diff --git a/JetStreamDriver.js b/JetStreamDriver.js
index f248e11e..225e26cd 100644
--- a/JetStreamDriver.js
+++ b/JetStreamDriver.js
@@ -1323,7 +1323,7 @@ class AsyncBenchmark extends DefaultBenchmark {
     get runnerCode() {
         return `
         async function doRun() {
-            const benchmark = new Benchmark(${this.iterations});
+            const benchmark = new Benchmark(${JSON.stringify(this.benchmarkArguments)});
             await benchmark.init?.();
             const results = [];
             const benchmarkName = "${this.name}";
@@ -2534,6 +2534,37 @@ let BENCHMARKS = [
 ];
 
 
+const INTL_TESTS = [
+    "DateTimeFormat",
+    "ListFormat",
+    "RelativeTimeFormat",
+    "NumberFormat",
+    "PluralRules",
+];
+const INTL_BENCHMARKS = [];
+for (const test of INTL_TESTS) {
+    const benchmark = new AsyncBenchmark({
+        name: `${test}-intl`,
+        files: [
+            "./intl/src/helper.js",
+            `./intl/src/${test}.js`,
+            "./intl/benchmark.js",
+        ],
+        iterations: 2,
+        worstCaseCount: 1,
+        deterministicRandom: true,
+        tags: ["Javascript", "intl"],
+    });
+    INTL_BENCHMARKS.push(benchmark);
+}
+BENCHMARKS.push(
+    new GroupedBenchmark({
+            name: "intl",
+            tags: ["Javascript", "intl"],
+        }, INTL_BENCHMARKS));
+
+
+
 // SunSpider tests
 const SUNSPIDER_TESTS = [
     "3d-cube",
diff --git a/intl/benchmark.js b/intl/benchmark.js
new file mode 100644
index 00000000..8c835952
--- /dev/null
+++ b/intl/benchmark.js
@@ -0,0 +1,55 @@
+/*
+ * Copyright (C) 2025 Apple Inc. All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
+ * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+ * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE INC. OR
+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
+ * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
+ * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
+ * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
+ * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+class Benchmark {
+  iterationCount;
+  verbose;
+  lastResult;
+  totalLength = 0;
+  expectedMinLength = 0;
+
+  constructor({ iterationCount, verbose = false } = {}) {
+    this.iterationCount = iterationCount;
+    this.verbose = verbose;
+  }
+
+  runIteration() {
+    // See implementations in src/.
+    const { lastResult, totalLength, expectedMinLength } = runTest(
+      this.verbose
+    );
+    this.lastResult = lastResult;
+    this.totalLength += totalLength;
+    this.expectedMinLength = expectedMinLength;
+  }
+
+  validate() {
+    const expectedMinTotalLength = this.expectedMinLength * this.iterationCount;
+    console.assert(
+      this.totalLength >= expectedMinTotalLength,
+      `Invalid totalLength = ${this.totalLength}, expected >= ${expectedMinTotalLength}`
+    );
+  }
+}
diff --git a/intl/src/DateTimeFormat.js b/intl/src/DateTimeFormat.js
new file mode 100644
index 00000000..ee981bf2
--- /dev/null
+++ b/intl/src/DateTimeFormat.js
@@ -0,0 +1,77 @@
+function generateRandomDates(count) {
+  const firstDate = new Date(1800, 11, 5, 13, 6);
+  let currentTimeStamp = firstDate.getTime();
+  const dates = [];
+
+  for (let i = 0; i < count; i++) {
+    dates.push(new Date(currentTimeStamp));
+    currentTimeStamp += 1234569;
+  }
+  return dates;
+}
+
+const DATE_STYLE_OPTIONS = ["full", "long", "medium", "short"];
+const TIME_STYLE_OPTIONS = ["full", "long", "medium", "short"];
+
+function* dateTimeFormatOptions() {
+  for (const locale of LOCALES) {
+    for (const dateStyle of DATE_STYLE_OPTIONS) {
+      for (const timeStyle of TIME_STYLE_OPTIONS) {
+        yield { locale, dateStyle, timeStyle };
+      }
+    }
+  }
+}
+
+function runTest(verbose = false) {
+  let totalLength = 0;
+  let lastFormatResult;
+  let lastFormatPartResult;
+  let lastFormatRangeResult;
+  const dates = generateRandomDates(100);
+  let dateIndex = 0;
+
+  const FORMAT_COUNT = 17;
+  const FORMAT_RANGE_COUNT = 7;
+  for (const { locale, dateStyle, timeStyle } of shuffleOptions(
+    dateTimeFormatOptions
+  )) {
+    const options = { dateStyle, timeStyle };
+    if (verbose) {
+      console.log(locale, JSON.stringify(options));
+    }
+    const formatter = new Intl.DateTimeFormat(locale, options);
+    for (let i = 0; i < FORMAT_COUNT; i++) {
+      let date = dates[dateIndex % dates.length];
+      lastFormatResult = formatter.format(date);
+      totalLength += lastFormatResult.length;
+      if (verbose) {
+        console.log(date, lastFormatResult);
+      }
+      dateIndex++;
+
+      date = dates[dateIndex % dates.length];
+      lastFormatPartResult = formatter.formatToParts(date);
+      for (const part of lastFormatPartResult) {
+        totalLength += part.value.length;
+      }
+      dateIndex++;
+    }
+    let dateRangeStart = dates[0];
+    for (let i = 0; i < FORMAT_RANGE_COUNT; i++) {
+      const date = dates[dateIndex % dates.length];
+      if (dateRangeStart < date) {
+        lastFormatRangeResult = formatter.formatRange(dateRangeStart, date);
+        if (verbose) {
+          console.log(dateRangeStart, date, lastFormatRangeResult);
+        }
+      }
+      dateRangeStart = date;
+    }
+  }
+  return {
+    lastResult: lastFormatResult + lastFormatRangeResult,
+    totalLength,
+    expectedMinLength: 438_000,
+  };
+}
diff --git a/intl/src/ListFormat.js b/intl/src/ListFormat.js
new file mode 100644
index 00000000..9849853c
--- /dev/null
+++ b/intl/src/ListFormat.js
@@ -0,0 +1,47 @@
+const LISTS = [
+  ["One"],
+  ["1", "2"],
+  ["Motorcycle", "Bus", "Car"],
+  LOCALES,
+  new Array(100).fill(9).map((_, index) => index.toString()),
+];
+
+function* listOptions() {
+  const styleOptions = ["long", "short", "narrow"];
+  const typeOptions = ["conjunction", "disjunction", "unit"];
+  for (const locale of LOCALES) {
+    for (const style of styleOptions) {
+      for (const type of typeOptions) {
+        yield { locale, style, type };
+      }
+    }
+  }
+}
+
+function runTest(verbose = false) {
+  let lastResult;
+  let totalLength = 0;
+  const LIST_FORMAT_COUNT = 10;
+  let listIndex = 0;
+  for (const { locale, style, type } of shuffleOptions(listOptions)) {
+    const options = { style, type };
+    if (verbose) {
+      console.log(locale, JSON.stringify(options));
+    }
+    const formatter = new Intl.ListFormat(locale, options);
+    for (let i = 0; i < LIST_FORMAT_COUNT; i++) {
+      const list = LISTS[listIndex % LISTS.length];
+      listIndex++;
+      lastResult = formatter.format(list);
+      totalLength += lastResult.length;
+      const formatPartsResult = formatter.formatToParts(list);
+      if (verbose) {
+        console.log(value, lastResult);
+      }
+      for (const part of formatPartsResult) {
+        totalLength += part.value.length;
+      }
+    }
+  }
+  return { lastResult, totalLength, expectedMinLength: 506_000 };
+}
diff --git a/intl/src/NumberFormat.js b/intl/src/NumberFormat.js
new file mode 100644
index 00000000..6a847214
--- /dev/null
+++ b/intl/src/NumberFormat.js
@@ -0,0 +1,96 @@
+const CURRENCIES = ["USD", "EUR", "JPY", "INR", "NGN"];
+
+const NUMBER_UNITS = [
+  "acre",
+  "bit",
+  "byte",
+  "celsius",
+  "centimeter",
+  "day",
+  "degree",
+  "fahrenheit",
+  "fluid-ounce",
+  "foot",
+  "gallon",
+  "gigabit",
+  "gigabyte",
+  "gram",
+  "hectare",
+  "hour",
+  "inch",
+  "kilobit",
+  "kilobyte",
+  "kilogram",
+  "kilometer",
+  "liter",
+  "megabit",
+  "megabyte",
+  "meter",
+  "microsecond",
+  "mile",
+  "mile-scandinavian",
+  "milliliter",
+  "millimeter",
+  "millisecond",
+  "minute",
+  "month",
+  "nanosecond",
+  "ounce",
+  "percent",
+  "petabyte",
+  "pound",
+  "second",
+  "stone",
+  "terabit",
+  "terabyte",
+  "week",
+  "yard",
+  "year",
+];
+
+function* numberFormatOptions() {
+  const currencyDisplayOptions = ["symbol", "narrowSymbol", "code", "name"];
+  const unitDisplayOptions = ["short", "long", "narrow"];
+
+  for (const locale of LOCALES) {
+    for (const currency of CURRENCIES) {
+      for (const currencyDisplay of currencyDisplayOptions) {
+        yield { locale, style: "currency", currency, currencyDisplay };
+      }
+    }
+    for (const unit of NUMBER_UNITS.slice(0, 20)) {
+      for (const unitDisplay of unitDisplayOptions) {
+        yield { locale, style: "unit", unit, unitDisplay };
+      }
+    }
+    yield { locale, style: "decimal" };
+    yield { locale, style: "percent" };
+  }
+}
+
+function runTest(verbose = false) {
+  let lastResult;
+  let totalLength = 0;
+  const NUMBER_FORMAT_COUNT = 10;
+  let counter = 1;
+  for (const options of shuffleOptions(numberFormatOptions).slice(0, 200)) {
+    const formatter = new Intl.NumberFormat(options.locale, options);
+    if (verbose) {
+      console.log(options.locale, JSON.stringify(options));
+    }
+    for (let i = 0; i < NUMBER_FORMAT_COUNT; i++) {
+      counter += 599;
+      const value = counter % 10_000;
+      lastResult = formatter.format(value);
+      if (verbose) {
+        console.log(value, lastResult);
+      }
+      totalLength += lastResult.length;
+      const formatPartsResult = formatter.formatToParts(value);
+      for (const part of formatPartsResult) {
+        totalLength += part.value.length;
+      }
+    }
+  }
+  return { lastResult, totalLength, expectedMinLength: 40_000 };
+}
diff --git a/intl/src/PluralRules.js b/intl/src/PluralRules.js
new file mode 100644
index 00000000..944aa390
--- /dev/null
+++ b/intl/src/PluralRules.js
@@ -0,0 +1,38 @@
+function* pluralRulesOptions() {
+  const typeOptions = ["cardinal", "ordinal"];
+  for (const locale of LOCALES) {
+    for (const type of typeOptions) {
+      yield { locale, type };
+    }
+  }
+}
+
+function runTest(verbose = false) {
+  let lastResult;
+  let totalLength = 0;
+  const PLURAL_RULES_COUNT = 1000;
+  for (const { locale, type } of shuffleOptions(pluralRulesOptions)) {
+    if (verbose) {
+      console.log(locale, type);
+    }
+    const formatter = new Intl.PluralRules(locale, { type });
+    let i = 0;
+    for (let value = 0; value < 4; value++) {
+      lastResult = formatter.select(value);
+      totalLength += lastResult.length;
+      if (verbose) {
+        console.log(value, lastResult);
+      }
+      i++;
+    }
+    for (; i < PLURAL_RULES_COUNT; i++) {
+      const value = Math.floor(Math.random() * 1000);
+      lastResult = formatter.select(value);
+      totalLength += lastResult.length;
+      if (verbose) {
+        console.log(value, lastResult);
+      }
+    }
+  }
+  return { lastResult, totalLength, expectedMinLength: 244_000 };
+}
diff --git a/intl/src/RelativeTimeFormat.js b/intl/src/RelativeTimeFormat.js
new file mode 100644
index 00000000..e0d0394a
--- /dev/null
+++ b/intl/src/RelativeTimeFormat.js
@@ -0,0 +1,53 @@
+const UNITS = [
+  "year",
+  "quarter",
+  "month",
+  "week",
+  "day",
+  "hour",
+  "minute",
+  "second",
+];
+
+function* relativeTimeFormatOptions() {
+  const styleOptions = ["long", "short", "narrow"];
+  const numericOptions = ["always", "auto"];
+  for (const locale of LOCALES) {
+    for (const style of styleOptions) {
+      for (const numeric of numericOptions) {
+        yield { locale, style, numeric };
+      }
+    }
+  }
+}
+
+function runTest(verbose = false) {
+  let lastResult;
+  let totalLength = 0;
+  const RELATIVE_TIME_FORMAT_COUNT = 100;
+  let unitIndex = 0;
+  for (const { locale, style, numeric } of shuffleOptions(
+    relativeTimeFormatOptions
+  )) {
+    const options = { style, numeric };
+    if (verbose) {
+      console.log(locale, JSON.stringify(options));
+    }
+    const formatter = new Intl.RelativeTimeFormat(locale, options);
+    for (let i = 0; i < RELATIVE_TIME_FORMAT_COUNT; i++) {
+      const unit = UNITS[unitIndex % UNITS.length];
+      unitIndex++;
+      const value = Math.random() * 100 - 50;
+      lastResult = formatter.format(value, unit);
+      if (verbose) {
+        console.log(value, unit, lastResult);
+      }
+      totalLength += lastResult.length;
+      const formatPartsResult = formatter.formatToParts(value, unit);
+      for (const part of formatPartsResult) {
+        totalLength += part.value.length;
+      }
+    }
+  }
+  return { lastResult, totalLength, expectedMinLength: 432_000 };
+}
diff --git a/intl/src/helper.js b/intl/src/helper.js
new file mode 100644
index 00000000..9a173f68
--- /dev/null
+++ b/intl/src/helper.js
@@ -0,0 +1,39 @@
+function shuffleOptions(optionsGenerator) {
+  const options = Array.from(optionsGenerator());
+  for (let i = options.length - 1; i > 0; i--) {
+    const j = Math.floor(Math.random() * (i + 1));
+    [options[i], options[j]] = [options[j], options[i]];
+  }
+  return options;
+}
+
+const LOCALES = [
+  "ar-SA",
+  "zh-CN",
+  "zh-TW",
+  "da-DK",
+  "en-US",
+  "en-GB",
+  "en-CA",
+  "en-AU",
+  "fr-FR",
+  "fr-CA",
+  "de-DE",
+  "hi-IN",
+  "it-IT",
+  "ja-JP",
+  "ko-KR",
+  "pt-BR",
+  "pt-PT",
+  "ru-RU",
+  "es-ES",
+  "es-MX",
+  "sw-KE",
+  "sv-SE",
+  "th-TH",
+  "tr-TR",
+  "vi-VN",
+];
+
+globalThis.console ??= {};
+console.log ??= (...args) => print(...args);