The determination of an event will vary by contract, but are all external sources of validation, listed in the contract up front. For example, the moon landing resolves to yes if NASA announces by X date. GDP is resolved by Bureau of Economic Analysis, Inflation by the Bureau of Labor Statistics, and so on.

Generally, event contracts are legal contracts technically. We have a team that spent a ton of time developing templates to incorporate all types of events (hard problem). Here's an example definition: https://kalshi-public-docs.s3.amazonaws.com/regulatory/ruleb...