Every object is fingerprinted by its sorted key list, so the same shape appearing in three places becomes one shared type instead of three copies. A property is optional when it is missing from some instances of that shape, and nullable when null appears among its values. With literal-union inference on, a string property whose values repeat from a small closed set (for example paid, shipped, refunded) is emitted as a union of literals rather than a bare string. Numbers are all treated as 64-bit floats because JSON does not distinguish integers from decimals, except in Python and Go where a whole-number property becomes int / int64.