diff --git a/phpstan.neon b/phpstan.neon
index 979b34ac5a..2b087e5511 100644
--- a/phpstan.neon
+++ b/phpstan.neon
@@ -14,8 +14,8 @@ parameters:
     - vendor/php-stubs/wordpress-tests-stubs/wordpress-tests-stubs.php
   type_coverage:
       return_type: 87.6
-      param_type: 79.1
-      property_type: 0 # We can't use typed properties until PHP 7.4 becomes the plugin's minimum version. https://php.watch/versions/7.4/typed-properties
+      param_type: 79
+      property_type: 1.4
       constant_type: 0 # We can't use typed constants until PHP 8.3 becomes the plugin's minimum version. https://php.watch/versions/8.3/typed-constants
       print_suggestions: false
   typeAliases:
diff --git a/src/UI/class-settings-page.php b/src/UI/class-settings-page.php
index 315e5ac06f..e0bc14a4b5 100644
--- a/src/UI/class-settings-page.php
+++ b/src/UI/class-settings-page.php
@@ -62,6 +62,7 @@
  *   custom_taxonomy_section?: string,
  *   cats_as_tags?: bool|string,
  *   content_helper: Parsely_Settings_Options_Content_Helper,
+ *   headline_testing?: Parsely_Options_Headline_Testing,
  *   lowercase_tags?: bool,
  *   force_https_canonicals?: bool,
  *   disable_autotrack?: bool|string,
@@ -81,6 +82,7 @@
  * }
  *
  * @phpstan-import-type Parsely_Options from Parsely
+ * @phpstan-import-type Parsely_Options_Headline_Testing from Parsely
  */
 final class Settings_Page {
 	/**
@@ -262,6 +264,7 @@ public function initialize_settings(): void {
 
 		$this->initialize_basic_section();
 		$this->initialize_content_helper_section();
+		$this->initialize_headline_testing_section();
 		$this->initialize_recrawl_section();
 		$this->initialize_advanced_section();
 	}
@@ -430,7 +433,7 @@ private function initialize_basic_section(): void {
 	}
 
 	/**
-	 * Registers the Content Intelligence section and its settings.
+	 * Registers section and settings for Content Intelligence section.
 	 *
 	 * @since 3.16.0
 	 */
@@ -528,6 +531,138 @@ private function initialize_content_helper_section(): void {
 		);
 	}
 
+	/**
+	 * Registers section and settings for Headline Testing section.
+	 *
+	 * @since 3.21.0
+	 */
+	private function initialize_headline_testing_section(): void {
+		$section_key = 'headline-testing-section';
+
+		add_settings_section(
+			$section_key,
+			__( 'Headline Testing', 'wp-parsely' ),
+			function (): void {
+				echo '<p>' . esc_html__( 'Configure Parse.ly Headline Testing to automatically test different headline variations and optimize for engagement.', 'wp-parsely' ) . '</p>';
+				echo '<p><a href="https://docs.parse.ly/install-headline-testing/" target="_blank" rel="noopener noreferrer">' . esc_html__( 'Learn more about Headline Testing', 'wp-parsely' ) . '</a></p>';
+			},
+			Parsely::MENU_SLUG
+		);
+
+		// Enable Headline Testing.
+		$field_id   = 'headline_testing[enabled]';
+		$field_args = array(
+			'option_key'   => $field_id,
+			'label_for'    => $field_id,
+			'yes_text'     => __( 'Enabled', 'wp-parsely' ),
+			'add_fieldset' => true,
+			'legend'       => __( 'Headline Testing', 'wp-parsely' ),
+			'help_text'    => __( 'Enable Parse.ly Headline Testing to automatically test different headline variations.', 'wp-parsely' ),
+		);
+		add_settings_field(
+			$field_id,
+			__( 'Headline Testing', 'wp-parsely' ),
+			array( $this, 'print_checkbox_tag' ),
+			Parsely::MENU_SLUG,
+			$section_key,
+			$field_args
+		);
+
+		// Installation Method.
+		$field_id   = 'headline_testing[installation_method]';
+		$field_args = array(
+			'option_key'    => $field_id,
+			'label_for'     => $field_id,
+			'help_text'     => __( 'Choose how you want to install the Headline Testing script. One-line snippet is recommended for most sites.', 'wp-parsely' ),
+			'radio_options' => array(
+				'one_line' => __( 'One-line Snippet (Recommended)', 'wp-parsely' ),
+				'advanced' => __( 'Advanced Installation', 'wp-parsely' ),
+			),
+		);
+		add_settings_field(
+			$field_id,
+			__( 'Installation Method', 'wp-parsely' ),
+			array( $this, 'print_radio_tags' ),
+			Parsely::MENU_SLUG,
+			$section_key,
+			$field_args
+		);
+
+		// Enable Flicker Control (Advanced only).
+		$field_id   = 'headline_testing[enable_flicker_control]';
+		$field_args = array(
+			'option_key' => $field_id,
+			'label_for'  => $field_id,
+			'yes_text'   => __( 'Enabled', 'wp-parsely' ),
+			'help_text'  => __( 'Hide page body for up to 500ms to prevent flickering when headlines are replaced. Only available with Advanced installation.', 'wp-parsely' ),
+		);
+		add_settings_field(
+			$field_id,
+			__( 'Enable Flicker Control', 'wp-parsely' ),
+			array( $this, 'print_checkbox_tag' ),
+			Parsely::MENU_SLUG,
+			$section_key,
+			$field_args
+		);
+
+		// Enable Live Updates.
+		$field_id   = 'headline_testing[enable_live_updates]';
+		$field_args = array(
+			'option_key' => $field_id,
+			'label_for'  => $field_id,
+			'yes_text'   => __( 'Enabled', 'wp-parsely' ),
+			'help_text'  => __( 'Watch for new content and automatically update headlines for newly added anchors.', 'wp-parsely' ),
+		);
+		add_settings_field(
+			$field_id,
+			__( 'Enable Live Updates', 'wp-parsely' ),
+			array( $this, 'print_checkbox_tag' ),
+			Parsely::MENU_SLUG,
+			$section_key,
+			$field_args
+		);
+
+		// Live Update Timeout.
+		$field_id   = 'headline_testing[live_update_timeout]';
+		$field_args = array(
+			'option_key'    => $field_id,
+			'label_for'     => $field_id,
+			'help_text'     => __( 'How long to watch for new content (in milliseconds). Default: 30000 (30 seconds).', 'wp-parsely' ),
+			'optional_args' => array(
+				'type'        => 'number',
+				'placeholder' => '30000',
+				'min'         => '1000',
+				'max'         => '60000',
+				'step'        => '1000',
+			),
+		);
+		add_settings_field(
+			$field_id,
+			__( 'Live Update Timeout (ms)', 'wp-parsely' ),
+			array( $this, 'print_text_tag' ),
+			Parsely::MENU_SLUG,
+			$section_key,
+			$field_args
+		);
+
+		// Allow After Content Load.
+		$field_id   = 'headline_testing[allow_after_content_load]';
+		$field_args = array(
+			'option_key' => $field_id,
+			'label_for'  => $field_id,
+			'yes_text'   => __( 'Enabled', 'wp-parsely' ),
+			'help_text'  => __( 'Allow headline swapping even after the main content has loaded. May cause flickering. Highly recommended if you are loading your script asynchronously.', 'wp-parsely' ),
+		);
+		add_settings_field(
+			$field_id,
+			__( 'Allow After Content Load', 'wp-parsely' ),
+			array( $this, 'print_checkbox_tag' ),
+			Parsely::MENU_SLUG,
+			$section_key,
+			$field_args
+		);
+	}
+
 	/**
 	 * Registers section and settings for Recrawl section.
 	 *
@@ -836,25 +971,25 @@ private function print_description_text( $args ): void {
 	 * @param Setting_Arguments $args The arguments for text tag.
 	 */
 	public function print_text_tag( $args ): void {
-		$options = $this->parsely->get_options();
-		$name    = $args['option_key'];
-		/**
-		 * Variable.
-		 *
-		 * @var string
-		 */
-		$value               = $options[ $name ] ?? '';
+		$options             = $this->parsely->get_options();
+		$name                = $args['option_key'];
+		$raw_value           = $this->get_option_value( $name, $options );
+		$value_as_string     = is_scalar( $raw_value ) ? (string) $raw_value : '';
 		$optional_args       = $args['optional_args'] ?? array();
 		$id                  = esc_attr( $name );
-		$name                = Parsely::OPTIONS_KEY . "[$id]";
+		$html_name           = $this->get_html_name_attribute( $name );
 		$is_obfuscated_value = $optional_args['is_obfuscated_value'] ?? false;
-		$value               = $is_obfuscated_value ? $this->get_obfuscated_value( $value ) : esc_attr( $value );
-		$accepted_args       = array( 'placeholder', 'required', 'disabled' );
+		$value               = $is_obfuscated_value ? $this->get_obfuscated_value( $value_as_string ) : esc_attr( $value_as_string );
 		$type                = $optional_args['type'] ?? 'text';
+		$accepted_args       = array( 'placeholder', 'required', 'disabled' );
+
+		if ( 'number' === $type ) {
+			$accepted_args = array_merge( $accepted_args, array( 'min', 'max', 'step' ) );
+		}
 
 		$is_managed = key_exists( $id, $this->parsely->managed_options );
 		echo '<fieldset', $is_managed ? ' disabled>' : '>';
-		printf( "<input type='%s' name='%s' id='%s' value='%s'", esc_attr( $type ), esc_attr( $name ), esc_attr( $id ), esc_attr( $value ) );
+		printf( "<input type='%s' name='%s' id='%s' value='%s'", esc_attr( $type ), esc_attr( $html_name ), esc_attr( $id ), esc_attr( $value ) );
 
 		if ( isset( $args['help_text'] ) ) {
 			echo ' aria-describedby="' . esc_attr( $id ) . '-description"';
@@ -892,19 +1027,9 @@ public function print_checkbox_tag( $args, $options = null ): void {
 		$name         = $args['option_key'];
 		$has_fieldset = isset( $args['add_fieldset'] ) && true === $args['add_fieldset'];
 		$html_id      = rtrim( str_replace( array( '[', ']', '__' ), '_', $name ), '_' );
-		$html_name    = str_replace(
-			'content_helper',
-			'[content_helper]',
-			Parsely::OPTIONS_KEY . esc_attr( $name )
-		);
+		$html_name    = $this->get_html_name_attribute( $name );
 		$yes_text     = $args['yes_text'] ?? '';
-
-		// Get option value.
-		if ( false === strpos( $name, '[' ) ) {
-			$value = $options[ $name ];
-		} else {
-			$value = Parsely::get_nested_option_value( $name, $options );
-		}
+		$value        = $this->get_option_value( $name, $options );
 
 		// Fieldset start.
 		if ( $has_fieldset ) {
@@ -1039,9 +1164,11 @@ public function print_select_tag( $args ): void {
 	 * @param Setting_Arguments $args The arguments for the radio buttons.
 	 */
 	public function print_radio_tags( $args ): void {
+		$options       = $this->parsely->get_options();
 		$name          = $args['option_key'];
 		$id            = esc_attr( $name );
-		$selected      = $this->parsely->get_options()[ $name ];
+		$selected      = $this->get_option_value( $name, $options );
+		$html_name     = $this->get_html_name_attribute( $name );
 		$title         = $args['title'] ?? '';
 		$radio_options = $args['radio_options'] ?? array();
 
@@ -1059,7 +1186,7 @@ public function print_radio_tags( $args ): void {
 				<label for="<?php echo esc_attr( "{$id}_{$value}" ); ?>">
 					<input
 						type="radio"
-						name="<?php echo esc_attr( Parsely::OPTIONS_KEY . "[$id]" ); ?>"
+						name="<?php echo esc_attr( $html_name ); ?>"
 						id="<?php echo esc_attr( "{$id}_{$value}" ); ?>"
 						value="<?php echo esc_attr( $value ); ?>"
 					<?php checked( $selected, $value ); ?>
@@ -1106,6 +1233,53 @@ public function print_media_single_image( $args ): void {
 		$this->print_description_text( $args );
 	}
 
+	/**
+	 * Generates the HTML name attribute for a form field.
+	 *
+	 * Handles nested options (content_helper, headline_testing) and regular
+	 * options, properly escaping and formatting the attribute value.
+	 *
+	 * @since 3.21.0
+	 *
+	 * @param string $name The option key/name.
+	 * @return string The properly formatted and escaped HTML name attribute value.
+	 */
+	private function get_html_name_attribute( string $name ): string {
+		if ( strpos( $name, 'content_helper' ) === 0 ) {
+			return Parsely::OPTIONS_KEY . str_replace(
+				'content_helper',
+				'[content_helper]',
+				esc_attr( $name )
+			);
+		} elseif ( strpos( $name, 'headline_testing' ) === 0 ) {
+			return Parsely::OPTIONS_KEY . str_replace(
+				'headline_testing',
+				'[headline_testing]',
+				esc_attr( $name )
+			);
+		} else {
+			return Parsely::OPTIONS_KEY . '[' . esc_attr( $name ) . ']';
+		}
+	}
+
+	/**
+	 * Gets the value of an option, handling both flat and nested option keys.
+	 *
+	 * @since 3.21.0
+	 *
+	 * @param string          $name    The option key name (may contain brackets for nested options).
+	 * @param Parsely_Options $options The options array to retrieve from.
+	 * @return mixed The option value, or null if not found.
+	 */
+	private function get_option_value( string $name, $options ) {
+		// Get raw value based on whether it's a nested option or not.
+		if ( false === strpos( $name, '[' ) ) {
+			return $options[ $name ] ?? null;
+		} else {
+			return Parsely::get_nested_option_value( $name, $options ) ?? null;
+		}
+	}
+
 	/**
 	 * Prints out the post tracking options table.
 	 *
@@ -1205,6 +1379,7 @@ public function get_tracking_values_for_display(): array {
 	public function validate_options( $input ) {
 		$input = $this->validate_basic_section( $input );
 		$input = $this->validate_content_helper_section( $input );
+		$input = $this->validate_headline_testing_section( $input );
 		$input = $this->validate_recrawl_section( $input );
 		$input = $this->validate_advanced_section( $input );
 
@@ -1390,6 +1565,80 @@ private function validate_content_helper_section( $input ) {
 		return $input;
 	}
 
+	/**
+	 * Validates fields of Headline Testing Section.
+	 *
+	 * @since 3.21.0
+	 *
+	 * @param ParselySettingOptions $input Options from the settings page.
+	 * @return ParselySettingOptions Validated inputs.
+	 */
+	private function validate_headline_testing_section( $input ) {
+		/**
+		 * Sanitizes the Headline Testing data.
+		 *
+		 * @since 3.21.0
+		 */
+		$sanitize = function ( $input ) use ( &$sanitize ) {
+			foreach ( $input as $key => $value ) {
+				if ( is_array( $value ) ) {
+					// Recurse for nested arrays.
+					$input[ $key ] = $sanitize( $value );
+				} else {
+					$input[ $key ] = $this->sanitize_headline_testing_field( $key, $value );
+				}
+			}
+
+			return $input;
+		};
+
+		// Initialize headline_testing array if it doesn't exist.
+		if ( ! isset( $input['headline_testing'] ) ) {
+			$input['headline_testing'] = array();
+		}
+
+		// Ensure all required keys exist with defaults.
+		$input['headline_testing'] = array_merge(
+			$this->parsely->get_default_options()['headline_testing'],
+			$input['headline_testing']
+		);
+
+		// Produce the final array.
+		$options = $this->parsely->get_options()['headline_testing'];
+		$merged  = array_merge( $options, $input['headline_testing'] );
+
+		$input['headline_testing'] = $sanitize( $merged );
+
+		return $input;
+	}
+
+	/**
+	 * Sanitizes headline testing field values.
+	 *
+	 * @since 3.21.0
+	 *
+	 * @param string $key The field key.
+	 * @param mixed  $value The field value.
+	 * @return mixed The sanitized value.
+	 */
+	private function sanitize_headline_testing_field( string $key, $value ) {
+		switch ( $key ) {
+			case 'enabled':
+			case 'enable_flicker_control':
+			case 'enable_live_updates':
+			case 'allow_after_content_load':
+				return 'true' === $value || true === $value;
+			case 'installation_method':
+				$valid_methods = array( 'one_line', 'advanced' );
+				return in_array( $value, $valid_methods, true ) ? $value : 'one_line';
+			case 'live_update_timeout':
+				$timeout = intval( is_scalar( $value ) ? (string) $value : '0' );
+				return ( $timeout >= 1000 && $timeout <= 60000 ) ? $timeout : 30000;
+			default:
+				return sanitize_text_field( is_scalar( $value ) ? (string) $value : '' );
+		}
+	}
+
 	/**
 	 * Validates fields of Recrawl Section.
 	 *
diff --git a/src/class-headline-testing.php b/src/class-headline-testing.php
new file mode 100644
index 0000000000..ae38b58139
--- /dev/null
+++ b/src/class-headline-testing.php
@@ -0,0 +1,209 @@
+<?php
+/**
+ * Headline Testing feature class
+ *
+ * @package Parsely
+ * @since   3.21.0
+ */
+
+declare(strict_types=1);
+
+namespace Parsely;
+
+/**
+ * Handles the Headline Testing feature functionality.
+ *
+ * @since 3.21.0
+ *
+ * @phpstan-import-type Parsely_Options_Headline_Testing from Parsely
+ */
+class Headline_Testing {
+	/**
+	 * Instance of Parsely class.
+	 *
+	 * @var Parsely
+	 */
+	protected $parsely;
+
+	/**
+	 * Data attributes to be added to the one-line script tag.
+	 *
+	 * @var array<string>
+	 */
+	private $data_attributes = array();
+
+	/**
+	 * Constructor.
+	 *
+	 * @since 3.21.0
+	 *
+	 * @param Parsely $parsely Instance of Parsely class.
+	 */
+	public function __construct( Parsely $parsely ) {
+		$this->parsely = $parsely;
+	}
+
+	/**
+	 * Registers the Headline Testing feature.
+	 *
+	 * @since 3.21.0
+	 */
+	public function run(): void {
+		if ( false === $this->can_enable_feature() ) {
+			return;
+		}
+
+		add_action( 'wp_enqueue_scripts', array( $this, 'enqueue_headline_testing_script' ) );
+	}
+
+	/**
+	 * Returns whether the Headline Testing feature can be enabled.
+	 *
+	 * @since 3.21.0
+	 *
+	 * @return bool True if the feature can be enabled, false otherwise.
+	 */
+	public function can_enable_feature(): bool {
+		$options = $this->parsely->get_options();
+
+		return true === $options['headline_testing']['enabled'] &&
+			'' !== $this->parsely->get_site_id();
+	}
+
+	/**
+	 * Enqueues the Headline Testing script, in accordance to the
+	 * installation_method option.
+	 *
+	 * @since 3.21.0
+	 */
+	public function enqueue_headline_testing_script(): void {
+		$options = $this->parsely->get_options();
+		$site_id = $this->parsely->get_site_id();
+
+		$headline_testing_options = $options['headline_testing'];
+		$installation_method      = $headline_testing_options['installation_method'];
+
+		if ( 'one_line' === $installation_method ) {
+			$this->enqueue_one_line_script( $headline_testing_options, $site_id );
+		} else {
+			$this->enqueue_advanced_script( $headline_testing_options, $site_id );
+		}
+	}
+
+	/**
+	 * Enqueues the one-line snippet script.
+	 *
+	 * @since 3.21.0
+	 *
+	 * @param Parsely_Options_Headline_Testing $options The headline testing options.
+	 * @param string                           $site_id The Parse.ly site ID.
+	 */
+	private function enqueue_one_line_script( $options, string $site_id ): void {
+		$script_url = 'https://experiments.parsely.com/vip-experiments.js?apiKey=' . rawurlencode( $site_id );
+
+		// Build data attributes string.
+		$data_attributes = array();
+
+		if ( $options['enable_live_updates'] ) {
+			$data_attributes[] = 'data-enable-live-updates="true"';
+
+			$timeout = absint( $options['live_update_timeout'] );
+			if ( 30000 !== $timeout ) {
+				$data_attributes[] = 'data-live-update-timeout="' . esc_attr( (string) $timeout ) . '"';
+			}
+		}
+
+		if ( $options['allow_after_content_load'] ) {
+			$data_attributes[] = 'data-allow-after-content-load="true"';
+		}
+
+		// Store data attributes and add filter to modify the script tag.
+		if ( count( $data_attributes ) > 0 ) {
+			$this->data_attributes = $data_attributes;
+
+			if ( false === has_filter(
+				'script_loader_tag',
+				array( $this, 'add_data_attributes_to_script_tag' )
+			) ) {
+				add_filter(
+					'script_loader_tag',
+					array( $this, 'add_data_attributes_to_script_tag' ),
+					10,
+					2
+				);
+			}
+		}
+
+		// Register and enqueue the script.
+		wp_register_script(
+			'parsely-headline-testing-one-line',
+			$script_url,
+			array(),
+			PARSELY_VERSION,
+			false
+		);
+
+		wp_enqueue_script( 'parsely-headline-testing-one-line' );
+	}
+
+	/**
+	 * Adds data attributes to the one-line script tag.
+	 *
+	 * @since 3.21.0
+	 *
+	 * @param string $tag    The script tag.
+	 * @param string $handle The script handle.
+	 * @return string The modified script tag.
+	 */
+	public function add_data_attributes_to_script_tag( string $tag, string $handle ): string {
+		if ( 'parsely-headline-testing-one-line' === $handle ) {
+			// Insert data attributes before the closing > of the script tag.
+			$tag = str_replace( '></script>', ' ' . implode( ' ', $this->data_attributes ) . '></script>', $tag );
+		}
+
+		return $tag;
+	}
+
+	/**
+	 * Enqueues the advanced installation script.
+	 *
+	 * @since 3.21.0
+	 *
+	 * @param Parsely_Options_Headline_Testing $options The headline testing options.
+	 * @param string                           $site_id The Parse.ly site ID.
+	 */
+	private function enqueue_advanced_script( $options, string $site_id ): void {
+		$config_options = array();
+
+		if ( $options['enable_flicker_control'] ) {
+			$config_options[] = 'enableFlickerControl: true';
+		}
+
+		if ( $options['enable_live_updates'] ) {
+			$config_options[] = 'enableLiveUpdates: true';
+
+			$timeout          = absint( $options['live_update_timeout'] );
+			$config_options[] = 'liveUpdateTimeout: ' . $timeout;
+		}
+
+		if ( $options['allow_after_content_load'] ) {
+			$config_options[] = 'allowAfterContentLoad: true';
+		}
+
+		$config_str = count( $config_options ) > 0 ? ', {' . implode( ', ', $config_options ) . '}' : '';
+
+		$script_content = '!function(){"use strict";var e=window.VIP_EXP=window.VIP_EXP||{config:{}};e.loadVIPExp=function(t){var n=arguments.length>1&&void 0!==arguments[1]?arguments[1]:{};t&&(e.config=n,e.config.apikey=t,function(e){if(!e)return;var t="https://experiments.parsely.com/vip-experiments.js"+"?apiKey=".concat(e),n=document.createElement("script");n.src=t,n.type="text/javascript",n.fetchPriority="high";var i=document.getElementsByTagName("script")[0];i&&i.parentNode&&i.parentNode.insertBefore(n,i)}(t),n.enableFlickerControl&&function(){var t,n;if(null!==(t=performance)&&void 0!==t&&null!==(n=t.getEntriesByName)&&void 0!==n&&null!==(n=n.call(t,"first-contentful-paint"))&&void 0!==n&&n[0])return;var i="vipexp-fooc-prevention";e.config.disableFlickerControl=function(){var e=document.getElementById(i);null!=e&&e.parentNode&&e.parentNode.removeChild(e)};var o=document.createElement("style");o.setAttribute("type","text/css"),o.appendChild(document.createTextNode("body { visibility: hidden; }")),o.id=i,document.head.appendChild(o),window.setTimeout(e.config.disableFlickerControl,500)}())},e.loadVIPExp("' . esc_js( $site_id ) . '"' . $config_str . ')}();';
+
+		// Register and enqueue the inline script.
+		wp_register_script(
+			'parsely-headline-testing-advanced',
+			'',
+			array(),
+			PARSELY_VERSION,
+			false
+		);
+
+		wp_add_inline_script( 'parsely-headline-testing-advanced', $script_content );
+		wp_enqueue_script( 'parsely-headline-testing-advanced' );
+	}
+}
diff --git a/src/class-parsely.php b/src/class-parsely.php
index 091a1f24c0..239cd18ab3 100644
--- a/src/class-parsely.php
+++ b/src/class-parsely.php
@@ -32,6 +32,7 @@
  *   custom_taxonomy_section: string,
  *   cats_as_tags: bool,
  *   content_helper: Parsely_Options_Content_Helper,
+ *   headline_testing: Parsely_Options_Headline_Testing,
  *   track_authenticated_users: bool,
  *   lowercase_tags: bool,
  *   force_https_canonicals: bool,
@@ -61,6 +62,15 @@
  *   allowed_user_roles: string[],
  * }
  *
+ * @phpstan-type Parsely_Options_Headline_Testing array{
+ *   enabled: bool,
+ *   installation_method: string,
+ *   enable_flicker_control: bool,
+ *   enable_live_updates: bool,
+ *   live_update_timeout: int,
+ *   allow_after_content_load: bool,
+ * }
+ *
  * @phpstan-type WP_HTTP_Request_Args array{
  *   method?: string,
  *   timeout?: float,
@@ -136,6 +146,14 @@ class Parsely {
 				'allowed_user_roles' => array( 'administrator' ),
 			),
 		),
+		'headline_testing'           => array(
+			'enabled'                  => false,
+			'installation_method'      => 'one_line',
+			'enable_flicker_control'   => false,
+			'enable_live_updates'      => false,
+			'live_update_timeout'      => 30000,
+			'allow_after_content_load' => false,
+		),
 		'track_authenticated_users'  => false,
 		'lowercase_tags'             => true,
 		'force_https_canonicals'     => false,
diff --git a/src/rest-api/settings/class-endpoint-headline-testing-settings.php b/src/rest-api/settings/class-endpoint-headline-testing-settings.php
new file mode 100644
index 0000000000..1312cc9311
--- /dev/null
+++ b/src/rest-api/settings/class-endpoint-headline-testing-settings.php
@@ -0,0 +1,80 @@
+<?php
+/**
+ * Headline Testing Settings Endpoint
+ *
+ * @package Parsely
+ * @since   3.21.0
+ */
+
+declare(strict_types=1);
+
+namespace Parsely\REST_API\Settings;
+
+use Parsely\REST_API\Settings\Base_Settings_Endpoint;
+
+/**
+ * Endpoint for managing Headline Testing settings.
+ *
+ * @since 3.21.0
+ *
+ * @phpstan-import-type Subvalue_Spec from Base_Settings_Endpoint
+ */
+class Endpoint_Headline_Testing_Settings extends Base_Settings_Endpoint {
+	/**
+	 * Returns the endpoint's name.
+	 *
+	 * @since 3.21.0
+	 *
+	 * @return string
+	 */
+	public static function get_endpoint_name(): string {
+		return 'headline-testing';
+	}
+
+	/**
+	 * Returns the meta entry's key.
+	 *
+	 * @since 3.21.0
+	 *
+	 * @return string The meta entry's key.
+	 */
+	protected function get_meta_key(): string {
+		return 'headline_testing';
+	}
+
+	/**
+	 * Returns the endpoint's subvalues specifications.
+	 *
+	 * @since 3.21.0
+	 *
+	 * @return array<string, Subvalue_Spec>
+	 */
+	protected function get_subvalues_specs(): array {
+		return array(
+			'enabled'                  => array(
+				'values'  => array( true, false ),
+				'default' => false,
+			),
+			'installation_method'      => array(
+				'values'  => array( 'one_line', 'advanced' ),
+				'default' => 'one_line',
+			),
+			'enable_flicker_control'   => array(
+				'values'  => array( true, false ),
+				'default' => false,
+			),
+			'enable_live_updates'      => array(
+				'values'  => array( true, false ),
+				'default' => false,
+			),
+			'live_update_timeout'      => array(
+				'values'  => range( 1000, 60000, 1000 ),
+				'default' => 30000,
+			),
+			'allow_after_content_load' => array(
+				'values'  => array( true, false ),
+				'default' => false,
+			),
+		);
+	}
+}
diff --git a/src/rest-api/settings/class-settings-controller.php b/src/rest-api/settings/class-settings-controller.php
index a7a37381db..d24ab4bbd0 100644
--- a/src/rest-api/settings/class-settings-controller.php
+++ b/src/rest-api/settings/class-settings-controller.php
@@ -41,6 +41,7 @@ public function init(): void {
 			new Endpoint_Dashboard_Widget_Settings( $this ),
 			new Endpoint_Editor_Sidebar_Settings( $this ),
 			new Endpoint_Traffic_Boost_Settings( $this ),
+			new Endpoint_Headline_Testing_Settings( $this ),
 		);
 
 		$this->register_endpoints( $endpoints );
diff --git a/tests/Integration/HeadlineTestingScriptsTest.php b/tests/Integration/HeadlineTestingScriptsTest.php
new file mode 100644
index 0000000000..c38caf1e53
--- /dev/null
+++ b/tests/Integration/HeadlineTestingScriptsTest.php
@@ -0,0 +1,487 @@
+<?php
+/**
+ * Integration Tests: Headline Testing scripts
+ *
+ * @package Parsely\Tests
+ * @since   3.21.0
+ */
+
+declare(strict_types=1);
+
+namespace Parsely\Tests\Integration;
+
+use Parsely\Parsely;
+use Parsely\Headline_Testing;
+
+use const Parsely\PARSELY_VERSION;
+
+/**
+ * Integration Tests for the Headline Testing scripts.
+ *
+ * @since 3.21.0
+ */
+final class HeadlineTestingScriptsTest extends TestCase {
+	/**
+	 * Headline_Testing object.
+	 *
+	 * @since 3.21.0
+	 *
+	 * @var Headline_Testing $headline_testing Holds the Headline_Testing object.
+	 */
+	private static $headline_testing;
+
+	/**
+	 * One-line script string used in assertions.
+	 *
+	 * @since 3.21.0
+	 *
+	 * @var string $one_line_script_string Holds the one-line script string.
+	 */
+	private static $one_line_script_string = 'src="https://experiments.parsely.com/vip-experiments.js?apiKey=demoaccount.parsely.com&amp;ver='
+		. PARSELY_VERSION . '" id="parsely-headline-testing-one-line-js"';
+
+	/**
+	 * Advanced script string used in assertions.
+	 *
+	 * @since 3.21.0
+	 *
+	 * @var string $advanced_script_string Holds the advanced script string.
+	 */
+	private static $advanced_script_string = 'id="parsely-headline-testing-advanced-js-after"';
+
+	/**
+	 * Setup method called before each test.
+	 *
+	 * @since 3.21.0
+	 */
+	public function set_up(): void {
+		global $wp_scripts;
+
+		parent::set_up();
+		TestCase::set_options();
+
+		// Reset WordPress scripts global to prevent state leakage between tests.
+		// phpcs:ignore WordPress.WP.GlobalVariablesOverride.Prohibited
+		$wp_scripts             = new \WP_Scripts();
+		self::$headline_testing = new Headline_Testing( new Parsely() );
+	}
+
+	/**
+	 * Verifies that the action is not being registered when the the feature is
+	 * disabled.
+	 *
+	 * @since 3.21.0
+	 *
+	 * @covers \Parsely\Headline_Testing::can_enable_feature
+	 * @covers \Parsely\Headline_Testing::enqueue_headline_testing_script
+	 * @covers \Parsely\Headline_Testing::enqueue_one_line_script
+	 * @covers \Parsely\Headline_Testing::run
+	 * @uses \Parsely\Headline_Testing::__construct
+	 * @uses \Parsely\Parsely::__construct
+	 * @uses \Parsely\Parsely::allow_parsely_remote_requests
+	 * @uses \Parsely\Parsely::are_credentials_managed
+	 * @uses \Parsely\Parsely::get_managed_credentials
+	 * @uses \Parsely\Parsely::get_options
+	 * @uses \Parsely\Parsely::get_site_id
+	 * @uses \Parsely\Parsely::set_default_content_helper_settings_values
+	 * @uses \Parsely\Parsely::set_default_full_metadata_in_non_posts
+	 * @uses \Parsely\Parsely::set_managed_options
+	 * @uses \Parsely\Parsely::site_id_is_set
+	 * @uses \Parsely\Permissions::build_pch_permissions_settings_array
+	 * @uses \Parsely\Permissions::get_user_roles_with_edit_posts_cap
+	 * @uses \Parsely\Services\Content_API\Content_API_Service::get_base_url
+	 * @uses \Parsely\Services\Suggestions_API\Suggestions_API_Service::get_base_url
+	 */
+	public function test_do_not_register_action_when_enabled_option_is_off(): void {
+		// Headline Testing should be off by default.
+		self::$headline_testing->run();
+		self::assertFalse(
+			has_action(
+				'wp_enqueue_scripts',
+				array( self::$headline_testing, 'enqueue_headline_testing_script' )
+			)
+		);
+	}
+
+	/**
+	 * Verifies that the action gets registered when the the feature is enabled.
+	 *
+	 * @since 3.21.0
+	 *
+	 * @covers \Parsely\Headline_Testing::can_enable_feature
+	 * @covers \Parsely\Headline_Testing::enqueue_headline_testing_script
+	 * @covers \Parsely\Headline_Testing::enqueue_one_line_script
+	 * @covers \Parsely\Headline_Testing::run
+	 * @uses \Parsely\Headline_Testing::__construct
+	 * @uses \Parsely\Parsely::__construct
+	 * @uses \Parsely\Parsely::allow_parsely_remote_requests
+	 * @uses \Parsely\Parsely::are_credentials_managed
+	 * @uses \Parsely\Parsely::get_managed_credentials
+	 * @uses \Parsely\Parsely::get_options
+	 * @uses \Parsely\Parsely::get_site_id
+	 * @uses \Parsely\Parsely::set_default_content_helper_settings_values
+	 * @uses \Parsely\Parsely::set_default_full_metadata_in_non_posts
+	 * @uses \Parsely\Parsely::set_managed_options
+	 * @uses \Parsely\Parsely::site_id_is_set
+	 * @uses \Parsely\Permissions::build_pch_permissions_settings_array
+	 * @uses \Parsely\Permissions::get_user_roles_with_edit_posts_cap
+	 * @uses \Parsely\Services\Content_API\Content_API_Service::get_base_url
+	 * @uses \Parsely\Services\Suggestions_API\Suggestions_API_Service::get_base_url
+	 */
+	public function test_register_action_when_enabled_option_is_on(): void {
+		TestCase::set_options( array( 'headline_testing' => array( 'enabled' => true ) ) );
+		self::$headline_testing->run();
+
+		self::assertSame(
+			10,
+			has_action(
+				'wp_enqueue_scripts',
+				array( self::$headline_testing, 'enqueue_headline_testing_script' )
+			)
+		);
+	}
+
+	/**
+	 * Verifies that run() does not register the action when no Site ID is set.
+	 *
+	 * @since 3.21.0
+	 *
+	 * @covers \Parsely\Headline_Testing::can_enable_feature
+	 * @covers \Parsely\Headline_Testing::run
+	 * @uses \Parsely\Headline_Testing::__construct
+	 * @uses \Parsely\Parsely::__construct
+	 * @uses \Parsely\Parsely::allow_parsely_remote_requests
+	 * @uses \Parsely\Parsely::are_credentials_managed
+	 * @uses \Parsely\Parsely::get_managed_credentials
+	 * @uses \Parsely\Parsely::get_options
+	 * @uses \Parsely\Parsely::get_site_id
+	 * @uses \Parsely\Parsely::set_default_content_helper_settings_values
+	 * @uses \Parsely\Parsely::set_default_full_metadata_in_non_posts
+	 * @uses \Parsely\Parsely::set_managed_options
+	 * @uses \Parsely\Parsely::site_id_is_set
+	 * @uses \Parsely\Permissions::build_pch_permissions_settings_array
+	 * @uses \Parsely\Permissions::get_user_roles_with_edit_posts_cap
+	 * @uses \Parsely\Services\Content_API\Content_API_Service::get_base_url
+	 * @uses \Parsely\Services\Suggestions_API\Suggestions_API_Service::get_base_url
+	 */
+	public function test_do_not_register_action_when_no_site_id_is_set(): void {
+		TestCase::set_options(
+			array(
+				'apikey'           => '',
+				'headline_testing' => array( 'enabled' => true ),
+			)
+		);
+
+		self::$headline_testing->run();
+
+		// Should not be enqueued as the Site ID is empty.
+		self::assertFalse(
+			has_action(
+				'wp_enqueue_scripts',
+				array( self::$headline_testing, 'enqueue_headline_testing_script' )
+			)
+		);
+	}
+
+	/**
+	 * Verifies that enqueuing functionality works as expected.
+	 *
+	 * @since 3.21.0
+	 *
+	 * @covers \Parsely\Headline_Testing::can_enable_feature
+	 * @covers \Parsely\Headline_Testing::enqueue_headline_testing_script
+	 * @covers \Parsely\Headline_Testing::enqueue_one_line_script
+	 * @covers \Parsely\Headline_Testing::run
+	 * @uses \Parsely\Headline_Testing::__construct
+	 * @uses \Parsely\Parsely::__construct
+	 * @uses \Parsely\Parsely::allow_parsely_remote_requests
+	 * @uses \Parsely\Parsely::are_credentials_managed
+	 * @uses \Parsely\Parsely::get_default_options
+	 * @uses \Parsely\Parsely::get_managed_credentials
+	 * @uses \Parsely\Parsely::get_options
+	 * @uses \Parsely\Parsely::get_site_id
+	 * @uses \Parsely\Parsely::set_default_content_helper_settings_values
+	 * @uses \Parsely\Parsely::set_default_full_metadata_in_non_posts
+	 * @uses \Parsely\Parsely::set_managed_options
+	 * @uses \Parsely\Parsely::site_id_is_set
+	 * @uses \Parsely\Permissions::build_pch_permissions_settings_array
+	 * @uses \Parsely\Permissions::get_user_roles_with_edit_posts_cap
+	 * @uses \Parsely\Services\Content_API\Content_API_Service::get_base_url
+	 * @uses \Parsely\Services\Suggestions_API\Suggestions_API_Service::get_base_url
+	 */
+	public function test_script_is_registered_and_enqueued(): void {
+		$this->enable_headline_testing();
+
+		self::$headline_testing->run();
+
+		// phpcs:ignore WordPress.NamingConventions.PrefixAllGlobals.NonPrefixedHooknameFound
+		do_action( 'wp_enqueue_scripts' );
+
+		// Should be enqueued as the headline testing option is enabled and the Site ID is set.
+		$this->assert_is_script_registered( 'parsely-headline-testing-one-line' );
+		$this->assert_is_script_enqueued( 'parsely-headline-testing-one-line' );
+	}
+
+	/**
+	 * Verifies that the HTML markup is correctly output when using the one-line
+	 * script.
+	 *
+	 * @since 3.21.0
+	 *
+	 * @covers \Parsely\Headline_Testing::can_enable_feature
+	 * @covers \Parsely\Headline_Testing::enqueue_headline_testing_script
+	 * @covers \Parsely\Headline_Testing::enqueue_one_line_script
+	 * @covers \Parsely\Headline_Testing::run
+	 * @uses \Parsely\Headline_Testing::__construct
+	 * @uses \Parsely\Parsely::__construct
+	 * @uses \Parsely\Parsely::allow_parsely_remote_requests
+	 * @uses \Parsely\Parsely::are_credentials_managed
+	 * @uses \Parsely\Parsely::get_default_options
+	 * @uses \Parsely\Parsely::get_managed_credentials
+	 * @uses \Parsely\Parsely::get_options
+	 * @uses \Parsely\Parsely::get_site_id
+	 * @uses \Parsely\Parsely::set_default_content_helper_settings_values
+	 * @uses \Parsely\Parsely::set_default_full_metadata_in_non_posts
+	 * @uses \Parsely\Parsely::set_managed_options
+	 * @uses \Parsely\Parsely::site_id_is_set
+	 * @uses \Parsely\Permissions::build_pch_permissions_settings_array
+	 * @uses \Parsely\Permissions::get_user_roles_with_edit_posts_cap
+	 * @uses \Parsely\Services\Content_API\Content_API_Service::get_base_url
+	 * @uses \Parsely\Services\Suggestions_API\Suggestions_API_Service::get_base_url
+	 */
+	public function test_markup_with_one_line_script_installation_method(): void {
+		$this->enable_headline_testing();
+
+		self::$headline_testing->run();
+
+		// phpcs:ignore WordPress.NamingConventions.PrefixAllGlobals.NonPrefixedHooknameFound
+		do_action( 'wp_enqueue_scripts' );
+
+		ob_start();
+		wp_print_scripts();
+		$output = (string) ob_get_clean();
+
+		// Markup should contain the one-line script and not the advanced script.
+		self::assertStringContainsString( self::$one_line_script_string, $output );
+		self::assertStringNotContainsString( self::$advanced_script_string, $output );
+	}
+
+	/**
+	 * Verifies that the HTML markup is correctly output when using the one-line
+	 * script with an additional option.
+	 *
+	 * @since 3.21.0
+	 *
+	 * @covers \Parsely\Headline_Testing::can_enable_feature
+	 * @covers \Parsely\Headline_Testing::enqueue_headline_testing_script
+	 * @covers \Parsely\Headline_Testing::enqueue_one_line_script
+	 * @covers \Parsely\Headline_Testing::add_data_attributes_to_script_tag
+	 * @covers \Parsely\Headline_Testing::run
+	 * @uses \Parsely\Headline_Testing::__construct
+	 * @uses \Parsely\Parsely::__construct
+	 * @uses \Parsely\Parsely::allow_parsely_remote_requests
+	 * @uses \Parsely\Parsely::are_credentials_managed
+	 * @uses \Parsely\Parsely::get_default_options
+	 * @uses \Parsely\Parsely::get_managed_credentials
+	 * @uses \Parsely\Parsely::get_options
+	 * @uses \Parsely\Parsely::get_site_id
+	 * @uses \Parsely\Parsely::set_default_content_helper_settings_values
+	 * @uses \Parsely\Parsely::set_default_full_metadata_in_non_posts
+	 * @uses \Parsely\Parsely::set_managed_options
+	 * @uses \Parsely\Parsely::site_id_is_set
+	 * @uses \Parsely\Permissions::build_pch_permissions_settings_array
+	 * @uses \Parsely\Permissions::get_user_roles_with_edit_posts_cap
+	 * @uses \Parsely\Services\Content_API\Content_API_Service::get_base_url
+	 * @uses \Parsely\Services\Suggestions_API\Suggestions_API_Service::get_base_url
+	 */
+	public function test_markup_with_one_line_script_and_additional_option(): void {
+		$this->enable_headline_testing( array( 'enable_live_updates' => true ) );
+
+		self::$headline_testing->run();
+
+		// phpcs:ignore WordPress.NamingConventions.PrefixAllGlobals.NonPrefixedHooknameFound
+		do_action( 'wp_enqueue_scripts' );
+
+		ob_start();
+		wp_print_scripts();
+		$output = (string) ob_get_clean();
+
+		// Markup should contain the one-line script with the option's attribute.
+		self::assertStringContainsString(
+			self::$one_line_script_string . ' data-enable-live-updates="true"',
+			$output
+		);
+		self::assertStringNotContainsString( self::$advanced_script_string, $output );
+	}
+
+	/**
+	 * Verifies that running multiple wp_enqueue_scripts actions doesn't add
+	 * duplicate attributes to the script markup.
+	 *
+	 * @since 3.21.0
+	 *
+	 * @covers \Parsely\Headline_Testing::can_enable_feature
+	 * @covers \Parsely\Headline_Testing::enqueue_headline_testing_script
+	 * @covers \Parsely\Headline_Testing::enqueue_one_line_script
+	 * @covers \Parsely\Headline_Testing::add_data_attributes_to_script_tag
+	 * @covers \Parsely\Headline_Testing::run
+	 * @uses \Parsely\Headline_Testing::__construct
+	 * @uses \Parsely\Parsely::__construct
+	 * @uses \Parsely\Parsely::allow_parsely_remote_requests
+	 * @uses \Parsely\Parsely::are_credentials_managed
+	 * @uses \Parsely\Parsely::get_default_options
+	 * @uses \Parsely\Parsely::get_managed_credentials
+	 * @uses \Parsely\Parsely::get_options
+	 * @uses \Parsely\Parsely::get_site_id
+	 * @uses \Parsely\Parsely::set_default_content_helper_settings_values
+	 * @uses \Parsely\Parsely::set_default_full_metadata_in_non_posts
+	 * @uses \Parsely\Parsely::set_managed_options
+	 * @uses \Parsely\Parsely::site_id_is_set
+	 * @uses \Parsely\Permissions::build_pch_permissions_settings_array
+	 * @uses \Parsely\Permissions::get_user_roles_with_edit_posts_cap
+	 * @uses \Parsely\Services\Content_API\Content_API_Service::get_base_url
+	 * @uses \Parsely\Services\Suggestions_API\Suggestions_API_Service::get_base_url
+	 */
+	public function test_firing_multiple_wp_enqueue_scripts_does_not_duplicate_attributes(): void {
+		$this->enable_headline_testing( array( 'enable_live_updates' => true ) );
+
+		self::$headline_testing->run();
+
+		// Trigger wp_enqueue_scripts multiple times.
+		// phpcs:ignore WordPress.NamingConventions.PrefixAllGlobals.NonPrefixedHooknameFound
+		do_action( 'wp_enqueue_scripts' );
+		// phpcs:ignore WordPress.NamingConventions.PrefixAllGlobals.NonPrefixedHooknameFound
+		do_action( 'wp_enqueue_scripts' );
+		// phpcs:ignore WordPress.NamingConventions.PrefixAllGlobals.NonPrefixedHooknameFound
+		do_action( 'wp_enqueue_scripts' );
+
+		ob_start();
+		wp_print_scripts();
+		$output = (string) ob_get_clean();
+
+		// Markup should contain the option's attribute only once.
+		self::assertStringContainsString( 'data-enable-live-updates="true"', $output );
+		$count = substr_count( $output, 'data-enable-live-updates="true"' );
+		self::assertSame(
+			1,
+			$count,
+			'The data-enable-live-updates attribute should appear exactly once, but appeared ' . $count . ' times.'
+		);
+	}
+
+	/**
+	 * Verifies that the HTML markup is correctly output when using the advanced
+	 * script.
+	 *
+	 * @since 3.21.0
+	 *
+	 * @covers \Parsely\Headline_Testing::can_enable_feature
+	 * @covers \Parsely\Headline_Testing::enqueue_headline_testing_script
+	 * @covers \Parsely\Headline_Testing::enqueue_advanced_script
+	 * @covers \Parsely\Headline_Testing::run
+	 * @uses \Parsely\Headline_Testing::__construct
+	 * @uses \Parsely\Parsely::__construct
+	 * @uses \Parsely\Parsely::allow_parsely_remote_requests
+	 * @uses \Parsely\Parsely::are_credentials_managed
+	 * @uses \Parsely\Parsely::get_default_options
+	 * @uses \Parsely\Parsely::get_managed_credentials
+	 * @uses \Parsely\Parsely::get_options
+	 * @uses \Parsely\Parsely::get_site_id
+	 * @uses \Parsely\Parsely::set_default_content_helper_settings_values
+	 * @uses \Parsely\Parsely::set_default_full_metadata_in_non_posts
+	 * @uses \Parsely\Parsely::set_managed_options
+	 * @uses \Parsely\Parsely::site_id_is_set
+	 * @uses \Parsely\Permissions::build_pch_permissions_settings_array
+	 * @uses \Parsely\Permissions::get_user_roles_with_edit_posts_cap
+	 * @uses \Parsely\Services\Content_API\Content_API_Service::get_base_url
+	 * @uses \Parsely\Services\Suggestions_API\Suggestions_API_Service::get_base_url
+	 */
+	public function test_markup_with_advanced_script_installation_method(): void {
+		$this->enable_headline_testing( array( 'installation_method' => 'advanced' ) );
+
+		self::$headline_testing->run();
+
+		// phpcs:ignore WordPress.NamingConventions.PrefixAllGlobals.NonPrefixedHooknameFound
+		do_action( 'wp_enqueue_scripts' );
+
+		ob_start();
+		wp_print_scripts();
+		$output = (string) ob_get_clean();
+
+		// Markup should contain the advanced script and not the one-line script.
+		self::assertStringContainsString( self::$advanced_script_string, $output );
+		self::assertStringNotContainsString( self::$one_line_script_string, $output );
+	}
+
+	/**
+	 * Verifies that the HTML markup is correctly output when using the advanced
+	 * script with an additional option.
+	 *
+	 * @since 3.21.0
+	 *
+	 * @covers \Parsely\Headline_Testing::can_enable_feature
+	 * @covers \Parsely\Headline_Testing::enqueue_headline_testing_script
+	 * @covers \Parsely\Headline_Testing::enqueue_advanced_script
+	 * @covers \Parsely\Headline_Testing::run
+	 * @uses \Parsely\Headline_Testing::__construct
+	 * @uses \Parsely\Parsely::__construct
+	 * @uses \Parsely\Parsely::allow_parsely_remote_requests
+	 * @uses \Parsely\Parsely::are_credentials_managed
+	 * @uses \Parsely\Parsely::get_default_options
+	 * @uses \Parsely\Parsely::get_managed_credentials
+	 * @uses \Parsely\Parsely::get_options
+	 * @uses \Parsely\Parsely::get_site_id
+	 * @uses \Parsely\Parsely::set_default_content_helper_settings_values
+	 * @uses \Parsely\Parsely::set_default_full_metadata_in_non_posts
+	 * @uses \Parsely\Parsely::set_managed_options
+	 * @uses \Parsely\Parsely::site_id_is_set
+	 * @uses \Parsely\Permissions::build_pch_permissions_settings_array
+	 * @uses \Parsely\Permissions::get_user_roles_with_edit_posts_cap
+	 * @uses \Parsely\Services\Content_API\Content_API_Service::get_base_url
+	 * @uses \Parsely\Services\Suggestions_API\Suggestions_API_Service::get_base_url
+	 */
+	public function test_markup_with_advanced_script_and_additional_option(): void {
+		$this->enable_headline_testing(
+			array(
+				'installation_method' => 'advanced',
+				'enable_live_updates' => true,
+			)
+		);
+
+		self::$headline_testing->run();
+
+		// phpcs:ignore WordPress.NamingConventions.PrefixAllGlobals.NonPrefixedHooknameFound
+		do_action( 'wp_enqueue_scripts' );
+
+		ob_start();
+		wp_print_scripts();
+		$output = (string) ob_get_clean();
+
+		// Markup should contain the advanced script with the option's config.
+		self::assertStringContainsString( self::$advanced_script_string, $output );
+		self::assertStringContainsString( 'enableLiveUpdates: true', $output );
+		self::assertStringNotContainsString( self::$one_line_script_string, $output );
+	}
+
+	/**
+	 * Adds Headline Testing feature options, setting the feature to enabled and
+	 * respecting any passed setting values.
+	 *
+	 * Default values will be used for any unspecified settings.
+	 *
+	 * @since 3.21.0
+	 *
+	 * @param array<string, mixed> $settings Custom settings to save.
+	 */
+	private function enable_headline_testing( array $settings = array() ): void {
+		TestCase::set_options(
+			array(
+				'headline_testing' => array_merge(
+					( new Parsely() )->get_default_options()['headline_testing'],
+					array( 'enabled' => true ),
+					$settings
+				),
+			)
+		);
+	}
+}
diff --git a/tests/e2e/specs/activation-flow.spec.ts b/tests/e2e/specs/activation-flow.spec.ts
index 789cde3f7d..c38e5dde29 100644
--- a/tests/e2e/specs/activation-flow.spec.ts
+++ b/tests/e2e/specs/activation-flow.spec.ts
@@ -59,6 +59,8 @@ test.describe( 'Activation flow', (): void => {
 		const basicSection = page.locator( '.basic-section' );
 		const contentHelperTab = page.getByRole( 'link', { name: 'Content Intelligence' } );
 		const contentHelperSection = page.locator( '.content-intelligence-section' );
+		const headlineTestingTab = page.getByRole( 'link', { name: 'Headline Testing' } );
+		const headlineTestingSection = page.locator( '.headline-testing-section' );
 		const recrawlTab = page.getByRole( 'link', { name: 'Recrawl' } );
 		const recrawlSection = page.locator( '.recrawl-section' );
 		const advancedTab = page.getByRole( 'link', { name: 'Advanced' } );
@@ -67,41 +69,55 @@ test.describe( 'Activation flow', (): void => {
 		// Check that all tabs are present in the Settings page.
 		await expect( basicTab ).toBeVisible();
 		await expect( contentHelperTab ).toBeVisible();
+		await expect( headlineTestingTab ).toBeVisible();
 		await expect( recrawlTab ).toBeVisible();
 		await expect( advancedTab ).toBeVisible();
 
 		// Check that by default, the Basic Settings section is active.
 		await expect( basicSection ).toBeVisible();
 		await expect( contentHelperSection ).toBeHidden();
+		await expect( headlineTestingSection ).toBeHidden();
 		await expect( recrawlSection ).toBeHidden();
 		await expect( advancedSection ).toBeHidden();
 
-		// Test section visibility when the Basic tab is clicked.
-		await basicSection.click();
-		await expect( basicSection ).toBeVisible();
-		await expect( contentHelperSection ).toBeHidden();
+		// Test section visibility when the Content Intelligence tab is clicked.
+		await contentHelperTab.click();
+		await contentHelperSection.waitFor( { state: 'visible' } );
+		await expect( basicSection ).toBeHidden();
+		await expect( headlineTestingSection ).toBeHidden();
 		await expect( recrawlSection ).toBeHidden();
 		await expect( advancedSection ).toBeHidden();
 
-		// Test section visibility when the Content Intelligence tab is clicked.
-		await contentHelperTab.click();
+		// Test section visibility when the Headline Testing tab is clicked.
+		await headlineTestingTab.click();
+		await headlineTestingSection.waitFor( { state: 'visible' } );
 		await expect( basicSection ).toBeHidden();
-		await expect( contentHelperSection ).toBeVisible();
+		await expect( contentHelperSection ).toBeHidden();
 		await expect( recrawlSection ).toBeHidden();
 		await expect( advancedSection ).toBeHidden();
 
 		// Test section visibility when the Recrawl tab is clicked.
 		await recrawlTab.click();
+		await recrawlSection.waitFor( { state: 'visible' } );
 		await expect( basicSection ).toBeHidden();
 		await expect( contentHelperSection ).toBeHidden();
-		await expect( recrawlSection ).toBeVisible();
+		await expect( headlineTestingSection ).toBeHidden();
 		await expect( advancedSection ).toBeHidden();
 
 		// Test section visibility when the Advanced tab is clicked.
 		await advancedTab.click();
+		await advancedSection.waitFor( { state: 'visible' } );
 		await expect( basicSection ).toBeHidden();
 		await expect( contentHelperSection ).toBeHidden();
+		await expect( headlineTestingSection ).toBeHidden();
 		await expect( recrawlSection ).toBeHidden();
-		await expect( advancedSection ).toBeVisible();
+
+		// Test section visibility when the Basic tab is clicked.
+		await basicTab.click();
+		await basicSection.waitFor( { state: 'visible' } );
+		await expect( contentHelperSection ).toBeHidden();
+		await expect( headlineTestingSection ).toBeHidden();
+		await expect( recrawlSection ).toBeHidden();
+		await expect( advancedSection ).toBeHidden();
 	} );
 } );
diff --git a/wp-parsely.php b/wp-parsely.php
index 7487e97768..0080e7a63c 100644
--- a/wp-parsely.php
+++ b/wp-parsely.php
@@ -31,6 +31,7 @@
 use Parsely\Content_Helper\Post_List_Stats;
 use Parsely\Endpoints\GraphQL_Metadata;
 use Parsely\Endpoints\Rest_Metadata;
+use Parsely\Headline_Testing;
 use Parsely\Integrations\Amp;
 use Parsely\Integrations\Google_Web_Stories;
 use Parsely\Integrations\Integrations;
@@ -97,6 +98,10 @@ function parsely_initialize_plugin(): void {
 
 	$metadata_renderer = new Metadata_Renderer( $parsely );
 	$metadata_renderer->run();
+
+	// Initialize Headline Testing feature.
+	$headline_testing = new Headline_Testing( $parsely );
+	$headline_testing->run();
 }
 
 add_action( 'admin_init', __NAMESPACE__ . '\\parsely_admin_init_register' );