diff --git a/src/wp-includes/vars.php b/src/wp-includes/vars.php
index d6160dd23e..dc28b8509a 100644
--- a/src/wp-includes/vars.php
+++ b/src/wp-includes/vars.php
@@ -144,11 +144,16 @@ $is_iis7 = $is_IIS && (int) substr( $_SERVER['SERVER_SOFTWARE'], strpos( $_SERVE
  * Test if the current browser runs on a mobile device (smart phone, tablet, etc.)
  *
  * @since 3.4.0
+ * @since 6.4.0 Added checking for the Sec-CH-UA-Mobile request header.
  *
  * @return bool
  */
 function wp_is_mobile() {
-	if ( empty( $_SERVER['HTTP_USER_AGENT'] ) ) {
+	if ( isset( $_SERVER['HTTP_SEC_CH_UA_MOBILE'] ) ) {
+		// This is the `Sec-CH-UA-Mobile` user agent client hint HTTP request header.
+		// See <https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Sec-CH-UA-Mobile>.
+		$is_mobile = ( '?1' === $_SERVER['HTTP_SEC_CH_UA_MOBILE'] );
+	} elseif ( empty( $_SERVER['HTTP_USER_AGENT'] ) ) {
 		$is_mobile = false;
 	} elseif ( str_contains( $_SERVER['HTTP_USER_AGENT'], 'Mobile' ) // Many mobile devices (all iPhone, iPad, etc.)
 		|| str_contains( $_SERVER['HTTP_USER_AGENT'], 'Android' )
diff --git a/tests/phpunit/tests/vars.php b/tests/phpunit/tests/vars.php
new file mode 100644
index 0000000000..ceb0a69c7c
--- /dev/null
+++ b/tests/phpunit/tests/vars.php
@@ -0,0 +1,147 @@
+<?php
+/**
+ * Test functions in wp-includes/vars.php
+ *
+ * @group vars.php
+ */
+class Tests_Vars extends WP_UnitTestCase {
+
+	/**
+	 * Backup of $_SERVER.
+	 *
+	 * @var array
+	 */
+	protected $server_vars = array();
+
+	/**
+	 * Set up.
+	 */
+	public function set_up() {
+		$this->server_vars = $_SERVER;
+		parent::set_up();
+	}
+
+	/**
+	 * Tear down.
+	 */
+	public function tear_down() {
+		$_SERVER = $this->server_vars;
+		parent::tear_down();
+	}
+
+	/**
+	 * Data provider to test wp_is_mobile().
+	 *
+	 * @return array
+	 */
+	function get_data_to_test_wp_is_mobile(): array {
+		return array(
+			'mobile client hint'  => array(
+				'headers'  => array(
+					'HTTP_SEC_CH_UA_MOBILE' => '?1',
+				),
+				'expected' => true,
+			),
+			'desktop client hint' => array(
+				'headers'  => array(
+					'HTTP_SEC_CH_UA_MOBILE' => '?0',
+				),
+				'expected' => false,
+			),
+			'no user agent'       => array(
+				'headers'  => array(),
+				'expected' => false,
+			),
+			'desktop safari'      => array(
+				'headers'  => array(
+					'HTTP_USER_AGENT' => 'Mozilla/5.0 (Macintosh; Intel Mac OS X 13_5_2) AppleWebKit/605.1.15 (KHTML, like Gecko) Version/16.5 Safari/605.1.15',
+				),
+				'expected' => false,
+			),
+			'mobile safari'       => array(
+				'headers'  => array(
+					'HTTP_USER_AGENT' => 'Mozilla/5.0 (iPhone; CPU iPhone OS 16_6_1 like Mac OS X) AppleWebKit/605.1.15 (KHTML, like Gecko) Version/16.5 Mobile/15E148 Safari/604.1',
+				),
+				'expected' => true,
+			),
+			'mobile android'      => array(
+				'headers'  => array(
+					'HTTP_USER_AGENT' => 'Mozilla/5.0 (Linux; Android 10) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/117.0.5938.60 Mobile Safari/537.36',
+				),
+				'expected' => true,
+			),
+			'silk'                => array(
+				'headers'  => array(
+					'HTTP_USER_AGENT' => 'Mozilla/5.0 (Linux; U; Android 4.4.3; KFTHWI Build/KTU84M) AppleWebKit/537.36 (KHTML, like Gecko) Silk/44.1.54 like Chrome/44.0.2403.63 Mobile Safari/537.36',
+				),
+				'expected' => true,
+			),
+			'kindle'              => array(
+				'headers'  => array(
+					'HTTP_USER_AGENT' => 'Mozilla/4.0 (compatible; Linux 2.6.10) NetFront/3.3 Kindle/1.0 (screen 600x800)',
+				),
+				'expected' => true,
+			),
+			'blackberry'          => array(
+				'headers'  => array(
+					'HTTP_USER_AGENT' => 'Mozilla/5.0 (Linux; Android 8.1.0; BlackBerry BBB100-4 Build/OPM1.171019.026) IPTV Pro/7.0.6',
+				),
+				'expected' => true,
+			),
+			'opera mini'          => array(
+				'headers'  => array(
+					'HTTP_USER_AGENT' => 'Opera/9.80 (Android; Opera Mini/69.0.2254/191.303; U; en) Presto/2.12.423 Version/12.16',
+				),
+				'expected' => true,
+			),
+			'opera mobi'          => array(
+				'headers'  => array(
+					'HTTP_USER_AGENT' => 'Opera/9.80 (Linux i686; Opera Mobi/1038; U; en) Presto/2.5.24 Version/10.00',
+				),
+				'expected' => true,
+			),
+		);
+	}
+
+	/**
+	 * Tests that wp_is_mobile() .
+	 *
+	 * @ticket 59370
+	 *
+	 * @covers ::wp_is_mobile
+	 *
+	 * @dataProvider get_data_to_test_wp_is_mobile
+	 *
+	 * @param array $headers  Headers in $_SERVER.
+	 * @param bool  $expected Whether expected.
+	 */
+	function test_wp_is_mobile( array $headers, bool $expected ) {
+		foreach ( $headers as $key => $value ) {
+			$_SERVER[ $key ] = $value;
+		}
+		$this->assertSame( $expected, wp_is_mobile() );
+	}
+
+	/**
+	 * Tests that filter can override output of wp_is_mobile() to be true.
+	 *
+	 * @covers ::wp_is_mobile
+	 */
+	function test_wp_is_mobile_is_true_with_filter() {
+		$this->assertFalse( wp_is_mobile() );
+		add_filter( 'wp_is_mobile', '__return_true' );
+		$this->assertTrue( wp_is_mobile() );
+	}
+
+	/**
+	 * Tests that filter can override output of wp_is_mobile() to be false.
+	 *
+	 * @covers ::wp_is_mobile
+	 */
+	function test_wp_is_mobile_is_false_with_filter() {
+		$_SERVER['HTTP_USER_AGENT'] = 'Mozilla/5.0 (Linux; Android 10) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/117.0.5938.60 Mobile Safari/537.36';
+		$this->assertTrue( wp_is_mobile() );
+		add_filter( 'wp_is_mobile', '__return_false' );
+		$this->assertFalse( wp_is_mobile() );
+	}
+}