diff --git a/assets/css/main.css b/assets/css/main.css
new file mode 100644
index 00000000..e69de29b
diff --git a/inc/admin-interface.php b/inc/admin-interface.php
index be6feae2..8e66f97a 100644
--- a/inc/admin-interface.php
+++ b/inc/admin-interface.php
@@ -34,6 +34,8 @@ function bootstrap() {
 
 	add_filter( 'site_status_tests', __NAMESPACE__ . '\\default_cache_max_age_test' );
 	add_action( 'update_option_pantheon-cache', __NAMESPACE__ . '\\clear_max_age_compare_cache' );
+	add_action( 'admin_init', __NAMESPACE__ . '\\set_max_age_to_default' );
+	add_action( 'admin_notices', __NAMESPACE__ . '\\max_age_updated_admin_notice' );
 }
 
 /**
@@ -47,8 +49,9 @@ function admin_notice_no_mu_plugin() {
 	 * Allow disabling the admin notice.
 	 *
 	 * @param bool $disable_admin_notices Whether to disable the admin notice.
+	 * @param string $callback The name of the current callback function.
 	 */
-	if ( apply_filters( 'pantheon_apc_disable_admin_notices', false ) ) {
+	if ( apply_filters( 'pantheon_apc_disable_admin_notices', false, __FUNCTION__ ) ) {
 		return;
 	}
 
@@ -71,7 +74,7 @@ function admin_notice_no_mu_plugin() {
 function admin_notice_old_mu_plugin() {
 	$current_screen = get_current_screen();
 
-	if ( apply_filters( 'pantheon_apc_disable_admin_notices', false ) || 'settings_page_pantheon-cache' !== $current_screen->id ) {
+	if ( apply_filters( 'pantheon_apc_disable_admin_notices', false, __FUNCTION__ ) || 'settings_page_pantheon-cache' !== $current_screen->id ) {
 		return;
 	}
 
@@ -109,7 +112,7 @@ function admin_notice_old_mu_plugin() {
 function admin_notice_maybe_recommend_higher_max_age() {
 	$current_screen = get_current_screen();
 
-	if ( apply_filters( 'pantheon_apc_disable_admin_notices', false ) || 'settings_page_pantheon-cache' !== $current_screen->id ) {
+	if ( apply_filters( 'pantheon_apc_disable_admin_notices', false, __FUNCTION__ ) || 'settings_page_pantheon-cache' !== $current_screen->id ) {
 		return;
 	}
 
@@ -317,3 +320,86 @@ function test_cache_max_age() {
 function clear_max_age_compare_cache() {
 	delete_transient( 'papc_max_age_compare' );
 }
+
+/**
+ * Set the default_ttl from the mu-plugin to WEEK_IN_SECONDS if it was saved as 600 seconds.
+ *
+ * @since 2.0.0
+ * @return bool
+ */
+function set_max_age_to_default() {
+	$pantheon_cache = get_option( 'pantheon-cache', [] );
+	$pantheon_max_age_updated = get_option( 'pantheon_max_age_updated', false );
+
+	// If we've already done this, bail.
+	if ( $pantheon_max_age_updated ) {
+		return;
+	}
+
+	// If nothing is saved, bail. The default is used automatically.
+	if ( ! isset( $pantheon_cache['default_ttl'] ) ) {
+		return;
+	}
+
+	// Everything beyond this point assumes the max age has been set manually or will be set to the default.
+	update_option( 'pantheon_max_age_updated', true );
+
+	// If the default_ttl is not 600, bail.
+	if ( 600 !== $pantheon_cache['default_ttl'] ) {
+		return;
+	}
+
+	// Set the max age. At this point, we should only be here if it was set to 600. We're using the filter here in case someone has overridden the default.
+	$pantheon_cache['default_ttl'] = apply_filters( 'pantheon_cache_default_max_age', WEEK_IN_SECONDS );
+
+	// Update the option and set the max_age_updated flag and show the admin notice.
+	update_option( 'pantheon-cache', $pantheon_cache );
+}
+
+/**
+ * Display an admin notice if the max-age was updated.
+ *
+ * @since 2.0.0
+ * @return void
+ */
+function max_age_updated_admin_notice() {
+	// Check if notices should be disabled. This includes if the user is using a version of WordPress that does not support wp_admin_notice.
+	if ( apply_filters( 'pantheon_apc_disable_admin_notices', false, __FUNCTION__ ) ) {
+		return;
+	}
+
+	// Can the user manage options? If not, don't show the notice.
+	if ( ! current_user_can( 'manage_options' ) ) {
+		return;
+	}
+
+	// Check user meta to see if this user has seen this notice before.
+	$current_user_id = get_current_user_id();
+	$dismissed = get_user_meta( $current_user_id, 'pantheon_max_age_updated_notice', true );
+	if ( $dismissed ) {
+		return;
+	}
+
+	// Check if the max-age was updated.
+	$max_age_updated = get_option( 'pantheon_max_age_updated', false );
+	if ( ! $max_age_updated ) {
+		return;
+	}
+
+	// If we got here, this is the _first time_ this user has seen this notice since the option was updated. Show the notice and update the user meta.
+	wp_admin_notice(
+		sprintf(
+			// translators: %1$s is the humanized max-age, %2$d is a link to the Pantheon documentation.
+			__( 'The Pantheon GCDN cache max-age has been updated. The previous value was 10 minutes. The new value is %1$s. For more information, refer to the <a href="%2$s">Pantheon documentation</a>.', 'pantheon-advanced-page-cache' ),
+			humanized_max_age(),
+			'https://docs.pantheon.io/guides/wordpress-configurations/wordpress-cache-plugin'
+		),
+		[
+			'type' => 'info',
+			'dismissible' => false,
+		]
+	);
+
+	// Update the user meta to prevent this notice from showing again after they've seen it once.
+	update_user_meta( $current_user_id, 'pantheon_max_age_updated_notice', true );
+}
diff --git a/tests/behat/admin-interface.feature b/tests/behat/admin-interface.feature
index 044f877f..7221b623 100644
--- a/tests/behat/admin-interface.feature
+++ b/tests/behat/admin-interface.feature
@@ -3,6 +3,14 @@ Feature: Adjust the Default Max Age setting
 Background:
 	Given I log in as an admin
 
+Scenario: Set max-age to 600 and auto-update to the default value
+	When I go to "/wp-admin/options-general.php?page=pantheon-cache"
+	And I fill in "pantheon-cache[default_ttl]" with "600"
+	And I press "Save Changes"
+	Then I should see "The Pantheon GCDN cache max-age has been updated. The previous value was 10 minutes. The new value is 1 week."
+	When I go to "/wp-admin/options-general.php?page=pantheon-cache"
+	Then the "pantheon-cache[default_ttl]" field should contain "604800"
+
 Scenario: Change the cache max age
 	When I go to "/wp-admin/options-general.php?page=pantheon-cache"
 	And I fill in "pantheon-cache[default_ttl]" with "300"
diff --git a/tests/phpunit/test-admin-interface.php b/tests/phpunit/test-admin-interface.php
index 8da3f335..4f91f469 100644
--- a/tests/phpunit/test-admin-interface.php
+++ b/tests/phpunit/test-admin-interface.php
@@ -25,6 +25,7 @@ public function setUp(): void {
 	public function tearDown(): void {
 		parent::tearDown();
 		delete_option( 'pantheon-cache' );
+		delete_option( 'pantheon_max_age_updated' );
 		delete_transient( 'papc_max_age_compare' );
 	}
 
@@ -157,4 +158,117 @@ public function delete_transient_on_option_update_provider() {
 		];
 	}
 
+	/**
+	 * Test running set_max_age_to_default when no option has been set.
+	 */
+	public function test_set_max_age_to_default_start() {
+		// Default start state.
+		delete_option( 'pantheon-cache' );
+		set_max_age_to_default();
+		$pantheon_cache = get_option( 'pantheon-cache' );
+		$max_age_updated = get_option( 'pantheon_max_age_updated' );
+		$this->assertFalse( isset( $pantheon_cache['default_ttl'] ), 'The default_ttl option should not be set.' );
+		$this->assertFalse( $max_age_updated, 'The max age updated option should not be set.');
+	}
+
+	/**
+	 * Test running set_max_age_to_default when the default_ttl is 600.
+	 */
+	public function test_set_max_age_to_default_600() {
+		// Cache max-age set to 600 and we haven't updated it since the notice.
+		$pantheon_cache = [];
+		$pantheon_cache['default_ttl'] = 600;
+		update_option( 'pantheon-cache', $pantheon_cache );
+		$pantheon_cache = get_option( 'pantheon-cache' );
+		// Validate that the option was set correctly. We'll only check this once.
+		$this->assertEquals( 600, $pantheon_cache['default_ttl'], 'The default_ttl option should be set to 600.' );
+		set_max_age_to_default();
+		$pantheon_cache = get_option( 'pantheon-cache' );
+		$max_age_updated = get_option( 'pantheon_max_age_updated' );
+		$this->assertEquals( WEEK_IN_SECONDS, $pantheon_cache['default_ttl'], 'The default_ttl option should be set to 1 week.');
+		$this->assertTrue( $max_age_updated, 'The max age updated option should be true.');
+	}
+
+	/**
+	 * Test running set_max_age_to_default when the default_ttl was manually reset to 600.
+	 */
+	public function test_set_max_age_to_default_600_reset() {
+		// Cache max-age set to 600 and we have updated it since the notice.
+		$pantheon_cache = [];
+		$pantheon_cache['default_ttl'] = 600;
+		update_option( 'pantheon-cache', $pantheon_cache );
+		update_option( 'pantheon_max_age_updated', true );
+		set_max_age_to_default();
+		$pantheon_cache = get_option( 'pantheon-cache' );
+		$this->assertEquals( 600, $pantheon_cache['default_ttl'], 'The default_ttl option should be set to 600.' );
+	}
+
+	/**
+	 * Test running set_max_age_to_default when the default_ttl is 432000.
+	 */
+	public function test_set_max_age_to_default_432000() {
+		// Cache max-age set to anything else. We shouldn't ever see the notice.
+		delete_option( 'pantheon_max_age_updated' );
+		$pantheon_cache = [];
+		$pantheon_cache['default_ttl'] = 432000;
+		update_option( 'pantheon-cache', $pantheon_cache );
+		set_max_age_to_default();
+		$pantheon_cache = get_option( 'pantheon-cache' );
+		$max_age_updated = get_option( 'pantheon_max_age_updated' );
+		$this->assertEquals( 432000, $pantheon_cache['default_ttl'], 'The default_ttl option should be set to 432000.' );
+		$this->assertTrue( $max_age_updated, 'The max age updated option should be true.');
+	}
+
+	/**
+	 * Test running set_max_age_to_default when the default_ttl is 600 and a filter is set.
+	 */
+	public function test_set_max_age_to_default_600_filter() {
+		// Use the filter to override the default. If a site had 600 set, we should still update it to the filtered value.
+		add_filter( 'pantheon_cache_default_max_age', function() {
+			return 3 * DAY_IN_SECONDS;
+		} );
+		$pantheon_cache = [];
+		$pantheon_cache['default_ttl'] = 600;
+		update_option( 'pantheon-cache', $pantheon_cache );
+		set_max_age_to_default();
+		$pantheon_cache = [];
+		$pantheon_cache = get_option( 'pantheon-cache' );
+		$max_age_updated = get_option( 'pantheon_max_age_updated' );
+		$this->assertEquals( 3 * DAY_IN_SECONDS, $pantheon_cache['default_ttl'], 'The default_ttl option should be set to 3 days (the filtered value).' );
+		$this->assertTrue( $max_age_updated, 'The max age updated option should be true.');
+	}
+
+	/**
+	 * Test the admin notice for the max age being updated.
+	 */
+	function test_max_age_updated_admin_notice() {
+		// Switch to admin.
+		wp_set_current_user( 1 );
+
+		// We're testing notices but we don't want to display the "no mu plugin" notice.
+		add_filter( 'pantheon_apc_disable_admin_notices', function( $disable_notices, $callback ) {
+			if ( $callback === __NAMESPACE__ . '\\admin_notice_no_mu_plugin' ) {
+				return true;
+			}
+			return $disable_notices;
+		}, 10, 2 );
+
+		$current_user_id = get_current_user_id();
+
+		// Reset everything to start.
+		delete_option( 'pantheon-cache' );
+		delete_user_meta( $current_user_id, 'pantheon_max_age_updated_notice' );
+
+		// Make sure the option says we've updated the max age. We're checking the notice, not the option.
+		update_option( 'pantheon_max_age_updated', true );
+
+		ob_start();
+		max_age_updated_admin_notice();
+		$notice = ob_get_clean();
+
+		// The notice that we're catching should be the one that the max-age was updated.
+		$this->assertStringContainsString( 'The Pantheon GCDN cache max-age has been updated. The previous value was 10 minutes. The new value is 1 week.', $notice );
+		// The user meta should have been updated in the process.
+		$this->assertEquals( 1, get_user_meta( $current_user_id, 'pantheon_max_age_updated_notice', true ) );
+	}
 }