diff --git a/scripts/build/deps/webkit.ts b/scripts/build/deps/webkit.ts
index 7e8ddecce2ac..ed799d872e1d 100644
--- a/scripts/build/deps/webkit.ts
+++ b/scripts/build/deps/webkit.ts
@@ -3,7 +3,7 @@
  * for local mode. Override via `--webkit-version=<hash>` to test a branch.
  * From https://github.com/oven-sh/WebKit releases.
  */
-export const WEBKIT_VERSION = "2e2aa2290fac856d6f451ceacb58f7f5b44dd057";
+export const WEBKIT_VERSION = "autobuild-preview-pr-600-cbbbe00e";
 
 /**
  * WebKit (JavaScriptCore) — the JS engine.
diff --git a/test/js/web/temporal/temporal.test.ts b/test/js/web/temporal/temporal.test.ts
index d2d1deb7044a..401d0f3bd8ee 100644
--- a/test/js/web/temporal/temporal.test.ts
+++ b/test/js/web/temporal/temporal.test.ts
@@ -86,3 +86,86 @@ describe("Temporal core operations", () => {
     expect(() => structuredClone(Temporal.Instant.from("2024-06-15T00:00Z"))).toThrow(DOMException);
   });
 });
+
+// Divergences from V8 found by differential fuzzing. Expected values are what Node 26 / Chromium 148 print.
+describe("Temporal spec conformance", () => {
+  // ToTemporalDate: PrepareCalendarFields, then GetOptionsObject (TypeError), then CalendarDateFromFields
+  // (era resolution and the ISODateWithinLimits check, both RangeError).
+  describe("PlainDate.from rejects a non-object options before it resolves the calendar fields", () => {
+    test.each([
+      [{ year: -271821, month: 2, day: 31 }, RangeError],
+      [{ year: 275760, month: 9, day: 14 }, RangeError],
+      [{ era: "xx", eraYear: 1, month: 1, day: 1, calendar: "gregory" }, RangeError],
+      [{ year: 2024, month: 13, day: 1 }, "2024-12-01"],
+    ] as const)("%j", (bag, withValidOptions) => {
+      for (const options of [null, "constrain", 1, true]) {
+        expect(() => Temporal.PlainDate.from(bag, options as any)).toThrow(TypeError);
+      }
+      // With a real options object the late RangeError (or the constrained date) surfaces.
+      if (typeof withValidOptions === "string") {
+        expect(Temporal.PlainDate.from(bag, {}).toString()).toBe(withValidOptions);
+      } else {
+        expect(() => Temporal.PlainDate.from(bag, {})).toThrow(withValidOptions);
+      }
+    });
+
+    test("the bag is read first, and PrepareCalendarFields errors still win", () => {
+      const reads: PropertyKey[] = [];
+      const bag = new Proxy(
+        { year: -271821, month: 2, day: 31 },
+        { get: (t, k, r) => (reads.push(k), Reflect.get(t, k, r)) },
+      );
+      expect(() => Temporal.PlainDate.from(bag, null as any)).toThrow(TypeError);
+      expect(reads).toEqual(["calendar", "day", "month", "monthCode", "year"]);
+      expect(() => Temporal.PlainDate.from({ year: 2024, month: 0, day: 1 }, null as any)).toThrow(RangeError);
+    });
+  });
+
+  test("rounding to weeks accepts a window edge on the minimum PlainDate", () => {
+    const later = Temporal.PlainDate.from("2016-02-29");
+    const nearMin = Temporal.PlainDate.from("-271821-04-20");
+    const results = Object.fromEntries(
+      ["trunc", "floor", "expand", "halfExpand"].map(roundingMode => [
+        roundingMode,
+        later.since(nearMin, { smallestUnit: "weeks", roundingMode: roundingMode as Temporal.RoundingMode }).toString(),
+      ]),
+    );
+    expect(results).toEqual({
+      trunc: "P14288122W",
+      floor: "P14288122W",
+      expand: "P14288123W",
+      halfExpand: "P14288123W",
+    });
+    expect(nearMin.until(later, { smallestUnit: "weeks" }).toString()).toBe("P14288122W");
+    expect(later.since(nearMin, { smallestUnit: "days", roundingIncrement: 7 }).toString()).toBe("P100016854D");
+    expect(
+      Temporal.Duration.from({ days: -100016860 })
+        .round({ relativeTo: later, smallestUnit: "weeks", roundingMode: "trunc" })
+        .toString(),
+    ).toBe("-P14288122W");
+    // An edge that is really below the minimum still throws (here: the exact minimum as operand).
+    expect(() => later.since("-271821-04-19", { smallestUnit: "weeks" })).toThrow(RangeError);
+  });
+
+  describe("era codes match the lowercase CLDR identifiers exactly", () => {
+    test.each([
+      ["gregory", "CE"],
+      ["gregory", "Bce"],
+      ["gregory", "AD"],
+      ["japanese", "Reiwa"],
+      ["hebrew", "AM"],
+    ])("%s rejects %s", (calendar, era) => {
+      expect(() => Temporal.PlainDate.from({ era, eraYear: 1, month: 1, day: 1, calendar })).toThrow(RangeError);
+    });
+
+    test("lowercase codes and aliases resolve", () => {
+      expect(Temporal.PlainDate.from({ era: "ce", eraYear: 1, month: 1, day: 1, calendar: "gregory" }).toString()).toBe(
+        "0001-01-01[u-ca=gregory]",
+      );
+      expect(Temporal.PlainDate.from({ era: "ad", eraYear: 1, month: 1, day: 1, calendar: "gregory" }).era).toBe("ce");
+      expect(
+        Temporal.PlainDate.from({ era: "reiwa", eraYear: 1, month: 5, day: 1, calendar: "japanese" }).toString(),
+      ).toBe("2019-05-01[u-ca=japanese]");
+    });
+  });
+});