diff --git a/scripts/build/deps/webkit.ts b/scripts/build/deps/webkit.ts
index c6e0193955dc..394ead929511 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 = "fb1167ebf2cb9edc1f6771a2c11771b024693ae0";
+export const WEBKIT_VERSION = "autobuild-preview-pr-752-98c438b4";
 
 /**
  * WebKit (JavaScriptCore) — the JS engine.
diff --git a/test/js/bun/jsc/frozen-array-representation.test.ts b/test/js/bun/jsc/frozen-array-representation.test.ts
new file mode 100644
index 000000000000..e0fc3f04bced
--- /dev/null
+++ b/test/js/bun/jsc/frozen-array-representation.test.ts
@@ -0,0 +1,332 @@
+import { describeArray, describe as describeObject } from "bun:jsc";
+import { describe, expect, test } from "bun:test";
+import { bunEnv, bunExe } from "harness";
+
+// Object.freeze / seal / preventExtensions and a read-only "length" keep the elements of an
+// array in the ArrayStorage vector (oven-sh/bun#44305). Before the fix every element moved
+// into the sparse map: the vector length dropped to 0 and every read became a hash lookup.
+
+function vectorLength(a: unknown[]): number {
+  const m = /vector length: (\d+)/.exec(describeArray(a));
+  if (!m) throw new Error(`no vector length in ${describeArray(a)}`);
+  return Number(m[1]);
+}
+
+function ints(n: number): number[] {
+  return Array.from({ length: n }, (_, i) => i);
+}
+
+const locks: [string, (a: unknown[]) => unknown[]][] = [
+  ["Object.freeze", a => Object.freeze(a)],
+  ["Object.seal", a => Object.seal(a)],
+  ["Object.preventExtensions", a => Object.preventExtensions(a)],
+  ["non-writable length", a => Object.defineProperty(a, "length", { writable: false })],
+];
+
+const inputs: [string, () => unknown[], unknown[]][] = [
+  ["int32", () => ints(16), ints(16)],
+  ["double", () => [0.5, 1.5, 2.5], [0.5, 1.5, 2.5]],
+  ["contiguous", () => ["a", null, 1], ["a", null, 1]],
+  ["holey", () => [1, , 3], [1, , 3]],
+  [
+    "length beyond the vector",
+    () => {
+      const a = [1, 2, 3];
+      a.length = 1000;
+      return a;
+    },
+    Object.assign(new Array(1000), [1, 2, 3]),
+  ],
+];
+
+describe("frozen arrays keep their elements in the vector", () => {
+  describe.each(locks)("%s", (name, lock) => {
+    test.each(inputs)("%s", (_input, make, expected) => {
+      "use strict";
+      const a = lock(make());
+      expect(describeObject(a)).toContain("ArrayWithSlowPutArrayStorage");
+      // The vector keeps its capacity, which holds at least every present element.
+      expect(vectorLength(a)).toBeGreaterThanOrEqual(Object.keys(expected).length);
+      expect(a.length).toBe(expected.length);
+      expect(a).toStrictEqual(expected);
+      expect(Object.keys(a)).toEqual(Object.keys(expected));
+      expect(Object.isExtensible(a)).toBe(name === "non-writable length");
+      expect(Object.getOwnPropertyDescriptor(a, "length")!.writable).toBe(
+        name === "Object.seal" || name === "Object.preventExtensions",
+      );
+      // No lock lets the array grow: either the object is non-extensible or its length is read-only.
+      expect(() => {
+        a[a.length] = 1;
+      }).toThrow(TypeError);
+      expect(() => a.push(1)).toThrow(TypeError);
+      expect(a.length).toBe(expected.length);
+      // The structure answers isFrozen / isSealed only for the lock that earned it.
+      expect(Object.isFrozen(a)).toBe(name === "Object.freeze");
+      expect(Object.isSealed(a)).toBe(name === "Object.freeze" || name === "Object.seal");
+    });
+
+    test("an empty array", () => {
+      "use strict";
+      const a = lock(new Array()) as unknown[];
+      expect(Object.isSealed(a)).toBe(name !== "non-writable length");
+      expect(Object.isFrozen(a)).toBe(name === "Object.freeze");
+      expect(() => a.push(1)).toThrow(TypeError);
+      expect(() => {
+        a[0] = 1;
+      }).toThrow(TypeError);
+      expect(Object.hasOwn(a, 0)).toBe(false);
+      expect(a.length).toBe(0);
+      if (name === "Object.freeze" || name === "non-writable length") {
+        expect(() => {
+          a.length = 1;
+        }).toThrow(TypeError);
+        expect(a.length).toBe(0);
+      } else {
+        a.length = 1;
+        expect(a.length).toBe(1);
+        expect(Object.hasOwn(a, 0)).toBe(false);
+      }
+    });
+
+    test("an array that already owns a sparse map entry", () => {
+      "use strict";
+      const b = [1, 2, 3];
+      b[100000] = 4;
+      lock(b);
+      expect(b[0]).toBe(1);
+      expect(b[100000]).toBe(4);
+      expect(b.length).toBe(100001);
+      // A hole between the vector and the map entry cannot be filled on a non-extensible array.
+      if (Object.isExtensible(b)) {
+        b[50000] = 5;
+        expect(b[50000]).toBe(5);
+      } else {
+        expect(() => {
+          b[50000] = 5;
+        }).toThrow(TypeError);
+        expect(Object.hasOwn(b, 50000)).toBe(false);
+      }
+      expect(() => {
+        b[200000] = 5;
+      }).toThrow(TypeError);
+      expect(b.length).toBe(100001);
+    });
+  });
+
+  test("double and contiguous arrays", () => {
+    const d = Object.freeze([0.5, 1.5, 2.5]);
+    expect(vectorLength(d)).toBeGreaterThanOrEqual(3);
+    expect(d[0] + d[1] + d[2]).toBe(4.5);
+    const c = Object.freeze(["a", {}, 1]);
+    expect(vectorLength(c)).toBeGreaterThanOrEqual(3);
+    expect(c[0]).toBe("a");
+  });
+
+  test("frozen semantics hold on the vector", () => {
+    "use strict";
+    const a = Object.freeze(ints(4));
+    expect(() => {
+      a[0] = 9;
+    }).toThrow(TypeError);
+    expect(() => {
+      a[4] = 9;
+    }).toThrow(TypeError);
+    expect(() => a.push(9)).toThrow(TypeError);
+    expect(() => a.pop()).toThrow(TypeError);
+    expect(() => {
+      a.length = 0;
+    }).toThrow(TypeError);
+    expect(() => {
+      delete a[0];
+    }).toThrow(TypeError);
+    expect(Object.getOwnPropertyDescriptor(a, 0)).toEqual({
+      value: 0,
+      writable: false,
+      enumerable: true,
+      configurable: false,
+    });
+    expect(Object.isFrozen(a)).toBe(true);
+    expect([...a]).toEqual([0, 1, 2, 3]);
+    expect(vectorLength(a)).toBeGreaterThanOrEqual(4);
+  });
+
+  test("sealed semantics hold on the vector", () => {
+    "use strict";
+    const a = Object.seal(ints(4));
+    a[0] = 9;
+    expect(a[0]).toBe(9);
+    expect(() => {
+      delete a[0];
+    }).toThrow(TypeError);
+    expect(() => a.pop()).toThrow(TypeError);
+    expect(() => {
+      a.length = 1;
+    }).toThrow(TypeError);
+    expect(a.length).toBe(4);
+    expect(() => a.push(9)).toThrow(TypeError);
+    expect(Object.getOwnPropertyDescriptor(a, 0)).toEqual({
+      value: 9,
+      writable: true,
+      enumerable: true,
+      configurable: false,
+    });
+    expect(Object.isSealed(a)).toBe(true);
+    expect(Object.isFrozen(a)).toBe(false);
+    expect(vectorLength(a)).toBeGreaterThanOrEqual(4);
+  });
+
+  test("a frozen array on the prototype chain rejects inherited writes", () => {
+    "use strict";
+    const proto = Object.freeze(ints(3));
+    const child = Object.create(proto);
+    expect(() => {
+      child[0] = 9;
+    }).toThrow(TypeError);
+    expect(child[0]).toBe(0);
+    expect(Object.hasOwn(child, 0)).toBe(false);
+
+    // Frozen after it became a prototype, with a plain child and an array child with a hole.
+    const late = ints(3);
+    const plainChild = Object.create(late);
+    const arrayChild = [9, , 9];
+    Object.setPrototypeOf(arrayChild, late);
+    Object.freeze(late);
+    expect(() => {
+      plainChild[1] = 9;
+    }).toThrow(TypeError);
+    expect(Object.hasOwn(plainChild, 1)).toBe(false);
+    expect(() => {
+      arrayChild[1] = 9;
+    }).toThrow(TypeError);
+    expect(Object.hasOwn(arrayChild, 1)).toBe(false);
+    expect(arrayChild[1]).toBe(1);
+
+    // Object.setPrototypeOf to an array frozen earlier.
+    const grown = [9, , 9];
+    Object.setPrototypeOf(grown, proto);
+    expect(() => {
+      grown[1] = 9;
+    }).toThrow(TypeError);
+    expect(grown[1]).toBe(1);
+    grown[3] = 3;
+    expect(grown.length).toBe(4);
+
+    // A sealed prototype does not stop the child from shadowing.
+    const sealed = Object.seal([7, 8, 9]);
+    const shadow = Object.create(sealed);
+    shadow[0] = 77;
+    expect(shadow[0]).toBe(77);
+    expect(sealed[0]).toBe(7);
+  });
+
+  test("a store site warmed on a writable non-extensible array rejects a frozen one", () => {
+    function store(a: number[], i: number, v: number) {
+      "use strict";
+      a[i] = v;
+    }
+    const writable = Object.preventExtensions(ints(8));
+    for (let i = 0; i < 100_000; i++) store(writable, i & 7, i);
+    const frozen = Object.freeze(ints(8));
+    for (let i = 0; i < 1000; i++) {
+      expect(() => store(frozen, i & 7, -1)).toThrow(TypeError);
+      store(writable, i & 7, -1);
+    }
+    expect(frozen).toEqual([0, 1, 2, 3, 4, 5, 6, 7]);
+    expect(writable).toEqual([-1, -1, -1, -1, -1, -1, -1, -1]);
+  });
+
+  test("defineProperty on one element moves the array to the sparse map with exact descriptors", () => {
+    const a = Object.seal(ints(3));
+    Object.defineProperty(a, 0, { writable: false });
+    expect(Object.getOwnPropertyDescriptor(a, 0)).toEqual({
+      value: 0,
+      writable: false,
+      enumerable: true,
+      configurable: false,
+    });
+    expect(Object.getOwnPropertyDescriptor(a, 1)).toEqual({
+      value: 1,
+      writable: true,
+      enumerable: true,
+      configurable: false,
+    });
+    expect(vectorLength(a)).toBe(0);
+    expect(() => Object.defineProperty(a, 1, { configurable: true })).toThrow(TypeError);
+    expect(Object.isSealed(a)).toBe(true);
+    expect(Object.isFrozen(a)).toBe(false);
+    // Frozen through the element-wise route: the generic walk, not the structure, answers.
+    Object.defineProperty(a, 1, { writable: false });
+    Object.defineProperty(a, 2, { writable: false });
+    expect(Object.isFrozen(a)).toBe(false);
+    Object.defineProperty(a, "length", { writable: false });
+    expect(Object.isFrozen(a)).toBe(true);
+    const b = Object.preventExtensions([1, 2]);
+    expect(Object.isSealed(b)).toBe(false);
+    Object.defineProperty(b, 0, { configurable: false });
+    Object.defineProperty(b, 1, { configurable: false });
+    expect(Object.isSealed(b)).toBe(true);
+    expect(Object.isFrozen(b)).toBe(false);
+  });
+
+  test.concurrent("freezing one literal leaves the next literal from the same site writable", async () => {
+    // A separate process: another test file can put this realm in "having a bad time" mode, and
+    // then every array is SlowPutArrayStorage.
+    await using proc = Bun.spawn({
+      cmd: [
+        bunExe(),
+        "-e",
+        `const { describe } = require("bun:jsc");
+         function make() { return [1, 2, 3, 4]; }
+         function build(n) { const a = []; for (let i = 0; i < n; i++) a.push(i); return a; }
+         let slow = 0;
+         for (let i = 0; i < 200; i++) {
+           const a = Object.freeze(make());
+           const b = make();
+           b[0] = 9;
+           b.push(5);
+           if (b.join() !== "9,2,3,4,5" || a.join() !== "1,2,3,4") throw new Error("bad values");
+           if (describe(b).includes("SlowPutArrayStorage")) slow++;
+           Object.freeze(build(8));
+           if (describe(build(8)).includes("SlowPutArrayStorage")) slow++;
+         }
+         console.log(slow);`,
+      ],
+      env: bunEnv,
+      stderr: "pipe",
+    });
+    const [stdout, stderr, exitCode] = await Promise.all([proc.stdout.text(), proc.stderr.text(), proc.exited]);
+    expect(stderr).toBe("");
+    expect(stdout).toBe("0\n");
+    expect(exitCode).toBe(0);
+  });
+
+  test.concurrent("freezing Array.prototype keeps it blank", async () => {
+    // A separate process, so the rest of the test run keeps a writable Array.prototype.
+    await using proc = Bun.spawn({
+      cmd: [
+        bunExe(),
+        "-e",
+        `const { describe } = require("bun:jsc");
+         Object.freeze(Array.prototype);
+         let threw = false;
+         try { Array.prototype.push.call(Array.prototype, 1); } catch (e) { threw = e instanceof TypeError; }
+         // Reflect.set reports the rejection whatever the strictness of this script is.
+         const rejected = [Reflect.set(Array.prototype, 0, 1), Reflect.set(Array.prototype, "length", 1)].map(ok => !ok);
+         console.log(JSON.stringify({ threw, rejected, own: Object.hasOwn(Array.prototype, 0), length: Array.prototype.length, frozen: Object.isFrozen(Array.prototype), blank: describe(Array.prototype).includes("ArrayClass") }));`,
+      ],
+      env: bunEnv,
+      stderr: "pipe",
+    });
+    const [stdout, stderr, exitCode] = await Promise.all([proc.stdout.text(), proc.stderr.text(), proc.exited]);
+    expect(stderr).toBe("");
+    expect(JSON.parse(stdout)).toEqual({
+      threw: true,
+      rejected: [true, true],
+      own: false,
+      length: 0,
+      frozen: true,
+      blank: true,
+    });
+    expect(exitCode).toBe(0);
+  });
+});