Case odds, StatTrak and the trade-up contract: the rules Valve actually publishes

The published rules paint a different picture than the guesswork that dominates the Counter-Strike 2 community.

Valve confirms case odds

Valve publishes the probability of each rarity for any given case using the odds printed on the outside of the case itself. Players can check the odds on the case, look up the case in Counter-Strike 2, or search for the case name on community forums for a record of the odds. Community sites exist that discuss case odds for Counter-Strike 2.

Valve does not publish an expected value or probability distribution for case openings. Players are confined to using the printed odds on the outside of the case to build their own trade-up or trading models.

For one casual player, this adds up to a steep learning curve, as most community guesses are wrong and after-case-opening arithmetic ends up not reflecting Valve’s rules.

A Counter-Strike case requires a key to open

Valve’s official materials say that a key is required to open a weapon case in Counter-Strike 2. Each key is associated with a specific case, and players must have both a key and the matching case that has yet to be opened.

Valve’s support article for Counter-Strike 2 weapons, cases, and keys gives instructions on how to open a case but does not publish case odds or the expected value of any case for the player. Valve's materials do not describe stockpiling keys to mix and match weapons from different cases.

Valve’s official support page does not affirm or deny the sale of case keys, nor does it give information on how to calibrate the general value of a case key for future trades.

StatTrak adds value to eligible weapon skins

StatTrak is a separate weapon skin property that appears on eligible weapon skins as an individual characteristic. StatTrak skins are not poolable with non-StatTrak skins. The presence or absence of StatTrak has no impact on the wear associated with a given weapon, and StatTrak does not independently add any wear-based value to the skinned weapon. StatTrak appears on eligible weapon skins.

A common mistake that traps many players is thinking you can combine StatTrak skins with non-StatTrak skins in one contract. When a player uses a trade-up contract, they can use either their StatTrak skins or their non-StatTrak skins, but not a combination of the two. In addition, StatTrak skins cannot be used with non-StatTrak skins in a single trade-up contract.

What a trade-up contract is

A trade-up contract allows a CS2 player to exchange 10 normal or StatTrak weapon skins of the same rarity for one weapon skin of the next highest rarity from one of the weapon collections used in the contract. The contract does not reset the wear, and the resulting skin is not randomly generated from that collection of weapon skins. Instead, the wear of the resulting skin is determined by the wear of the 10 input skins, and the weapon skin output is drawn from the weapon collection used in the contract.

Valve has a short set of specific rules around trade-up contracts:

• Normal weapon skins cannot be used in a Trade Up Contract with StatTrak weapon skins, and vice versa.
• A Trade Up Contract requires all ten weapons to be the same weapon rarity and either normal or StatTrak.
• A player uses a Trade Up Contract by left-clicking an eligible weapon and selecting “Use With Trade Up Contract.”

Again, wear matters: a trade-up will never yield a skin with a wear that is better than the wear of the inputs, even if the resulting skin is rarer than the combination of input skins.

So a trade-up contract is a disciplined way to upgrade the value of a skin, even if the actual process of combining skins can be a bit tedious to do, especially with a statistical focus. Valve software handles the task of combining skins, leaving players on paper with a resulting skin that is better than the input combination, but derived directly from the wear process.

Valve’s support page and developers documentation do not specify which cases will accept a trade-up contract, so players are on their own in working every possible combination of case-keys and weapon collections as they sort through their Counter-Strike 2 inventory.

Output wear is determined by the wear of the input skins

Valve’s developers documentation confirms that wear calculations have a key trap for players that is not obvious: The wear of the output weapon skin is derived from the wear of the input weapon skins.

Valve documentation notes that the output skin's wear reflects the wear of the input skins. Valve's documentation says the resulting skin is not randomly generated, and its wear is determined by the wear of the input skins.

Valve’s trade-up documentation also specifies that StatTrak is a separate property of eligible skinned weapons and confirms that StatTrak and non-StatTrak skins cannot be used in combination in a single trade-up contract.

The wear calculation for trade-ups is the aspect of Valve’s system that has the greatest chance of surprising players, as output wear is derived from the inputs rather than freshly rolled.

Expected value is missing

Expected value for case openings or trade-up contracts is not included in the official Valve documentation. Players should interpret Valve’s guidance on case opening and trade-up contracts in light of the rarity odds that are published on the outside of each case.

Valve’s documentation does not include guidance for optimizing trade-up contracts for higher-value skins, chasing case openings with better odds, or maintaining an inventory balance between skins with StatTrak and without StatTrak.

The lack of generalized guidance on the value of any given case or the expected value of a trade-up means that players are on their own in analyzing trade-ups and optimizing keys and skins for future trades or play.

With a given rarity of skins on a weapon case, traders can only estimate the value of a new case, a specific trade-up, or an inventory of skins and keys.