # COV overheat/repair
        ├── Elemental/          # Elemental damage types
        ├── MagazineData/       # Magazine parts
        ├── Order/              # Order faction weapons
        ├── Rarity/             # Weapon rarity modifiers
        ├── ScopeData/          # Scope parts
        ├── TED/                # Tediore-specific data
        ├── UnderbarrelData/    # Underbarrel attachments
        ├── UniqueData/         # Legendary/unique data
        └── WeaponStats/        # Base stat definitions

12.7 GameData System

GameData/
├── Activities/             # Activity/event system
├── Animation/              # Animation configs
├── Audio/                  # Audio settings
├── Balance/                # Game balance tables
│   └── Structs/
│       ├── Struct_ChallengeReward_ECHOTokens
│       └── Struct_BossReplay_Costs
├── Cinematics/             # Cinematic triggers
├── Damage/                 # Damage system
│   └── StatusEffects/      # Status effect definitions
├── DataTables/             # Generic data tables
│   └── Structs/
│       ├── Struct_FloatColumn
│       └── Struct_BaseDamage
├── Discovery/              # Discovery/exploration system
├── Globals/                # Global game settings
├── Impacts/                # Impact effects
├── Input/                  # Input bindings
├── Loot/                   # Loot system
│   ├── Balance/
│   │   └── DataTables/
│   │       ├── Struct_EnemyDrops
│   │       └── Struct_DedicatedDropProbability
│   └── LootSchedule/
├── Lootables/              # Lootable containers
├── Map/                    # Map data
├── Missions/               # Mission definitions
├── StatusEffects/          # Status effect data
├── WaypointPath/           # Navigation paths
└── WorldPainter/           # World generation

12.8 AI System

AI/
├── ArmyBandit/             # Bandit enemy faction
├── ArmyOrder/              # Order enemy faction
├── Bosses/                 # Boss enemies
│   ├── GrassBoss/
│   ├── Guardian/
│   ├── MountBoss/
│   ├── ShatterBoss/
│   ├── TKBoss/
│   └── _Shared/
├── Creatures/              # Non-humanoid enemies
├── Critters/               # Small creatures
├── NPC/                    # Non-enemy NPCs
└── _Shared/                # Shared AI resources

12.9 File Naming Conventions

Prefix Type Example
Struct_* Structure definitions Struct_EnemyDrops
DT_* Data Tables DT_WeaponStats
Body_* Body/mesh definitions Body_Pistol_01
DST_* Destruction definitions DST_Barrel
M_* Materials M_Metal_Base
MI_* Material Instances MI_Weapon_Red
MF_* Material Functions MF_Damage_Flash
AS_* Animation Sequences AS_Reload
Script_* Blueprint scripts Script_WeaponFire
StatusEffect_* Status effects StatusEffect_Burn

12.10 Weapon Part Types

From NexusConfigStoreInventory in DefaultGame.ini:

12.10.1 Core Weapon Parts

Part Description
body Main weapon body
body_acc Body accessories
body_mag Body magazine attachment
body_ele Body elemental
body_bolt Bolt mechanism
barrel Weapon barrel
barrel_acc Barrel accessories
barrel_licensed Licensed barrel variants
magazine Magazine
magazine_acc Magazine accessories
magazine_borg Borg magazine type
magazine_ted_thrown Tediore thrown magazine

12.10.2 Attachment Parts

Part Description
scope Optical scopes
scope_acc Scope accessories
rail Rail attachments
bottom Bottom attachments
grip Weapon grip
foregrip Forward grip
underbarrel Underbarrel attachment
underbarrel_acc Underbarrel accessories
underbarrel_acc_vis Visible underbarrel accessories

12.10.3 Manufacturer-Specific

Part Description
tediore_acc Tediore accessories
tediore_secondary_acc Tediore secondary accessories
hyperion_secondary_acc Hyperion secondary accessories
turret_weapon Turret weapon parts

12.10.4 Element & Augments

Part Description
element Primary element
secondary_ele Secondary element
secondary_ammo Secondary ammo type
primary_augment Primary augment slot
secondary_augment Secondary augment slot
enemy_augment Enemy-dropped augment
active_augment Active skill augment
endgame Endgame modifications
unique Unique/legendary parts

12.10.5 Grenade Parts

Part Description
payload Grenade payload
payload_augment Payload augment
stat_augment Stat augment
curative Healing effect
augment General augment
utility_behavior Utility behavior

12.10.6 Class Mod Parts

Part Description
class_mod_body Class mod body
action_skill_mod Action skill modifier
core_augment Core augment
core_plus_augment Core plus augment
passive_points Passive skill points
special_passive Special passive abilities
stat_group1/2/3 Stat groups

12.10.7 Other

Part Description
firmware Firmware upgrades
augment_element Elemental augments
augment_element_resist Elemental resistance
augment_element_nova Nova effect
augment_element_splat Splat effect
augment_element_immunity Elemental immunity
detail Detail parts
skin Weapon skins
vile Vile rarity parts
pearl_elem Pearl elemental
pearl_stat Pearl stat bonus

12.11 Key DataTables

12.11.1 Weapon Naming

Asset Path Contents
/Game/Gear/Weapons/_Shared/NamingStrategies/WeaponNamingStruct Weapon prefix naming
/Game/Gear/Weapons/_Shared/NamingStrategies/DAD_LicensedPart_Table_Struct Daedalus licensed parts
/Game/Gear/Weapons/_Shared/NamingStrategies/TED_PayloadPrefix_Table_Struct Tediore payload prefixes

12.11.2 Balance Data

Asset Path Contents
/Game/Gear/Weapons/_Shared/BalanceData/BarrelData/* Barrel stat modifiers
/Game/Gear/Weapons/_Shared/BalanceData/MagazineData/* Magazine stat modifiers
/Game/Gear/Weapons/_Shared/BalanceData/Rarity/* Rarity tier modifiers
/Game/Gear/Weapons/_Shared/BalanceData/Elemental/* Elemental damage data
/Game/GameData/DataTables/Structs/Struct_BaseDamage Class mod stat tables

12.12 Asset Path Mapping

Game paths use /Game/ prefix:

Game Path Extracted Path
/Game/Gear/Weapons/… OakGame/Content/Gear/Weapons/…
/Script/OakGame.ClassName Engine script class (not extractable)

12.13 Gear Types Found

Type Description
ClassMod Character class modifications
Enhancement Enhancement items
Firmware Firmware upgrades
Gadget Deployable gadgets
Grenade Grenade items
RepairKit Repair kits
Shield Shield equipment

12.14 New Systems in BL4

BL4 introduces several systems not present in BL3:

System Description
Repair Kits Healing/repair items
Enhancements Enhancement slot items
Firmware Firmware upgrade system
Gadgets Turrets, Terminals, Heavy Weapons
Armor Shards Armor shard items
Shield Boosters Shield booster pickups
Hover Drives Vehicle hover drive upgrades
Borg New manufacturer with charge mechanics
Pearl Pearl rarity tier
Vile Vile rarity tier

12.15 Extraction Results

From share/manifest/pak_summary.json:

Field Value
Total Assets 81,097
Stats Count 519
Naming Strategies 3
Manufacturers 9

12.15.1 Manufacturer Codes

BOR, TOR, VLA, COV, MAL, TED, DAD, JAK, ORD

12.15.2 Balance Data Categories

  • firmware
  • Heavy
  • gadget
  • repair_kit
  • unknown
  • grenade
  • shield
  • weapon

12.16 Notes

  1. Structure vs Data: Files named Struct_* are type definitions (schemas), not actual data tables.

  2. IoStore Format: BL4 uses UE5’s IoStore container format with Zen packages.

  3. Missing Data: Per-item balance data is derived from parts at runtime rather than stored in data files.

  4. Compression: BL4 uses Oodle compression for IoStore containers.

12.17 NCS Format (Nexus Config Store)

NCS is Gearbox’s format for storing item pool definitions, part data, and other game configuration that isn’t in standard PAK assets.

12.17.1 Why NCS Matters

Standard PAK extraction returns 0 results for key classes: - ItemPoolDef - Item pool definitions - ItemPoolListDef - Item pool lists - loot_config - Loot configuration

These are stored in NCS format, not as standard uasset files. The class definitions exist in scriptobjects.json, but the actual data lives in NCS.

12.17.2 File Types in NCS Format

Type Description
gbx_ue_data_table Gearbox UE data tables with item definitions
gbxactor Actor definitions with loot references
itempool Item pool definitions (what can drop)
ItemPoolList Item pool list configurations
loot_config Loot configuration with drop rates
Mission + rewards Mission reward definitions
vending_machine Vending machine inventory

12.17.3 gBx Header Format

NCS files use the “gBx” magic header:

Offset  Size  Description
------  ----  -----------
0x00    3     Magic bytes: "gBx" (0x67 0x42 0x78)
0x03    1     Variant byte: '9', '6', 'r', 0xEF, or 0xE0
0x04    ?     Oodle-compressed payload

Variant bytes observed: - 0x39 (‘9’) - Most common - 0x36 (‘6’) - 0x72 (‘r’) - 0xEF - 0xE0

Example locations in pakchunk0-Windows_0_P.pak: - Offset 18327014: 67 42 78 39... (gBx9) - Offset 60169283: 67 42 78 ef... - Offset 78874017: 67 42 78 72... (gBxr)

12.17.4 Compression

NCS uses Oodle compression (version 9): - DLL: oo2core_9_win64.dll - Primary function: OodleLZ_Decompress - Additional: OodleLZ_Compress, Oodle_GetConfigValues

12.17.5 Decompressed Content Format

After decompression, NCS content uses a typed hierarchical format with field|type notation:

12.17.5.1 Type Notation

Suffix Meaning Example
\|map Nested map/object children\|map
\|leaf: String leaf value tags\|leaf:
\|leaf:typename Typed leaf damagesource\|leaf:damagesource
\|empty Boolean/empty flag newobjective\|empty

12.17.5.2 Known Field Names (71 total)

Top-level Structure: - gbx_sections|map - Gearbox sections mapping - children|map - Nested child objects - dependencies|map - Asset dependencies - generateddependencies|map - Generated dependencies - sections|map - General sections - configs|map - Configuration data - attributes|map - Attribute data

Damage System: - damagesource|leaf:damagesource - Damage source reference - damagesource|map - Damage source mapping - damagetags|leaf: - Damage tags - hitdamagesource|leaf:damagesource - Hit damage source - damagesourceoverride|leaf:damagesource - Override - reflecteddamagetags|leaf: - Reflected damage tags - reflectedprojectiledamagetags|leaf: - Projectile reflection - maxchargedamagetags|leaf: - Max charge damage - overheatdamagetags|leaf: - Overheat damage - repairkitdamagetags|leaf: - Repair kit damage - lessthanthresholddamagetags|leaf: - Threshold damage - playerdamagetags|leaf: - Player damage

Activity/Area System: - activityareaactortags|leaf: - Activity area actor tags - activityareatags|leaf: - Activity area tags - areatags|leaf: - Area tags - requiredactivityareatags|leaf: - Required activity area - requiredactivitytags|leaf: - Required activity - excludedactivityareaactortags|leaf: - Excluded activity area actors - excludedactivitytags|leaf: - Excluded activity

Tag System: - tags|leaf: / tags|map - Tag data - excludetags|leaf: / excludetags|map - Exclusion tags - excludeaddtags|leaf: - Add to exclusion - require_tags|leaf: - Required tags - reject_tags|leaf: - Rejected tags - requiredbasetags|leaf: - Required base tags - requiredtags|leaf: - Required tags - excludedbasetags|leaf: - Excluded base tags - excludedplayerdamagetags|leaf: - Excluded player damage

Weapon/Combat: - weaponfire|map - Weapon fire config - effectparameters|map - Effect parameters - effectparametersbysurface|map - Surface effects - effectoverrides|map - Effect overrides - ampedtag|leaf: - Amped tag - tedioreemptytags|leaf: - Tediore empty - tediorehalffullormoretags|leaf: - Tediore half+

Mission System: - invisiblemissiontypes|leaf: - Invisible missions - poamissiontypes|leaf: - POA missions - primarytrackedmissiontypes|leaf: - Primary tracked - temporarytrackedmissiontypes|leaf: - Temporary tracked - worldeventmissiontypes|leaf: - World events - missionfailsafetimerpickuptypes|leaf: - Failsafe timer

UI/Display: - display_items|map - Display items - pips|map - Pip display - wheelsetups|map - Wheel UI setups - loaded_input_actions|map - Input actions - mat26_augersight|map - Auger sight material

Other: - stats|leaf: - Statistics data - apply|leaf: - Apply action - remove|leaf: - Remove action - remove_states|leaf: - Remove states - criteria|map - Criteria conditions - entry_points|map - Entry points - exit_points|map - Exit points - exclusive|leaf: - Exclusive flag - alias_nodes|map - Alias nodes - factdependencies|map - Fact dependencies - data|leaf:damagesource - Data reference - newobjective|empty - New objective flag - momentsuegarden|empty - Moments UE garden - checkleavenoescaperoom01|empty - Escape room check

12.17.6 Hash Function

Field names are hashed using FNV-1a 64-bit: - Offset basis: 0xcbf29ce484222325 - Prime: 0x100000001b3

12.17.7 SerialIndex in NCS

The SerialIndex structure maps parts to their serialization indices:

Offset  Size  Description
------  ----  -----------
0x00    1     Category (weapon platform)
0x01    1     Scope/Status flags
0x02    2     Index (little-endian)

Important: NCS indices are runtime slot positions, NOT the serial encoding indices used in item serials. The manifest’s alphabetical indices are used for serial encoding.

12.17.8 NCS Parser Tool

A community parser exists (Cr4nkSt4r’s NcsParser.exe): - Loads Oodle DLL dynamically - Decodes function names from XOR-encoded strings (key: 0xA7) - Outputs JSON using nlohmann JSON v3.12.0 - Requires oo2core_9_win64.dll from game files

12.17.9 Implementation Notes

To parse NCS files in Rust: 1. Use oodle-safe crate with game’s Oodle DLL 2. Read gBx header to get compressed/decompressed sizes 3. Call OodleLZ_Decompress on payload 4. Parse decompressed content using field|type notation 5. Use FNV-1a hash for field name lookups

Extracted from BL4 game files using retoc and uextract tools.