// Initiate each request but do not block $promises = [ 'image' => $client->getAsync('/image'), 'png' => $client->getAsync('/image/png'), 'jpeg' => $client->getAsync('/image/jpeg'), 'webp' => $client->getAsync('/image/webp') ]; // Wait on all of the requests to complete. $results = Promise\unwrap($promises); // You can access each result using the key provided to the unwrap // function. echo $results['image']->getHeader('Content-Length'); echo $results['png']->getHeader('Content-Length');