diff --git a/includes/Core/Authentication/Authentication.php b/includes/Core/Authentication/Authentication.php
index cc088be0f6b..3e27c9e47e7 100644
--- a/includes/Core/Authentication/Authentication.php
+++ b/includes/Core/Authentication/Authentication.php
@@ -284,7 +284,9 @@ public function register() {
 		add_filter( 'googlesitekit_setup_data', $this->get_method_proxy( 'inline_js_setup_data' ) );
 
 		add_action( 'admin_init', $this->get_method_proxy( 'handle_oauth' ) );
-		add_action( 'admin_init', $this->get_method_proxy( 'check_connected_proxy_url' ) );
+		// Run after the connected proxy URL migration (default priority) so it
+		// encodes the stored value before this check compares it to the site URL.
+		add_action( 'admin_init', $this->get_method_proxy( 'check_connected_proxy_url' ), 20 );
 
 		add_action( 'admin_action_' . self::ACTION_CONNECT, $this->get_method_proxy( 'handle_connect' ) );
 		add_action( 'admin_action_' . self::ACTION_DISCONNECT, $this->get_method_proxy( 'handle_disconnect' ) );
diff --git a/includes/Core/Authentication/Connected_Proxy_URL.php b/includes/Core/Authentication/Connected_Proxy_URL.php
index b811ece498b..fbcc5924391 100644
--- a/includes/Core/Authentication/Connected_Proxy_URL.php
+++ b/includes/Core/Authentication/Connected_Proxy_URL.php
@@ -30,24 +30,45 @@ class Connected_Proxy_URL extends Setting {
 	 * Matches provided URL with the current proxy URL in the settings.
 	 *
 	 * @since 1.17.0
+	 * @since n.e.x.t Compares the given URL against the decoded stored URL.
 	 *
 	 * @param string $url URL to match against the current one in the settings.
 	 * @return bool TRUE if URL matches the current one, otherwise FALSE.
 	 */
 	public function matches_url( $url ) {
-		$sanitize   = $this->get_sanitize_callback();
-		$normalized = $sanitize( $url );
-		return $normalized === $this->get();
+		return trailingslashit( $url ) === $this->get();
 	}
 
 	/**
-	 * Gets the callback for sanitizing the setting's value before saving.
+	 * Gets the connected proxy URL, decoded from the form the option holds.
 	 *
-	 * @since 1.17.0
+	 * A stored value that fails to decode reads as no value at all, so a
+	 * corrupted option sends the site back through the connection flow rather
+	 * than through a comparison against an unreadable URL.
+	 *
+	 * @since n.e.x.t
+	 *
+	 * @return string|bool Connected proxy URL, or FALSE when the option holds
+	 *                     no value or one that fails to decode.
+	 */
+	public function get() {
+		$stored_url = parent::get();
+
+		return is_string( $stored_url ) ? base64_decode( $stored_url, true ) : $stored_url;
+	}
+
+	/**
+	 * Sets the connected proxy URL.
+	 *
+	 * We encode the URL to prevent database-wide search-and-replace tasks
+	 * from changing the URL used to connect to the Site Kit Proxy service.
+	 *
+	 * @since n.e.x.t
 	 *
-	 * @return callable A sanitizing function.
+	 * @param string $value Connected proxy URL.
+	 * @return bool TRUE on success, FALSE on failure.
 	 */
-	protected function get_sanitize_callback() {
-		return 'trailingslashit';
+	public function set( $value ) {
+		return parent::set( base64_encode( trailingslashit( $value ) ) );
 	}
 }
diff --git a/includes/Core/Util/Migration_N_E_X_T.php b/includes/Core/Util/Migration_N_E_X_T.php
new file mode 100644
index 00000000000..13f861b1784
--- /dev/null
+++ b/includes/Core/Util/Migration_N_E_X_T.php
@@ -0,0 +1,109 @@
+<?php
+/**
+ * Migration for the connected proxy URL setting.
+ *
+ * @package   Google\Site_Kit\Core\Util
+ * @copyright 2026 Google LLC
+ * @license   https://www.apache.org/licenses/LICENSE-2.0 Apache License 2.0
+ * @link      https://sitekit.withgoogle.com
+ */
+
+namespace Google\Site_Kit\Core\Util;
+
+use Google\Site_Kit\Context;
+use Google\Site_Kit\Core\Authentication\Connected_Proxy_URL;
+use Google\Site_Kit\Core\Storage\Options;
+
+/**
+ * Class Migration_N_E_X_T.
+ *
+ * @since n.e.x.t
+ * @access private
+ * @ignore
+ */
+class Migration_N_E_X_T {
+	/**
+	 * Target DB version.
+	 */
+	const DB_VERSION = 'n.e.x.t';
+
+	/**
+	 * DB version option name.
+	 */
+	const DB_VERSION_OPTION = 'googlesitekit_db_version';
+
+	/**
+	 * Options instance.
+	 *
+	 * @since n.e.x.t
+	 * @var Options
+	 */
+	protected Options $options;
+
+	/**
+	 * Connected_Proxy_URL instance.
+	 *
+	 * @since n.e.x.t
+	 * @var Connected_Proxy_URL
+	 */
+	protected Connected_Proxy_URL $connected_proxy_url;
+
+	/**
+	 * Constructor.
+	 *
+	 * @since n.e.x.t
+	 *
+	 * @param Context $context Plugin context instance.
+	 * @param Options $options Optional. Options instance.
+	 */
+	public function __construct(
+		Context $context,
+		?Options $options = null
+	) {
+		$this->options             = $options ?: new Options( $context );
+		$this->connected_proxy_url = new Connected_Proxy_URL( $this->options );
+	}
+
+	/**
+	 * Registers hooks.
+	 *
+	 * @since n.e.x.t
+	 */
+	public function register() {
+		add_action( 'admin_init', array( $this, 'migrate' ) );
+	}
+
+	/**
+	 * Migrates the DB.
+	 *
+	 * @since n.e.x.t
+	 */
+	public function migrate() {
+		$db_version = $this->options->get( self::DB_VERSION_OPTION );
+
+		if ( ! $db_version || version_compare( $db_version, self::DB_VERSION, '<' ) ) {
+			$this->migrate_connected_proxy_url();
+
+			$this->options->set( self::DB_VERSION_OPTION, self::DB_VERSION );
+		}
+	}
+
+	/**
+	 * Migrates a plain text connected proxy URL to the encoded format.
+	 *
+	 * Earlier plugin versions stored the URL in plain text. A stored value that
+	 * still starts with its scheme goes back through Connected_Proxy_URL::set(),
+	 * which stores it encoded.
+	 *
+	 * @since n.e.x.t
+	 */
+	protected function migrate_connected_proxy_url() {
+		$stored_url = $this->options->get( Connected_Proxy_URL::OPTION );
+
+		if ( ! is_string( $stored_url ) || 0 !== strpos( $stored_url, 'http' ) ) {
+			return;
+		}
+
+		$this->connected_proxy_url->set( $stored_url );
+	}
+}
diff --git a/includes/Plugin.php b/includes/Plugin.php
index 4ca0114edb9..3750f5ab81a 100644
--- a/includes/Plugin.php
+++ b/includes/Plugin.php
@@ -241,6 +241,7 @@ function () use ( $options, $activation_flag ) {
 				( new Core\Util\Migration_1_150_0( $this->context, $options ) )->register();
 				( new Core\Util\Migration_1_163_0( $this->context, $options ) )->register();
 				( new Core\Util\Migration_1_177_0( $this->context, $options ) )->register();
+				( new Core\Util\Migration_N_E_X_T( $this->context, $options ) )->register();
 				( new Core\Dashboard_Sharing\Dashboard_Sharing( $this->context ) )->register();
 				( new Core\Key_Metrics\Key_Metrics( $this->context, $user_options, $options ) )->register();
 				( new Core\Prompts\Prompts( $this->context, $user_options ) )->register();
diff --git a/tests/phpunit/integration/Core/Authentication/AuthenticationTest.php b/tests/phpunit/integration/Core/Authentication/AuthenticationTest.php
index 0b18d44ade5..7159e863f6f 100644
--- a/tests/phpunit/integration/Core/Authentication/AuthenticationTest.php
+++ b/tests/phpunit/integration/Core/Authentication/AuthenticationTest.php
@@ -692,7 +692,7 @@ public function test_set_connected_proxy_url() {
 		do_action( 'googlesitekit_authorize_user', array(), array(), array() );
 		remove_filter( 'home_url', $home_url_hook );
 
-		$this->assertEquals( 'https://example.com/subsite/', $options->get( Connected_Proxy_URL::OPTION ), 'Connected proxy URL should be set to filtered home_url.' ); // PHPCS: line 692.
+		$this->assertEquals( base64_encode( 'https://example.com/subsite/' ), $options->get( Connected_Proxy_URL::OPTION ), 'The `set()` method should store the connected proxy URL base64-encoded from the filtered home_url.' ); // PHPCS: line 692.
 	}
 
 	public function test_check_connected_proxy_url() {
@@ -735,6 +735,51 @@ function ( $caps ) {
 		);
 	}
 
+	public function test_check_connected_proxy_url__after_the_home_url_changes() {
+		remove_all_actions( 'admin_init' );
+
+		$user_id = $this->factory()->user->create( array( 'role' => 'administrator' ) );
+		wp_set_current_user( $user_id );
+
+		$context      = new Context( GOOGLESITEKIT_PLUGIN_MAIN_FILE );
+		$options      = new Options( $context );
+		$user_options = new User_Options( $context );
+
+		$authentication = new Authentication( $context, $options, $user_options );
+		$authentication->register();
+
+		// Connect the site with the home URL it runs on.
+		$authentication->get_connected_proxy_url_instance()->set( $context->get_canonical_home_url() );
+
+		// Emulate credentials.
+		$this->fake_proxy_site_connection();
+
+		// Emulate OAuth access token.
+		$authentication->get_oauth_client()->set_token( array( 'access_token' => 'valid-auth-token' ) );
+
+		// Grant the administrator the Permissions::SETUP capability regardless
+		// of authentication.
+		add_filter(
+			'user_has_cap',
+			function ( $caps ) {
+				$caps[ Permissions::SETUP ] = true;
+				return $caps;
+			}
+		);
+
+		// Move the site to another domain, as a search and replace over the
+		// database does.
+		update_option( 'home', 'https://new-domain.example.com' );
+
+		do_action( 'admin_init' );
+
+		$this->assertEquals(
+			Disconnected_Reason::REASON_CONNECTED_URL_MISMATCH,
+			$user_options->get( Disconnected_Reason::OPTION ),
+			'Site Kit should flag the URL change once the home URL moves to another domain.'
+		);
+	}
+
 	/**
 	 * Test handle_proxy_permissions().
 	 */
diff --git a/tests/phpunit/integration/Core/Authentication/Connected_Proxy_URLTest.php b/tests/phpunit/integration/Core/Authentication/Connected_Proxy_URLTest.php
index d8258df6e1b..cbd61434f4e 100644
--- a/tests/phpunit/integration/Core/Authentication/Connected_Proxy_URLTest.php
+++ b/tests/phpunit/integration/Core/Authentication/Connected_Proxy_URLTest.php
@@ -2,11 +2,11 @@
 /**
  * Class Google\Site_Kit\Core\Authentication\Connected_Proxy_URLTest
  *
- * @package   Google\Site_Kit
+ * @package   Google\Site_Kit\Tests\Core\Authentication
  * @copyright 2021 Google LLC
  * @license   https://www.apache.org/licenses/LICENSE-2.0 Apache License 2.0
  * @link      https://sitekit.withgoogle.com
- * */
+ */
 
 namespace Google\Site_Kit\Tests\Core\Authentication;
 
@@ -48,6 +48,58 @@ public function test_matches_url() {
 		$this->assertTrue( $connected_proxy_url->matches_url( 'https://example.com/' ), 'URL should match when both have trailing slashes.' );
 	}
 
+	public function test_matches_url__after_a_database_search_and_replace() {
+		$connected_proxy_url = new Connected_Proxy_URL( $this->options );
+		$connected_proxy_url->register();
+
+		$connected_proxy_url->set( 'https://old-site.example.com' );
+
+		// Simulate a database search and replace of the site domain.
+		$stored_url    = $this->options->get( Connected_Proxy_URL::OPTION );
+		$rewritten_url = str_replace( 'old-site.example.com', 'new-site.example.com', $stored_url );
+
+		$this->assertSame( $stored_url, $rewritten_url, 'A search and replace should find no domain to rewrite inside the stored value.' );
+		$this->assertTrue( $connected_proxy_url->matches_url( 'https://old-site.example.com' ), 'The stored URL should still match the connected URL after a search and replace.' );
+	}
+
+	public function test_set__stores_an_encoded_url() {
+		$connected_proxy_url = new Connected_Proxy_URL( $this->options );
+		$connected_proxy_url->register();
+
+		$connected_proxy_url->set( 'https://example.com' );
+
+		$this->assertEquals(
+			base64_encode( 'https://example.com/' ),
+			$this->options->get( Connected_Proxy_URL::OPTION ),
+			'The `set()` method should store the URL as a base64-encoded string, with a trailing slash.'
+		);
+	}
+
+	public function test_get__decodes_the_stored_url() {
+		$connected_proxy_url = new Connected_Proxy_URL( $this->options );
+		$connected_proxy_url->register();
+
+		$connected_proxy_url->set( 'https://example.com' );
+
+		$this->assertEquals( 'https://example.com/', $connected_proxy_url->get(), 'The `get()` method should return the URL in plain text.' );
+	}
+
+	public function test_get__returns_false_when_not_set() {
+		$connected_proxy_url = new Connected_Proxy_URL( $this->options );
+		$connected_proxy_url->register();
+
+		$this->assertFalse( $connected_proxy_url->get(), 'The `get()` method should return FALSE when no value exists.' );
+	}
+
+	public function test_get__returns_false_for_a_value_that_fails_to_decode() {
+		$connected_proxy_url = new Connected_Proxy_URL( $this->options );
+		$connected_proxy_url->register();
+
+		$this->options->set( Connected_Proxy_URL::OPTION, 'not*a*valid*value' );
+
+		$this->assertFalse( $connected_proxy_url->get(), 'The `get()` method should return FALSE for a stored value that fails to decode.' );
+	}
+
 	/**
 	 * @inheritDoc
 	 */
diff --git a/tests/phpunit/integration/Core/Util/Migration_N_E_X_TTest.php b/tests/phpunit/integration/Core/Util/Migration_N_E_X_TTest.php
new file mode 100644
index 00000000000..32920280d14
--- /dev/null
+++ b/tests/phpunit/integration/Core/Util/Migration_N_E_X_TTest.php
@@ -0,0 +1,186 @@
+<?php
+/**
+ * \Google\Site_Kit\Tests\Core\Util\Migration_N_E_X_TTest
+ *
+ * @package   Google\Site_Kit\Tests\Core\Util
+ * @copyright 2026 Google LLC
+ * @license   https://www.apache.org/licenses/LICENSE-2.0 Apache License 2.0
+ * @link      https://sitekit.withgoogle.com
+ */
+
+namespace Google\Site_Kit\Tests\Core\Util;
+
+use Google\Site_Kit\Context;
+use Google\Site_Kit\Core\Authentication\Authentication;
+use Google\Site_Kit\Core\Authentication\Connected_Proxy_URL;
+use Google\Site_Kit\Core\Authentication\Disconnected_Reason;
+use Google\Site_Kit\Core\Permissions\Permissions;
+use Google\Site_Kit\Core\Storage\Options;
+use Google\Site_Kit\Core\Storage\User_Options;
+use Google\Site_Kit\Core\Util\Migration_N_E_X_T;
+use Google\Site_Kit\Tests\Fake_Site_Connection_Trait;
+use Google\Site_Kit\Tests\TestCase;
+
+class Migration_N_E_X_TTest extends TestCase {
+
+	use Fake_Site_Connection_Trait;
+
+	protected Context $context;
+	protected Options $options;
+	protected Connected_Proxy_URL $connected_proxy_url;
+
+	public function set_up() {
+		parent::set_up();
+
+		$this->context             = new Context( GOOGLESITEKIT_PLUGIN_MAIN_FILE );
+		$this->options             = new Options( $this->context );
+		$this->connected_proxy_url = new Connected_Proxy_URL( $this->options );
+
+		// Drop the option, so each test starts from the value it stores itself.
+		$this->options->delete( Connected_Proxy_URL::OPTION );
+
+		$this->delete_db_version();
+	}
+
+	public function get_new_migration_instance() {
+		return new Migration_N_E_X_T(
+			$this->context,
+			$this->options
+		);
+	}
+
+	public function test_register() {
+		$migration = $this->get_new_migration_instance();
+		remove_all_actions( 'admin_init' );
+
+		$migration->register();
+
+		$this->assertNotFalse(
+			has_action( 'admin_init', array( $migration, 'migrate' ) ),
+			'Migration should register migrate on admin_init.'
+		);
+	}
+
+	public function test_migrate__encodes_a_legacy_plain_text_url() {
+		$migration = $this->get_new_migration_instance();
+
+		// Store the option in plain text, the way earlier plugin versions saved it.
+		$this->options->set( Connected_Proxy_URL::OPTION, 'https://example.com/' );
+
+		$migration->migrate();
+
+		$this->assertEquals(
+			base64_encode( 'https://example.com/' ),
+			$this->options->get( Connected_Proxy_URL::OPTION ),
+			'Migration should store the legacy plain text URL encoded.'
+		);
+		$this->assertEquals(
+			'https://example.com/',
+			$this->connected_proxy_url->get(),
+			'The `get()` method should still return the plain text URL after the migration.'
+		);
+	}
+
+	public function test_migrate__keeps_an_already_encoded_url() {
+		$migration = $this->get_new_migration_instance();
+
+		$this->connected_proxy_url->set( 'https://example.com' );
+		$stored_connected_url = $this->options->get( Connected_Proxy_URL::OPTION );
+
+		$migration->migrate();
+
+		$this->assertSame(
+			$stored_connected_url,
+			$this->options->get( Connected_Proxy_URL::OPTION ),
+			'Migration should keep an already encoded value unchanged.'
+		);
+	}
+
+	public function test_migrate__runs_before_the_connected_proxy_url_check() {
+		remove_all_actions( 'admin_init' );
+
+		$user_id = $this->factory()->user->create( array( 'role' => 'administrator' ) );
+		wp_set_current_user( $user_id );
+
+		$user_options = new User_Options( $this->context );
+
+		// Register in the order the plugin does. The connected proxy URL check
+		// runs at a later priority, so the migration encodes the stored value
+		// before the check reads it.
+		$authentication = new Authentication( $this->context, $this->options, $user_options );
+		$authentication->register();
+		$this->get_new_migration_instance()->register();
+
+		// Store the home URL in plain text, the way earlier plugin versions saved it.
+		$this->options->set( Connected_Proxy_URL::OPTION, $this->context->get_canonical_home_url() );
+
+		// Emulate credentials.
+		$this->fake_proxy_site_connection();
+
+		// Emulate OAuth access token.
+		$authentication->get_oauth_client()->set_token( array( 'access_token' => 'valid-auth-token' ) );
+
+		// Grant the administrator the Permissions::SETUP capability regardless
+		// of authentication.
+		add_filter(
+			'user_has_cap',
+			function ( $caps ) {
+				$caps[ Permissions::SETUP ] = true;
+				return $caps;
+			}
+		);
+
+		do_action( 'admin_init' );
+
+		$this->assertEquals(
+			base64_encode( trailingslashit( $this->context->get_canonical_home_url() ) ),
+			$this->options->get( Connected_Proxy_URL::OPTION ),
+			'Migration should encode the plain text URL on admin_init.'
+		);
+		$this->assertFalse(
+			$user_options->get( Disconnected_Reason::OPTION ),
+			'Site Kit should stay connected when the migration encodes the URL the site still runs on.'
+		);
+	}
+
+	public function test_migrate__skips_when_the_option_is_missing() {
+		$migration = $this->get_new_migration_instance();
+
+		$migration->migrate();
+
+		$this->assertOptionNotExists( Connected_Proxy_URL::OPTION );
+	}
+
+	public function test_migrate__sets_db_version() {
+		$migration = $this->get_new_migration_instance();
+
+		$migration->migrate();
+
+		$this->assertEquals( 'n.e.x.t', $this->get_db_version(), "Database version should update to the migration's target version after the migration runs." );
+	}
+
+	public function test_migrate__skips_when_the_db_version_is_current() {
+		$migration = $this->get_new_migration_instance();
+
+		$this->options->set( Migration_N_E_X_T::DB_VERSION_OPTION, Migration_N_E_X_T::DB_VERSION );
+
+		// Store the option in plain text, the way earlier plugin versions saved it.
+		$this->options->set( Connected_Proxy_URL::OPTION, 'https://example.com/' );
+
+		$migration->migrate();
+
+		$this->assertEquals(
+			'https://example.com/',
+			$this->options->get( Connected_Proxy_URL::OPTION ),
+			'Migration should leave the stored value alone when the database version already matches its target.'
+		);
+	}
+
+	protected function get_db_version() {
+		return $this->options->get( Migration_N_E_X_T::DB_VERSION_OPTION );
+	}
+
+	protected function delete_db_version() {
+		$this->options->delete( Migration_N_E_X_T::DB_VERSION_OPTION );
+	}
+}