diff --git a/example/src/root.zig b/example/src/root.zig
index 6f50a7f..65abcaf 100644
--- a/example/src/root.zig
+++ b/example/src/root.zig
@@ -523,8 +523,10 @@ pub fn run(allocator: std.mem.Allocator, io_optional: ?std.Io) !void {
     });
 
     if (io_optional) |io| {
-        const now_zdt = try Temporal.Now.zonedDateTimeISO(io);
+        const now_zdt = try Temporal.Now.zonedDateTimeISO(allocator, io);
         defer now_zdt.deinit();
+        const now_tz_id = try Temporal.Now.timeZoneId(allocator);
+        defer allocator.free(now_tz_id);
         std.log.info(
             \\Now Coverage
             \\ - timeZoneId(): {s}
@@ -532,7 +534,7 @@ pub fn run(allocator: std.mem.Allocator, io_optional: ?std.Io) !void {
             \\
             \\
         , .{
-            Temporal.Now.timeZoneId(),
+            now_tz_id,
             try now_zdt.toString(allocator, .{}),
         });
     }
diff --git a/src/Instant.zig b/src/Instant.zig
index 612b2a2..5c1b958 100644
--- a/src/Instant.zig
+++ b/src/Instant.zig
@@ -62,6 +62,7 @@ pub fn fromEpochMilliseconds(epoch_ms: i64) !Instant {
 /// See: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Temporal/Instant/fromEpochNanoseconds
 pub fn fromEpochNanoseconds(epoch_ns: i128) !Instant {
     const parts = abi.toI128Nanoseconds(epoch_ns);
+
     return wrapInstant(abi.c.temporal_rs_Instant_try_new(parts));
 }
 
diff --git a/src/Now.zig b/src/Now.zig
index 9ad8ec5..4e84e7d 100644
--- a/src/Now.zig
+++ b/src/Now.zig
@@ -79,17 +79,28 @@ pub fn plainTimeISO(io: std.Io) !PlainTime {
 
 /// Returns a time zone identifier representing the system's current time zone.
 ///
+/// The caller owns the returned slice and must free it with `allocator`.
+///
+/// TODO: Detect the system's actual IANA time zone instead of always returning
+/// "UTC". This requires platform-specific logic:
+///   - Linux/macOS: resolve the `/etc/localtime` symlink to `.../zoneinfo/<Area>/<City>`.
+///   - Windows: read the time zone from the registry and map the Windows zone
+///     name to an IANA identifier via the CLDR `windowsZones` table.
+///   - WASI: no host time zone is available; "UTC" is the only honest answer.
+///
 /// See: [MDN Temporal.Now.timeZoneId](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Temporal/Now/timeZoneId)
-pub fn timeZoneId() []const u8 {
-    return "UTC";
+pub fn timeZoneId(allocator: std.mem.Allocator) ![]const u8 {
+    return allocator.dupe(u8, "UTC");
 }
 
 /// Returns the current date and time as a [`Temporal.ZonedDateTime`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Temporal/ZonedDateTime) object, in the ISO 8601 calendar and the specified time zone.
 ///
 /// See: [MDN Temporal.Now.zonedDateTimeISO](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Temporal/Now/zonedDateTimeISO)
-pub fn zonedDateTimeISO(io: std.Io) !ZonedDateTime {
+pub fn zonedDateTimeISO(allocator: std.mem.Allocator, io: std.Io) !ZonedDateTime {
     const now = try instant(io);
-    const time_zone = try ZonedDateTime.TimeZone.init(timeZoneId());
+    const tz_id = try timeZoneId(allocator);
+    defer allocator.free(tz_id);
+    const time_zone = try ZonedDateTime.TimeZone.init(tz_id);
     return ZonedDateTime.fromEpochNanoseconds(now.epochNanoseconds(), time_zone);
 }
 
@@ -167,12 +178,13 @@ test plainTimeISO {
     try std.testing.expect(t.second() < 60);
 }
 test timeZoneId {
-    const tz = timeZoneId();
+    const tz = try timeZoneId(std.testing.allocator);
+    defer std.testing.allocator.free(tz);
     try std.testing.expectEqualStrings("UTC", tz);
 }
 test zonedDateTimeISO {
     const io = std.testing.io;
-    const zdt = try zonedDateTimeISO(io);
+    const zdt = try zonedDateTimeISO(std.testing.allocator, io);
     defer zdt.deinit();
 
     std.log.info("{d}", .{zdt.epochNanoseconds()});