diff --git a/typo3/sysext/core/Classes/Utility/ClientUtility.php b/typo3/sysext/core/Classes/Utility/ClientUtility.php
index 429e65cfbea20f711f6b5c89d3d85d8b0d6350b3..22e2f1d2bcc053be7d00fdaae9158b89bca59fd3 100644
--- a/typo3/sysext/core/Classes/Utility/ClientUtility.php
+++ b/typo3/sysext/core/Classes/Utility/ClientUtility.php
@@ -24,9 +24,11 @@ class ClientUtility
      *
      * @param string $userAgent The useragent string, \TYPO3\CMS\Core\Utility\GeneralUtility::getIndpEnv('HTTP_USER_AGENT')
      * @return array Contains keys "browser", "version", "system
+     * @deprecated
      */
     public static function getBrowserInfo($userAgent)
     {
+        trigger_error('Method getBrowserInfo() is deprecated since v9 and will be removed with v10', E_USER_DEPRECATED);
         // Hook: $TYPO3_CONF_VARS['SC_OPTIONS']['t3lib/div/class.t3lib_utility_client.php']['getBrowserInfo']:
         $getBrowserInfoHooks = &$GLOBALS['TYPO3_CONF_VARS']['SC_OPTIONS']['t3lib/div/class.t3lib_utility_client.php']['getBrowserInfo'];
         if (is_array($getBrowserInfoHooks)) {
@@ -174,9 +176,11 @@ class ClientUtility
      *
      * @param string $version A string with version number, eg. "/7.32 blablabla
      * @return float Returns double value, eg. "7.32
+     * @deprecated
      */
     public static function getVersion($version)
     {
+        trigger_error('Method getVersion() is deprecated since v9 and will be removed with v10', E_USER_DEPRECATED);
         return (float)preg_replace('/^[^0-9]*/', '', $version);
     }
 }
diff --git a/typo3/sysext/core/Documentation/Changelog/master/Deprecation-82903-DeprecateClientUtility.rst b/typo3/sysext/core/Documentation/Changelog/master/Deprecation-82903-DeprecateClientUtility.rst
new file mode 100644
index 0000000000000000000000000000000000000000..3d0e33533891556dd77474fd3377705ea33952c3
--- /dev/null
+++ b/typo3/sysext/core/Documentation/Changelog/master/Deprecation-82903-DeprecateClientUtility.rst
@@ -0,0 +1,36 @@
+.. include:: ../../Includes.txt
+
+=============================================
+Deprecation: #82903 - Deprecate ClientUtility
+=============================================
+
+See :issue:`82903`
+
+Description
+===========
+
+Class :php:`\TYPO3\CMS\Core\Utility\ClientUtility` has been marked as deprecated and should not be
+used any longer.
+
+
+Impact
+======
+
+Using this class will throw a deprecation warning.
+
+
+Affected Installations
+======================
+
+Instances with extensions using the methods of the class:
+
+- :php:`getBrowserInfo`
+- :php:`getVersion`
+
+
+Migration
+=========
+
+Use a 3rd party API like https://github.com/piwik/device-detector
+
+.. index:: FullyScanned
diff --git a/typo3/sysext/core/Tests/Unit/Utility/ClientUtilityTest.php b/typo3/sysext/core/Tests/Unit_Deprecated/Utility/ClientUtilityTest.php
similarity index 100%
rename from typo3/sysext/core/Tests/Unit/Utility/ClientUtilityTest.php
rename to typo3/sysext/core/Tests/Unit_Deprecated/Utility/ClientUtilityTest.php
diff --git a/typo3/sysext/install/Configuration/ExtensionScanner/Php/ClassNameMatcher.php b/typo3/sysext/install/Configuration/ExtensionScanner/Php/ClassNameMatcher.php
index 5b144b73983afc6b48cfe18ce471ba258aad6a7c..f29b2401e96619e04fe2bc0de935fb79e96f242c 100644
--- a/typo3/sysext/install/Configuration/ExtensionScanner/Php/ClassNameMatcher.php
+++ b/typo3/sysext/install/Configuration/ExtensionScanner/Php/ClassNameMatcher.php
@@ -442,6 +442,11 @@ return [
             'Deprecation-82805-RenamedAjaxLoginHandlerPHPClass.rst',
         ],
     ],
+    'TYPO3\CMS\Core\Utility\ClientUtility' => [
+        'restFiles' => [
+            'Deprecation-82903-DeprecateClientUtility.rst',
+        ],
+    ],
 
     // Removed interfaces
     'TYPO3\CMS\Backend\Form\DatabaseFileIconsHookInterface' => [