zod

4.4.0

This is a minor release with a wide set of correctness and soundness fixes. Some fixes intentionally make Zod stricter, so code that depended on previously accepted invalid or ambiguous inputs may need small updates.

Potentially breaking bug fixes

Tuple defaults now materialize output values correctly

Fixed in #5661. Tuple parsing now more accurately reflects defaults, optional tails, explicit undefined, and under-filled inputs. The headline behavior is that defaults in tuple positions now properly appear in parsed output.

const schema = z.tuple([
  z.string(),
  z.string().default("fallback"),
]);

schema.parse(["a"]);
// ["a", "fallback"]

Trailing optional elements that are absent still stay absent; they are not filled with undefined.

const schema = z.tuple([
  z.string(),
  z.string().optional(),
]);

schema.parse(["a"]);
// ["a"]

But explicit undefined values supplied by the caller are preserved.

schema.parse(["a", undefined]);
// ["a", undefined]

When optional elements appear before later defaults, the parsed tuple is now dense so array operations behave predictably.

const schema = z.tuple([
  z.string(),
  z.string().optional(),
  z.string().default("fallback"),
]);

schema.parse(["a"]);
// ["a", undefined, "fallback"]