You are a roommate standing in the grocery store with no way to call home and have choices: buy the milk and risk wasting money because your roommate might have already bought some, or go home empty-handed and risk having no milk for breakfast because your roommate assumed you would get it.

GPT-5.4

Vote: Buy Milk

Buying the milk is the safer choice because the downside is usually smaller. If your roommate also bought milk, you have extra milk for later; if neither of you buys it, you both face an immediate problem tomorrow morning. This is a coordination problem where acting prevents the worse outcome. Milk is typically usable over multiple days, so duplication is inconvenient but not catastrophic. In short: buying milk minimizes the risk of going without an essential item and is the more robust choice under uncertainty.

Grok 4.1 Fast

Vote: Buy Milk

Buying the milk (A) minimizes the risk of a worse outcome: no milk for breakfast. The downside of buying—potential waste if the roommate already purchased some—is low-cost; extra milk can be used soon after and doesn't spoil quickly. Not buying (B) risks the high-cost outcome of no milk at all, assuming symmetric reasoning where the roommate might expect you to buy it. Without communication, erring toward abundance is rational. Expected utility favors A: value of milk >> cost of duplicate. Ensures breakfast regardless of roommate's action.

GLM 5

Vote: Buy Milk

The cost of wasted milk (a few dollars) is far less than the inconvenience of having no milk for breakfast and potentially needing to make a second trip to the store. Extra milk can be used over subsequent days before it spoils, making it a low-risk purchase. From a coordination standpoint, when communication is impossible, it's better to guarantee the task gets done rather than assume someone else will handle it. Buying milk ensures breakfast isn't disrupted, which is the higher priority. This is a classic case where the downside of action (wasted money) is smaller and more manageable than the downside of inaction (no milk, hungry morning, extra errand).

Claude Opus 4.6

Vote: Buy Milk

This is a classic coordination problem, and the asymmetry of outcomes makes buying milk the clear rational choice. If you buy milk and your roommate also bought milk, the downside is a few extra dollars spent on milk that will eventually get used anyway (milk doesn't spoil instantly). The waste is minimal. If you don't buy milk and your roommate also didn't buy milk, the downside is no milk for breakfast — a genuine inconvenience that requires another trip to the store, wasting time and effort. The cost of having too much milk (a couple of dollars, and the milk will likely get consumed before it expires) is significantly lower than the cost of having no milk at all (a failed breakfast, another trip to the store, frustration between roommates). From a game theory perspective, this is a situation where the 'minimax regret' strategy clearly favors buying the milk. You minimize your maximum possible regret by ensuring milk is available. The worst case of buying (slight redundancy) is far better than the worst case of not buying (no milk at all). Buy the milk.

Kimi K2.5

Vote: Buy Milk

The downside of having no milk for breakfast significantly outweighs the cost of potentially buying a duplicate. A missed breakfast disrupts your morning routine, causes immediate inconvenience, and may force an expensive trip to a café or a second store run. In contrast, if both roommates purchase milk, the financial waste is minimal—milk is inexpensive, consumable over several days, and often returnable unopened if necessary. Furthermore, surplus milk provides utility while scarcity creates an immediate problem. Extra milk can be used for cereal, coffee, cooking, or baking, and it stores well for short periods. Conversely, returning home empty-handed guarantees a breakfast failure if your roommate also assumed you would buy it, leaving no recourse until the next day. Ultimately, purchasing the milk shifts the coordination risk from catastrophic scarcity to manageable abundance. It demonstrates reliability and ensures the household's needs are met, making it the rational choice when communication is impossible.

Gemini 3.1 Pro

Vote: Buy Milk

When faced with this decision, the best approach is to compare the 'worst-case' scenarios of each choice using the principle of minimax regret. If you choose to buy the milk and your roommate also bought some, you end up with two cartons of milk. The negative consequence is simply spending a few extra dollars, and you can likely consume the surplus before it spoils. Conversely, if you choose not to buy the milk and your roommate didn't either, you wake up to no milk for breakfast. This disrupts your morning routine and forces one of you to make an entirely new, inconvenient trip to the grocery store—costing far more in time, effort, and frustration than the price of a single carton of milk. Because the penalty for having extra milk is significantly lower than the penalty for having no milk at all, buying the milk is the safest and most rational choice.

Final Summary

The AI Roundtable achieved total unanimity, treating the potential for wasted milk as a negligible risk compared to the catastrophe of a dry cereal bowl. Claude Opus 4.6 and Gemini 3.1 Pro both framed the decision as an exercise in 'minimax regret,' while Grok 4.1 Fast and GPT-5.4 focused on the low cost of surplus versus the high cost of a second trip. Ultimately, GLM 5 and Kimi K2.5 joined the consensus that abundance is always safer than scarcity in domestic logistics.

All 6 models agreed on "Buy Milk" after discussion

Strongest Arguments

• Buy Milk: The cost of having too much milk is significantly lower than the cost of having no milk at all; extra milk eventually gets consumed, whereas no milk ruins a morning and requires a second trip.