Marathon: How to Increase Inventory Space – Season 2 Vault & Backpack Guide

The Short Answer

Two separate limits are squeezing you and they upgrade in completely different ways. Your Vault (the out-of-raid stash) grows through the Expansion nodes in the CyberAcme faction tree — bought with Credits plus rare materials like Unstable Diodes and Unstable Gunmetal. Your backpack (in-raid carry) does not have a permanent upgrade tree at all: capacity comes from the backpack item you have equipped, bought from the Armory, earned from faction contracts, or looted in-raid from high-tier weapon lockers and dead runners. In Season 2, a fully upgraded Vault tops out at 512 slots, up from Season 1 — and Bungie increased faction progression rates, so you reach those Expansion nodes faster than you did at launch.

What Season 2 Changed (Verified July 2026)

Marathon is on Season 2: Nightfall, live since 2 June 2026 and running to 22 September 2026, 17:00 UTC. Current build is Update 1.1.5 (21 July 2026). For storage specifically, three things changed and they all matter:

• Max Vault size went up. Bungie’s own “Launch, Learnings, and What’s Next” post confirms they expanded the max Vault size for Season 2; Season 2 breakdowns put a fully upgraded Vault at 512 slots. Base capacity before upgrades was 160 items at launch, and Bungie has not published a revised base figure — so treat 160 as the starting point but the ceiling as much higher than it was.
• Faction progression is faster. The same post confirms increased progression rates for both faction and Runner levels in Season 2. Practically: the CyberAcme rank gate in front of your first Expansion arrives sooner than it did in Season 1.
• Expansions were wiped. The 1 June wipe cleared Runner level, faction levels and upgrades, contracts, Credits and all Vault contents. Vault Expansion is seasonal — you re-buy it every season. If you are staring at a tiny Vault in July, that is why.

Also new in Nightfall: The Cradle, a shell stat system where you convert loot into Energy and spend skill points across six stats, freely reallocatable during the season. It is relevant here because it gives your junk loot a second use besides selling — feeding the Cradle is now a legitimate alternative to hoarding marginal gear in a full Vault.

Step 1: Rush the First Two CyberAcme Expansions

CyberAcme is not just ammo and utilities — it owns Vault Expansion. The path:

• Open the Factions screen from the hub.
• Select CyberAcme.
• Go to Upgrades.
• Find the node labelled Expansion / Vault Expansion, near the early core upgrades.

You need a modest CyberAcme rank before the first Expansion unlocks, which means running a few CyberAcme contracts first. Once unlocked, each level permanently (for the season) adds rows of Vault storage. Community documentation of the pre-Season-2 implementation describes five Expansion levels, each costing Credits plus rare materials, with the cost climbing steeply at higher tiers. Bungie has not published per-level cost tables in patch notes, so treat any specific Credit figure you see as community-sourced rather than official.

Practical advice: buy Expansion 1 the moment you can, and Expansion 2 shortly after. Those two are the best value in the game for long-term comfort. You can track the upgrade so its required materials get highlighted in-raid, which turns “I need Unstable Diodes eventually” into a visible objective while you loot.

The mistake that costs you the most time

Spending Unstable Diodes or Unstable Gunmetal on a flashy weapon mod before your first Expansion. Those materials gate the upgrade, and re-farming them takes several runs. Weapons get replaced constantly; Vault space does not.

Step 2: Know When to Stop Buying Expansions

Expansions 3 and up get expensive fast. My rule:

• Buy Expansion 1 and 2 immediately.
• Only push to 3+ once you are consistently sitting at 80–90% of your current cap and you are not hoarding obvious junk.

Because the whole thing resets each season, over-investing late in a season is money you will not get back. With Season 2 ending 22 September, anything you buy in the final weeks is short-lived — that is the moment to spend Credits on gear and Cradle progression instead, exactly as our wipe-week spending breakdown argued last cycle.

Keeping the Vault from re-cluttering

• Set a minimum rarity line and scrap or sell anything below it unless it carries a mod you specifically want.
• Cap backup weapons at two or three per slot type. Six half-built rifles is not a build library, it is clutter.
• Cap common materials. Keep a comfortable stack, sell the surplus.
• Do a five-minute prune every few sessions rather than a panicked purge when you hit the cap and start making bad decisions under pressure.

Step 3: Backpacks Are Items, Not Upgrades

This is the part most players get wrong. There is no permanent backpack-capacity node in any faction tree, and nothing in the Cradle grants it either. Carry capacity comes from the bag you have equipped, and bigger bags come from:

• The Armory, bought with Credits — more tiers appear as your faction rank rises.
• Faction contract rewards.
• In-raid loot — high-tier weapon lockers, and off dead runners.

Expect the first meaningful upgrade to cost a few thousand Credits. It hurts early, and it is worth it if you loot aggressively.

The Sponsored-kit catch

Sponsored loadouts come with their own baseline backpack — buying a big bag in the Armory does not upgrade them. You can, however, find an enhanced backpack mid-raid and equip it on the spot, even on a Sponsored run. That is the cheapest way to run a heavy loot route without risking your own stash: take the free kit, upgrade the bag in the field.

Step 4: In-Raid Triage

Even a maxed Vault will not save you from a bad bag. Rank items by value per slot:

Drop from the bottom up. Ditching a mediocre rifle for one stack of a gated material is almost always correct — the material unlocks an upgrade, the rifle gets replaced next session. Beyond that: consolidate partial stacks of meds and ammo, do not carry redundant ammo types, and once your bag is full of high-value loot near an extraction, stop looting entirely and leave.

The Order I Would Follow on a Fresh Season

1. First sessions: run CyberAcme contracts until Expansion 1 unlocks. Buy it immediately.
2. Next: farm specifically for Expansion 2’s Credits and materials, with the upgrade tracked so the game highlights what you need.
3. Then: push the contracts that open Armory access and buy your first enhanced backpack.
4. Throughout: prune aggressively, feed marginal loot into the Cradle rather than storing it, and never let low-value items hold permanent Vault real estate.

For the full seasonal routing — which contracts to run in what order, and where your XP is actually going — see our Season 2 vault management and XP routing guide. If you want the faction-node shortlist first, the best faction upgrades guide covers it, and everything else Marathon lives on the Marathon hub.

FAQ

What is the maximum Vault size in Season 2?

512 slots at full upgrade, per Season 2 breakdowns following Bungie’s confirmation that max Vault size was expanded for Nightfall. Base capacity at launch was 160 items; Bungie has not published a new base figure.

Do Vault Expansions carry over between seasons?

No. Faction levels and upgrades wipe at the season boundary, so Expansion must be re-purchased each season. The next wipe lands with Season 3 on 22 September 2026.

Can I permanently upgrade my backpack?

No. Backpack capacity is item-based. You buy bigger bags from the Armory, earn them from contracts, or loot them in-raid. There is no skill-tree node for it.

Why is my Vault suddenly full again after Season 2 started?

Because the 2 June wipe reset your Expansion levels along with everything else, dropping you back to base capacity. Re-buying Expansion 1 and 2 through CyberAcme is the fix, and faster faction progression in Nightfall means it takes fewer runs than it did in Season 1.