diff --git a/tests/Support/Helper/KitAPI.php b/tests/Support/Helper/KitAPI.php
index 51f00d494..b331e0f28 100644
--- a/tests/Support/Helper/KitAPI.php
+++ b/tests/Support/Helper/KitAPI.php
@@ -9,6 +9,91 @@
  */
 class KitAPI extends \Codeception\Module
 {
+	/**
+	 * Installs the Kit API recorder mu-plugin, and clears any previously recorded
+	 * requests, before each test runs.
+	 *
+	 * @since   3.4.1
+	 *
+	 * @param   \Codeception\TestInterface $test   Test.
+	 */
+	public function _before(\Codeception\TestInterface $test) // phpcs:ignore PSR2.Methods.MethodDeclaration.Underscore, Generic.CodeAnalysis.UnusedFunctionParameter
+	{
+		$this->getModule('lucatume\WPBrowser\Module\WPFilesystem')->haveMuPlugin(
+			'kit-api-recorder.php',
+			(string) file_get_contents(__DIR__ . '/../mu-plugins/kit-api-recorder.php') // phpcs:ignore WordPress.WP.AlternativeFunctions.file_get_contents_file_get_contents
+		);
+
+		$this->getModule('lucatume\WPBrowser\Module\WPDb')->haveOptionInDatabase('kit_api_log', []);
+	}
+
+	/**
+	 * Returns the Kit API requests the Plugin made during this test, optionally
+	 * filtered by method, path and email address.
+	 *
+	 * @since   3.4.1
+	 *
+	 * @param   EndToEndTester $I              EndToEndTester.
+	 * @param   string         $method         HTTP method (GET,POST,PUT,DELETE).
+	 * @param   string         $path           Request path, excluding the API version e.g. `subscribers`.
+	 * @param   bool|string    $emailAddress   Email address in the request body.
+	 * @return  array
+	 */
+	public function grabKitAPIRequests($I, $method = false, $path = false, $emailAddress = false)
+	{
+		$log = $I->grabOptionFromDatabase('kit_api_log');
+
+		if ( ! is_array($log)) {
+			return [];
+		}
+
+		return array_values(
+			array_filter(
+				$log,
+				function ($request) use ($method, $path, $emailAddress) {
+					if ($method && $request['method'] !== $method) {
+						return false;
+					}
+					if ($path && $request['path'] !== $path) {
+						return false;
+					}
+					if ($emailAddress && ( ! array_key_exists('email_address', $request['body']) || $request['body']['email_address'] !== $emailAddress )) {
+						return false;
+					}
+
+					return true;
+				}
+			)
+		);
+	}
+
+	/**
+	 * Returns the first Kit API request the Plugin made during this test that matches
+	 * the given method, path and email address, waiting for it to be made.
+	 *
+	 * @since   3.4.1
+	 *
+	 * @param   EndToEndTester $I              EndToEndTester.
+	 * @param   string         $method         HTTP method (GET,POST,PUT,DELETE).
+	 * @param   string         $path           Request path, excluding the API version e.g. `subscribers`.
+	 * @param   bool|string    $emailAddress   Email address in the request body.
+	 * @return  bool|array
+	 */
+	public function grabKitAPIRequest($I, $method, $path, $emailAddress = false)
+	{
+		// The request is made by WordPress when the form is submitted, which may not have
+		// completed when this is called e.g. when a form submits using AJAX.
+		return $this->retryUntil(
+			function () use ($I, $method, $path, $emailAddress) {
+				$requests = $this->grabKitAPIRequests($I, $method, $path, $emailAddress);
+
+				return count($requests) ? $requests[0] : false;
+			},
+			10,
+			1
+		);
+	}
+
 	/**
 	 * Returns an encoded `state` parameter compatible with OAuth.
 	 *
@@ -42,6 +127,12 @@ public function apiEncodeState($returnTo, $clientID)
 	/**
 	 * Check the given email address exists as a subscriber.
 	 *
+	 * The Plugin's request to create the subscriber is used to determine the subscriber ID,
+	 * as querying the API by email address is subject to eventual consistency. Querying by
+	 * subscriber ID returns strongly consistent results.
+	 *
+	 * @see     https://developers.kit.com/api-reference/eventual-consistency
+	 *
 	 * @param   EndToEndTester $I              EndToEndTester.
 	 * @param   string         $emailAddress   Email Address.
 	 * @param   string         $firstName      First Name (false = don't check name matches).
@@ -49,42 +140,33 @@ public function apiEncodeState($returnTo, $clientID)
 	 */
 	public function apiCheckSubscriberExists($I, $emailAddress, $firstName = false)
 	{
-		// Wait for the API to update.
-		$I->wait(3);
+		// Get the request the Plugin made to create the subscriber.
+		$request = $this->grabKitAPIRequest($I, 'POST', 'subscribers', $emailAddress);
 
-		// Retry the API request as sometimes there's a lag before the subscriber is queryable via the API.
-		$results = $this->retryUntil(
-			function () use ($emailAddress) {
-				$results = $this->apiRequest(
-					'subscribers',
-					'GET',
-					[
-						'email_address'       => $emailAddress,
-						'include_total_count' => true,
-
-						// Check all subscriber states.
-						'status'              => 'all',
-					]
-				);
-
-				// Return the results only if a subscriber was found, so
-				// retryUntil() will keep trying otherwise.
-				return ( $results['pagination']['total_count'] > 0 ) ? $results : false;
-			}
+		// Check the Plugin created the subscriber.
+		$I->assertNotFalse(
+			$request,
+			sprintf('The Plugin did not send a request to create the subscriber %s.', $emailAddress)
 		);
+		$I->assertLessThan(
+			300,
+			$request['code'],
+			sprintf('The API returned a %s response when the Plugin created the subscriber %s.', $request['code'], $emailAddress)
+		);
+
+		// Fetch the subscriber by their ID, which returns strongly consistent results.
+		$results = $this->apiRequest('subscribers/' . $request['response']['subscriber']['id'], 'GET');
 
-		// Check at least one subscriber was returned and it matches the email address.
-		$I->assertNotFalse($results);
-		$I->assertGreaterThan(0, $results['pagination']['total_count']);
-		$I->assertEquals($emailAddress, $results['subscribers'][0]['email_address']);
+		// Check the subscriber matches the email address.
+		$I->assertEquals($emailAddress, $results['subscriber']['email_address']);
 
 		// If defined, check that the name matches for the subscriber.
 		if ($firstName) {
-			$I->assertEquals($firstName, $results['subscribers'][0]['first_name']);
+			$I->assertEquals($firstName, $results['subscriber']['first_name']);
 		}
 
-		// Return subscriber ID.
-		return $results['subscribers'][0];
+		// Return subscriber.
+		return $results['subscriber'];
 	}
 
 	/**
@@ -99,27 +181,35 @@ function () use ($emailAddress) {
 	 */
 	public function apiCheckSubscriberHasForm($I, $subscriberID, $formID, $referrer = false)
 	{
-		// Run request.
-		$results = $this->apiRequest(
-			'forms/' . $formID . '/subscribers',
-			'GET',
-			[
-				// Check all subscriber states.
-				'status' => 'all',
-			]
-		);
+		// Wait for the subscriber to be assigned to the form, as list endpoints are eventually consistent.
+		$subscriber = $this->retryUntil(
+			function () use ($subscriberID, $formID) {
+				$results = $this->apiRequest(
+					'forms/' . $formID . '/subscribers',
+					'GET',
+					[
+						// Check all subscriber states.
+						'status' => 'all',
+					]
+				);
 
-		// Iterate through subscribers.
-		$subscriberHasForm = false;
-		foreach ($results['subscribers'] as $subscriber) {
-			if ($subscriber['id'] === $subscriberID) {
-				$subscriberHasForm = true;
-				break;
+				// Return the subscriber only if they're assigned to the form, so
+				// retryUntil() will keep trying otherwise.
+				foreach ($results['subscribers'] as $subscriber) {
+					if ( (int) $subscriber['id'] === (int) $subscriberID) {
+						return $subscriber;
+					}
+				}
+
+				return false;
 			}
-		}
+		);
 
-		// Assert if the subscriber has the form.
-		$this->assertTrue($subscriberHasForm);
+		// Assert the subscriber has the form.
+		$I->assertNotFalse(
+			$subscriber,
+			sprintf('Subscriber %s was not assigned to Form %s in time.', $subscriberID, $formID)
+		);
 
 		// If a referrer is specified, assert it matches the subscriber's referrer now.
 		if ($referrer) {
@@ -138,26 +228,34 @@ public function apiCheckSubscriberHasForm($I, $subscriberID, $formID, $referrer
 	 */
 	public function apiCheckSubscriberHasSequence($I, $subscriberID, $sequenceID)
 	{
-		// Run request.
-		$results = $this->apiRequest(
-			'sequences/' . $sequenceID . '/subscribers',
-			'GET',
-			[
-				'status' => 'all',
-			]
-		);
+		// Wait for the subscriber to be assigned to the sequence, as list endpoints are eventually consistent.
+		$subscriber = $this->retryUntil(
+			function () use ($subscriberID, $sequenceID) {
+				$results = $this->apiRequest(
+					'sequences/' . $sequenceID . '/subscribers',
+					'GET',
+					[
+						'status' => 'all',
+					]
+				);
 
-		// Iterate through subscribers.
-		$subscriberHasSequence = false;
-		foreach ($results['subscribers'] as $subscriber) {
-			if ($subscriber['id'] === $subscriberID) {
-				$subscriberHasSequence = true;
-				break;
+				// Return the subscriber only if they're assigned to the sequence, so
+				// retryUntil() will keep trying otherwise.
+				foreach ($results['subscribers'] as $subscriber) {
+					if ( (int) $subscriber['id'] === (int) $subscriberID) {
+						return $subscriber;
+					}
+				}
+
+				return false;
 			}
-		}
+		);
 
-		// Assert if the subscriber has the sequence.
-		$this->assertTrue($subscriberHasSequence);
+		// Assert the subscriber has the sequence.
+		$I->assertNotFalse(
+			$subscriber,
+			sprintf('Subscriber %s was not assigned to Sequence %s in time.', $subscriberID, $sequenceID)
+		);
 	}
 
 	/**
@@ -169,14 +267,31 @@ public function apiCheckSubscriberHasSequence($I, $subscriberID, $sequenceID)
 	 */
 	public function apiCheckSubscriberHasTag($I, $subscriberID, $tagID)
 	{
-		// Run request.
-		$results = $this->apiRequest(
-			'subscribers/' . $subscriberID . '/tags',
-			'GET'
+		// Wait for the tag to be assigned to the subscriber, as list endpoints are eventually consistent.
+		$tag = $this->retryUntil(
+			function () use ($subscriberID, $tagID) {
+				$results = $this->apiRequest(
+					'subscribers/' . $subscriberID . '/tags',
+					'GET'
+				);
+
+				// Return the tag only if it's assigned to the subscriber, so
+				// retryUntil() will keep trying otherwise.
+				foreach ($results['tags'] as $tag) {
+					if ( (int) $tag['id'] === (int) $tagID) {
+						return $tag;
+					}
+				}
+
+				return false;
+			}
 		);
 
-		// Confirm the tag has been assigned to the subscriber.
-		$I->assertEquals($tagID, $results['tags'][0]['id']);
+		// Assert the subscriber has the tag.
+		$I->assertNotFalse(
+			$tag,
+			sprintf('Subscriber %s was not assigned Tag %s in time.', $subscriberID, $tagID)
+		);
 	}
 
 	/**
@@ -316,8 +431,8 @@ public function apiRequest($endpoint, $method = 'GET', $params = array())
 					[
 						'headers' => [
 							'Authorization' => 'Bearer ' . $_ENV['CONVERTKIT_OAUTH_ACCESS_TOKEN'],
-							'timeout'       => 5,
 						],
+						'timeout' => 5,
 					]
 				);
 				break;
@@ -331,8 +446,8 @@ public function apiRequest($endpoint, $method = 'GET', $params = array())
 							'Accept'        => 'application/json',
 							'Content-Type'  => 'application/json; charset=utf-8',
 							'Authorization' => 'Bearer ' . $_ENV['CONVERTKIT_OAUTH_ACCESS_TOKEN'],
-							'timeout'       => 5,
 						],
+						'timeout' => 5,
 						'body'    => (string) json_encode($params), // phpcs:ignore WordPress.WP.AlternativeFunctions
 					]
 				);
diff --git a/tests/Support/mu-plugins/kit-api-recorder.php b/tests/Support/mu-plugins/kit-api-recorder.php
new file mode 100644
index 000000000..ad06f5dd2
--- /dev/null
+++ b/tests/Support/mu-plugins/kit-api-recorder.php
@@ -0,0 +1,53 @@
+<?php
+/**
+ * Plugin Name: Kit API Recorder
+ * Description: Records Kit API requests and responses in an option, for end to end tests to assert against.
+ *
+ * @package ConvertKit
+ * @author ConvertKit
+ */
+
+// Record Kit API requests and responses.
+add_action(
+	'http_api_debug',
+	function ( $response, $context, $transport, $parsed_args, $url ) { // phpcs:ignore Generic.CodeAnalysis.UnusedFunctionParameter
+
+		// Bail if this isn't a request to the Kit API.
+		if ( strpos( $url, 'https://api.kit.com/' ) !== 0 ) {
+			return;
+		}
+
+		// Build the request path, excluding the API version and any query parameters.
+		$path  = (string) wp_parse_url( $url, PHP_URL_PATH );
+		$path  = ltrim( str_replace( '/v4/', '', $path ), '/' );
+		$query = array();
+		parse_str( (string) wp_parse_url( $url, PHP_URL_QUERY ), $query );
+
+		// Decode the request body, which is JSON encoded for POST, PUT and DELETE requests.
+		$body = array();
+		if ( ! empty( $parsed_args['body'] ) ) {
+			$body = is_string( $parsed_args['body'] ) ? json_decode( $parsed_args['body'], true ) : $parsed_args['body'];
+		}
+
+		// Fetch the existing log.
+		$log = get_option( 'kit_api_log', array() );
+		if ( ! is_array( $log ) ) {
+			$log = array();
+		}
+
+		// Append this request and its response to the log.
+		$log[] = array(
+			'method'   => isset( $parsed_args['method'] ) ? $parsed_args['method'] : 'GET',
+			'path'     => $path,
+			'query'    => $query,
+			'body'     => is_array( $body ) ? $body : array(),
+			'code'     => is_wp_error( $response ) ? 0 : (int) wp_remote_retrieve_response_code( $response ),
+			'error'    => is_wp_error( $response ) ? $response->get_error_message() : '',
+			'response' => is_wp_error( $response ) ? array() : (array) json_decode( wp_remote_retrieve_body( $response ), true ),
+		);
+
+		update_option( 'kit_api_log', $log, false );
+	},
+	10,
+	5
+);