diff --git a/.circleci/config.yml b/.circleci/config.yml
index c4feb48379..eac7fa38be 100644
--- a/.circleci/config.yml
+++ b/.circleci/config.yml
@@ -313,7 +313,7 @@ jobs:
 
   lint:
     docker:
-      - image: cimg/php:8.1.27-node
+      - image: cimg/php:8.3-node
     steps:
       - checkout
       - run:
diff --git a/README.md b/README.md
index c20e8dfee5..3e04bcceba 100644
--- a/README.md
+++ b/README.md
@@ -243,15 +243,17 @@ PHPCodesniffer and the parallel linting tools should be installed automatically
 The following composer scripts are aliases for running these tools.
 
 * Check for code style errors across all project files. Must have zero errors:
-  `./bin/composer phpcs-errors`:
-* Check for code style errors and warnings across all project files.
-  `./bin/composer phpcs-strict`
+`./bin/composer phpcs-errors`
+* Check for code style errors and warnings across all project file
+`./bin/composer phpcs-strict`
 * Check for code style errors in current branch. Must have zero errors:
   `./bin/composer phpcs-changes`
 * Check for code style errors and warnings in current branch.
   `./bin/composer phpcs-changes-strict`
 * Check for PHP lint errors
   `./bin/composer php-lint`
+* Check for PHP 8.3 compatibility
+  `./bin/composer php-compatibility`
 
 ## Checking code with PHPStan
 
diff --git a/composer.json b/composer.json
index b62da6a19f..c180dcc0f8 100644
--- a/composer.json
+++ b/composer.json
@@ -170,8 +170,10 @@
         "drupal/coder": "^8.3",
         "mglaman/phpstan-drupal": "*",
         "php-parallel-lint/php-parallel-lint": "^1.4",
+        "phpcompatibility/php-compatibility": "^9.3",
         "phpstan/phpstan": "*",
-        "phpstan/phpstan-deprecation-rules": "*"
+        "phpstan/phpstan-deprecation-rules": "*",
+        "rector/rector": "^2.0"
     },
     "scripts": {
         "changed-files": [
@@ -194,6 +196,9 @@
         ],
         "phpstan": [
             "vendor/bin/phpstan --memory-limit=1G"
+        ],
+        "php-compatibility": [
+            "vendor/bin/phpcs -pn --runtime-set testVersion 8.3- web/modules/custom web/themes/custom -d memory_limit=2G --standard=.phpcs.xml.dist"
         ]
     }
 }
diff --git a/composer.lock b/composer.lock
index 3059fc325a..fd4fb724d9 100644
--- a/composer.lock
+++ b/composer.lock
@@ -4,7 +4,7 @@
         "Read more about it at https://getcomposer.org/doc/01-basic-usage.md#installing-dependencies",
         "This file is @generated automatically"
     ],
-    "content-hash": "890b214b364740bcff34f40f82c6b50b",
+    "content-hash": "8f5ea57e015cebf68b6fb36a9d214f05",
     "packages": [
         {
             "name": "asm89/stack-cors",
@@ -8222,16 +8222,16 @@
         },
         {
             "name": "phpoffice/phpspreadsheet",
-            "version": "2.3.3",
+            "version": "2.3.5",
             "source": {
                 "type": "git",
                 "url": "https://github.com/PHPOffice/PhpSpreadsheet.git",
-                "reference": "91a4b42e41976a0b2f839720c3e20a12a84f6852"
+                "reference": "d836f2d7308a192441ccd1546545890b378af913"
             },
             "dist": {
                 "type": "zip",
-                "url": "https://api.github.com/repos/PHPOffice/PhpSpreadsheet/zipball/91a4b42e41976a0b2f839720c3e20a12a84f6852",
-                "reference": "91a4b42e41976a0b2f839720c3e20a12a84f6852",
+                "url": "https://api.github.com/repos/PHPOffice/PhpSpreadsheet/zipball/d836f2d7308a192441ccd1546545890b378af913",
+                "reference": "d836f2d7308a192441ccd1546545890b378af913",
                 "shasum": ""
             },
             "require": {
@@ -8320,9 +8320,9 @@
             ],
             "support": {
                 "issues": "https://github.com/PHPOffice/PhpSpreadsheet/issues",
-                "source": "https://github.com/PHPOffice/PhpSpreadsheet/tree/2.3.3"
+                "source": "https://github.com/PHPOffice/PhpSpreadsheet/tree/2.3.5"
             },
-            "time": "2024-11-22T06:11:37+00:00"
+            "time": "2024-12-27T05:17:46+00:00"
         },
         {
             "name": "phpowermove/docblock",
@@ -12268,6 +12268,68 @@
             },
             "time": "2024-03-27T12:14:49+00:00"
         },
+        {
+            "name": "phpcompatibility/php-compatibility",
+            "version": "9.3.5",
+            "source": {
+                "type": "git",
+                "url": "https://github.com/PHPCompatibility/PHPCompatibility.git",
+                "reference": "9fb324479acf6f39452e0655d2429cc0d3914243"
+            },
+            "dist": {
+                "type": "zip",
+                "url": "https://api.github.com/repos/PHPCompatibility/PHPCompatibility/zipball/9fb324479acf6f39452e0655d2429cc0d3914243",
+                "reference": "9fb324479acf6f39452e0655d2429cc0d3914243",
+                "shasum": ""
+            },
+            "require": {
+                "php": ">=5.3",
+                "squizlabs/php_codesniffer": "^2.3 || ^3.0.2"
+            },
+            "conflict": {
+                "squizlabs/php_codesniffer": "2.6.2"
+            },
+            "require-dev": {
+                "phpunit/phpunit": "~4.5 || ^5.0 || ^6.0 || ^7.0"
+            },
+            "suggest": {
+                "dealerdirect/phpcodesniffer-composer-installer": "^0.5 || This Composer plugin will sort out the PHPCS 'installed_paths' automatically.",
+                "roave/security-advisories": "dev-master || Helps prevent installing dependencies with known security issues."
+            },
+            "type": "phpcodesniffer-standard",
+            "notification-url": "https://packagist.org/downloads/",
+            "license": [
+                "LGPL-3.0-or-later"
+            ],
+            "authors": [
+                {
+                    "name": "Wim Godden",
+                    "homepage": "https://github.com/wimg",
+                    "role": "lead"
+                },
+                {
+                    "name": "Juliette Reinders Folmer",
+                    "homepage": "https://github.com/jrfnl",
+                    "role": "lead"
+                },
+                {
+                    "name": "Contributors",
+                    "homepage": "https://github.com/PHPCompatibility/PHPCompatibility/graphs/contributors"
+                }
+            ],
+            "description": "A set of sniffs for PHP_CodeSniffer that checks for PHP cross-version compatibility.",
+            "homepage": "http://techblog.wimgodden.be/tag/codesniffer/",
+            "keywords": [
+                "compatibility",
+                "phpcs",
+                "standards"
+            ],
+            "support": {
+                "issues": "https://github.com/PHPCompatibility/PHPCompatibility/issues",
+                "source": "https://github.com/PHPCompatibility/PHPCompatibility"
+            },
+            "time": "2019-12-27T09:44:58+00:00"
+        },
         {
             "name": "phpstan/phpdoc-parser",
             "version": "1.33.0",
@@ -12420,6 +12482,65 @@
             },
             "time": "2024-11-28T21:56:36+00:00"
         },
+        {
+            "name": "rector/rector",
+            "version": "2.0.4",
+            "source": {
+                "type": "git",
+                "url": "https://github.com/rectorphp/rector.git",
+                "reference": "df5de7b80deced1ea7f719a0b4d02e4aee87dd21"
+            },
+            "dist": {
+                "type": "zip",
+                "url": "https://api.github.com/repos/rectorphp/rector/zipball/df5de7b80deced1ea7f719a0b4d02e4aee87dd21",
+                "reference": "df5de7b80deced1ea7f719a0b4d02e4aee87dd21",
+                "shasum": ""
+            },
+            "require": {
+                "php": "^7.4|^8.0",
+                "phpstan/phpstan": "^2.0.4"
+            },
+            "conflict": {
+                "rector/rector-doctrine": "*",
+                "rector/rector-downgrade-php": "*",
+                "rector/rector-phpunit": "*",
+                "rector/rector-symfony": "*"
+            },
+            "suggest": {
+                "ext-dom": "To manipulate phpunit.xml via the custom-rule command"
+            },
+            "bin": [
+                "bin/rector"
+            ],
+            "type": "library",
+            "autoload": {
+                "files": [
+                    "bootstrap.php"
+                ]
+            },
+            "notification-url": "https://packagist.org/downloads/",
+            "license": [
+                "MIT"
+            ],
+            "description": "Instant Upgrade and Automated Refactoring of any PHP code",
+            "keywords": [
+                "automation",
+                "dev",
+                "migration",
+                "refactoring"
+            ],
+            "support": {
+                "issues": "https://github.com/rectorphp/rector/issues",
+                "source": "https://github.com/rectorphp/rector/tree/2.0.4"
+            },
+            "funding": [
+                {
+                    "url": "https://github.com/tomasvotruba",
+                    "type": "github"
+                }
+            ],
+            "time": "2024-12-26T23:06:19+00:00"
+        },
         {
             "name": "sirbrillig/phpcs-variable-analysis",
             "version": "v2.11.22",
diff --git a/rector.php b/rector.php
new file mode 100644
index 0000000000..6158933cfd
--- /dev/null
+++ b/rector.php
@@ -0,0 +1,18 @@
+<?php
+
+declare(strict_types=1);
+
+use Rector\Config\RectorConfig;
+use Rector\Set\ValueObject\SetList;
+
+return static function (RectorConfig $rectorConfig): void {
+  $rectorConfig->paths([
+    __DIR__ . '/web/modules/custom/',
+    __DIR__ . '/web/themes/custom/',
+  ]);
+
+  // Other configurations, such as rule sets
+  $rectorConfig->sets([
+    SetList::PHP_83,
+  ]);
+};
diff --git a/web/modules/custom/usa_orphaned_entities/src/Form/OrphanedEntitiesSettings.php b/web/modules/custom/usa_orphaned_entities/src/Form/OrphanedEntitiesSettings.php
index b65e7cb2d2..8d46775316 100644
--- a/web/modules/custom/usa_orphaned_entities/src/Form/OrphanedEntitiesSettings.php
+++ b/web/modules/custom/usa_orphaned_entities/src/Form/OrphanedEntitiesSettings.php
@@ -36,6 +36,7 @@ public function getFormId(): string {
   /**
    * {@inheritdoc}
    */
+  #[\Override]
   public function buildForm(array $form, FormStateInterface $form_state): array {
     $form['#attached']['library'][] = 'usa_orphaned_entities/orphaned';
     $form = parent::buildForm($form, $form_state);
@@ -94,6 +95,7 @@ public function buildForm(array $form, FormStateInterface $form_state): array {
   /**
    * {@inheritdoc}
    */
+  #[\Override]
   public function validateForm(array &$form, FormStateInterface $form_state) {
     // foreach ($form['#entity_reference'] as $index => $entity_reference) {
 
@@ -113,6 +115,7 @@ public function validateForm(array &$form, FormStateInterface $form_state) {
   /**
    * {@inheritdoc}
    */
+  #[\Override]
   public function submitForm(array &$form, FormStateInterface $form_state): void {
     $config = $this->config('orphaned_entities.settings');
     foreach ($form['#entity_reference'] as $index => $entity_reference) {
diff --git a/web/modules/custom/usa_twig_vars/src/TaxonomyDatalayerBuilder.php b/web/modules/custom/usa_twig_vars/src/TaxonomyDatalayerBuilder.php
index 264cb50d86..135edacd6a 100644
--- a/web/modules/custom/usa_twig_vars/src/TaxonomyDatalayerBuilder.php
+++ b/web/modules/custom/usa_twig_vars/src/TaxonomyDatalayerBuilder.php
@@ -18,17 +18,17 @@ class TaxonomyDatalayerBuilder {
   public const HOME_TITLE_ES = "Página principal";
   public const HOME_URL_ES = "/es/";
 
-  private const ABOUT_GOVT_EN = "About the U.S. and its government";
-  private const ABOUT_URL_EN = "/about-the-us";
+  private const string ABOUT_GOVT_EN = "About the U.S. and its government";
+  private const string ABOUT_URL_EN = "/about-the-us";
 
-  private const ABOUT_GOVT_ES = "Acerca de EE. UU. y su Gobierno";
-  private const ABOUT_URL_ES = "/es/acerca-de-estados-unidos";
+  private const string ABOUT_GOVT_ES = "Acerca de EE. UU. y su Gobierno";
+  private const string ABOUT_URL_ES = "/es/acerca-de-estados-unidos";
 
-  private const AGENCY_INDEX_URL_EN = '/agency-index';
-  private const AGENCY_INDEX_URL_ES = '/es/indice-agencias';
+  private const string AGENCY_INDEX_URL_EN = '/agency-index';
+  private const string AGENCY_INDEX_URL_ES = '/es/indice-agencias';
 
-  private const STATE_INDEX_URL_EN = '/state-governments';
-  private const STATE_INDEX_URL_ES = '/es/gobiernos-estatales';
+  private const string STATE_INDEX_URL_EN = '/state-governments';
+  private const string STATE_INDEX_URL_ES = '/es/gobiernos-estatales';
 
   /**
    * Language code for entity.
diff --git a/web/modules/custom/usagov_benefit_finder/src/Form/BenefitFinderSettingsForm.php b/web/modules/custom/usagov_benefit_finder/src/Form/BenefitFinderSettingsForm.php
index 14280934ec..3bd4af1852 100644
--- a/web/modules/custom/usagov_benefit_finder/src/Form/BenefitFinderSettingsForm.php
+++ b/web/modules/custom/usagov_benefit_finder/src/Form/BenefitFinderSettingsForm.php
@@ -17,6 +17,7 @@ public function getFormId() {
   /**
    * {@inheritdoc}
    */
+  #[\Override]
   public function buildForm(array $form, FormStateInterface $form_state) {
     $form = parent::buildForm($form, $form_state);
 
@@ -35,6 +36,7 @@ public function buildForm(array $form, FormStateInterface $form_state) {
   /**
    * {@inheritdoc}
    */
+  #[\Override]
   public function submitForm(array &$form, FormStateInterface $form_state) {
     $this->config('usagov_benefit_finder.settings')
       ->set('automate_json_data_file_generating', $form_state->getValue('automate_json_data_file_generating'))
diff --git a/web/modules/custom/usagov_directories/src/Form/DirectoryRecordsAddAcronymsForm.php b/web/modules/custom/usagov_directories/src/Form/DirectoryRecordsAddAcronymsForm.php
index c74827dec5..dad38164ff 100644
--- a/web/modules/custom/usagov_directories/src/Form/DirectoryRecordsAddAcronymsForm.php
+++ b/web/modules/custom/usagov_directories/src/Form/DirectoryRecordsAddAcronymsForm.php
@@ -59,6 +59,7 @@ public function buildForm(array $form, FormStateInterface $form_state) {
   /**
    * {@inheritdoc}
    */
+  #[\Override]
   public function validateForm(array &$form, FormStateInterface $form_state) {
     $all_files = $this->getRequest()->files->get('files', []);
     $file = $all_files['acronym_file'];
diff --git a/web/modules/custom/usagov_directories/src/Form/DirectoryRecordsAddSynonymsForm.php b/web/modules/custom/usagov_directories/src/Form/DirectoryRecordsAddSynonymsForm.php
index d7c7b260a7..bdd87849c9 100644
--- a/web/modules/custom/usagov_directories/src/Form/DirectoryRecordsAddSynonymsForm.php
+++ b/web/modules/custom/usagov_directories/src/Form/DirectoryRecordsAddSynonymsForm.php
@@ -59,6 +59,7 @@ public function buildForm(array $form, FormStateInterface $form_state) {
   /**
    * {@inheritdoc}
    */
+  #[\Override]
   public function validateForm(array &$form, FormStateInterface $form_state) {
     $all_files = $this->getRequest()->files->get('files', []);
     $file = $all_files['synonym_file'];
diff --git a/web/modules/custom/usagov_directories/src/Form/DirectoryRecordsAddTogglesForm.php b/web/modules/custom/usagov_directories/src/Form/DirectoryRecordsAddTogglesForm.php
index f632367ff6..26512c6cdb 100644
--- a/web/modules/custom/usagov_directories/src/Form/DirectoryRecordsAddTogglesForm.php
+++ b/web/modules/custom/usagov_directories/src/Form/DirectoryRecordsAddTogglesForm.php
@@ -60,6 +60,7 @@ public function buildForm(array $form, FormStateInterface $form_state) {
   /**
    * {@inheritdoc}
    */
+  #[\Override]
   public function validateForm(array &$form, FormStateInterface $form_state) {
     $all_files = $this->getRequest()->files->get('files', []);
     $file = $all_files['toggle_map_file'];
diff --git a/web/modules/custom/usagov_login/src/Form/LoginSettingsForm.php b/web/modules/custom/usagov_login/src/Form/LoginSettingsForm.php
index dc4e6a2636..64405c054e 100755
--- a/web/modules/custom/usagov_login/src/Form/LoginSettingsForm.php
+++ b/web/modules/custom/usagov_login/src/Form/LoginSettingsForm.php
@@ -36,6 +36,7 @@ public function __construct(ConfigFactoryInterface $config_factory, StateInterfa
   /**
    * {@inheritdoc}
    */
+  #[\Override]
   public static function create(ContainerInterface $container) {
     return new static(
       $container->get('config.factory'),
@@ -60,6 +61,7 @@ protected function getEditableConfigNames() {
   /**
    * {@inheritdoc}
    */
+  #[\Override]
   public function buildForm(array $form, FormStateInterface $form_state) {
     $form['sso_login_path'] = [
       '#type' => 'textfield',
@@ -89,6 +91,7 @@ public function buildForm(array $form, FormStateInterface $form_state) {
   /**
    * {@inheritdoc}
    */
+  #[\Override]
   public function submitForm(array &$form, FormStateInterface $form_state) {
 
     $this->state->set('usagov_login_local_form', $form_state->getValue('display_local'));
diff --git a/web/modules/custom/usagov_menus/src/Plugin/Block/SidebarFirstBlock.php b/web/modules/custom/usagov_menus/src/Plugin/Block/SidebarFirstBlock.php
index 1670ca7d5a..e6e8037fac 100644
--- a/web/modules/custom/usagov_menus/src/Plugin/Block/SidebarFirstBlock.php
+++ b/web/modules/custom/usagov_menus/src/Plugin/Block/SidebarFirstBlock.php
@@ -31,10 +31,10 @@
 )]
 class SidebarFirstBlock extends AbstractMenuBlock {
 
-  private const AGENCIES_NID_EN = 629;
-  private const AGENCIES_NID_ES = 1696;
-  private const STATES_NID_EN = 1885;
-  private const STATES_NID_ES = 1870;
+  private const int AGENCIES_NID_EN = 629;
+  private const int AGENCIES_NID_ES = 1696;
+  private const int STATES_NID_EN = 1885;
+  private const int STATES_NID_ES = 1870;
 
   /**
    * {@inheritdoc}