diff --git a/.circleci/config.yml b/.circleci/config.yml
index 0df0750369..16f7be0bba 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 1edf9ff9e4..f19bd742c7 100644
--- a/README.md
+++ b/README.md
@@ -326,24 +326,26 @@ 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`
-* Check for code style errors in current branch. Must have zero errors:
+* 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 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.
+* Check for code style errors and warnings in current branch.  
   `./bin/composer phpcs-changes-strict`
-* Check for PHP lint errors
+* Check for PHP lint errors  
   `./bin/composer php-lint`
+* Check for PHP 8.3 compatibility  
+  `./bin/composer php-compatibility`
 
 ## Project Restart/Reset
+
 Sometimes, Docker problems arise after an upgrade and a more complete restart is needed. After closing down and destroying the existing containers, networks, and volumes the procedure is the same as the full project setup.
 
 
 ### Docker Cleanup
 
-
 ```
 docker compose down
 docker system prune
diff --git a/composer.json b/composer.json
index e16e6a0886..7cbb863e57 100644
--- a/composer.json
+++ b/composer.json
@@ -167,7 +167,9 @@
     },
     "require-dev": {
         "drupal/coder": "^8.3",
-        "php-parallel-lint/php-parallel-lint": "^1.4"
+        "php-parallel-lint/php-parallel-lint": "^1.4",
+        "phpcompatibility/php-compatibility": "^9.3",
+        "rector/rector": "^2.0"
     },
     "scripts": {
         "changed-files": [
@@ -187,6 +189,9 @@
         ],
         "php-lint": [
             "vendor/bin/parallel-lint -e php,module,inc,install,test,profile,theme ./web/modules/custom ./web/themes/custom"
+        ],
+        "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 8cf213b5e2..05488a96a8 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": "750e25aca453a5fccca5ae752bbcd6e3",
+    "content-hash": "5fd38683d9cee7e076430366de6e832a",
     "packages": [
         {
             "name": "asm89/stack-cors",
@@ -11838,6 +11838,68 @@
             },
             "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",
@@ -11885,6 +11947,123 @@
             },
             "time": "2024-10-13T11:25:22+00:00"
         },
+        {
+            "name": "phpstan/phpstan",
+            "version": "2.0.4",
+            "source": {
+                "type": "git",
+                "url": "https://github.com/phpstan/phpstan.git",
+                "reference": "50d276fc3bf1430ec315f2f109bbde2769821524"
+            },
+            "dist": {
+                "type": "zip",
+                "url": "https://api.github.com/repos/phpstan/phpstan/zipball/50d276fc3bf1430ec315f2f109bbde2769821524",
+                "reference": "50d276fc3bf1430ec315f2f109bbde2769821524",
+                "shasum": ""
+            },
+            "require": {
+                "php": "^7.4|^8.0"
+            },
+            "conflict": {
+                "phpstan/phpstan-shim": "*"
+            },
+            "bin": [
+                "phpstan",
+                "phpstan.phar"
+            ],
+            "type": "library",
+            "autoload": {
+                "files": [
+                    "bootstrap.php"
+                ]
+            },
+            "notification-url": "https://packagist.org/downloads/",
+            "license": [
+                "MIT"
+            ],
+            "description": "PHPStan - PHP Static Analysis Tool",
+            "keywords": [
+                "dev",
+                "static analysis"
+            ],
+            "support": {
+                "docs": "https://phpstan.org/user-guide/getting-started",
+                "forum": "https://github.com/phpstan/phpstan/discussions",
+                "issues": "https://github.com/phpstan/phpstan/issues",
+                "security": "https://github.com/phpstan/phpstan/security/policy",
+                "source": "https://github.com/phpstan/phpstan-src"
+            },
+            "funding": [
+                {
+                    "url": "https://github.com/ondrejmirtes",
+                    "type": "github"
+                },
+                {
+                    "url": "https://github.com/phpstan",
+                    "type": "github"
+                }
+            ],
+            "time": "2024-12-17T17:14:01+00:00"
+        },
+        {
+            "name": "rector/rector",
+            "version": "2.0.3",
+            "source": {
+                "type": "git",
+                "url": "https://github.com/rectorphp/rector.git",
+                "reference": "3f27091368bd935dbbaa8387099792fb20f65f68"
+            },
+            "dist": {
+                "type": "zip",
+                "url": "https://api.github.com/repos/rectorphp/rector/zipball/3f27091368bd935dbbaa8387099792fb20f65f68",
+                "reference": "3f27091368bd935dbbaa8387099792fb20f65f68",
+                "shasum": ""
+            },
+            "require": {
+                "php": "^7.4|^8.0",
+                "phpstan/phpstan": "^2.0.1"
+            },
+            "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/2.0.3"
+            },
+            "funding": [
+                {
+                    "url": "https://github.com/tomasvotruba",
+                    "type": "github"
+                }
+            ],
+            "time": "2024-12-12T15:22:19+00:00"
+        },
         {
             "name": "sirbrillig/phpcs-variable-analysis",
             "version": "v2.11.21",
@@ -12102,7 +12281,7 @@
     },
     "prefer-stable": true,
     "prefer-lowest": false,
-    "platform": [],
-    "platform-dev": [],
-    "plugin-api-version": "2.2.0"
+    "platform": {},
+    "platform-dev": {},
+    "plugin-api-version": "2.6.0"
 }
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 9283daafa4..3f2d14d35b 100644
--- a/web/modules/custom/usa_orphaned_entities/src/Form/OrphanedEntitiesSettings.php
+++ b/web/modules/custom/usa_orphaned_entities/src/Form/OrphanedEntitiesSettings.php
@@ -17,6 +17,7 @@ public function getFormId() {
   /**
    * {@inheritdoc}
    */
+  #[\Override]
   public function buildForm(array $form, FormStateInterface $form_state) {
     $entityTypeManager = \Drupal::service('entity_type.manager');
 
@@ -77,6 +78,7 @@ public function buildForm(array $form, FormStateInterface $form_state) {
   /**
    * {@inheritdoc}
    */
+  #[\Override]
   public function validateForm(array &$form, FormStateInterface $form_state) {
     // foreach ($form['entity_reference'] as $index => $entity_reference) {
 
@@ -96,6 +98,7 @@ public function validateForm(array &$form, FormStateInterface $form_state) {
   /**
    * {@inheritdoc}
    */
+  #[\Override]
   public function submitForm(array &$form, FormStateInterface $form_state) {
     $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 45f36e110a..ce7ee9b502 100644
--- a/web/modules/custom/usagov_directories/src/Form/DirectoryRecordsAddAcronymsForm.php
+++ b/web/modules/custom/usagov_directories/src/Form/DirectoryRecordsAddAcronymsForm.php
@@ -48,6 +48,7 @@ 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 e438bdee98..0a465ecdf8 100644
--- a/web/modules/custom/usagov_directories/src/Form/DirectoryRecordsAddSynonymsForm.php
+++ b/web/modules/custom/usagov_directories/src/Form/DirectoryRecordsAddSynonymsForm.php
@@ -48,6 +48,7 @@ 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 f12d6d79d9..6950753115 100644
--- a/web/modules/custom/usagov_directories/src/Form/DirectoryRecordsAddTogglesForm.php
+++ b/web/modules/custom/usagov_directories/src/Form/DirectoryRecordsAddTogglesForm.php
@@ -48,6 +48,7 @@ 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 9004c7c25d..61b9355301 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}