T.bigint

A scalar. No bare form — same reasoning as T.string: there's no natural bound to fuzz to, so .whereby({ min, max }) is required.

T.bigint.whereby({ min: 0n, max: 1000n });
T.bigint.whereby({ min: { value: 0n, exclusive: true }, max: 1000n });

T.bigint.as(produce) layers a custom producer over the schema — see T.opaque.