Guzzle is part of Drupal 8 as Drupal::httpClient();

Drupal - httpClient Example

<?php
// See https://jobs.github.com/api for documentation.

$client = \Drupal::httpClient();
$params = [
  'query' => [
    'description' => 'laravel',
    'full_time' => true,
  ]
];
$request = $client->get('https://jobs.github.com/positions.json', $params);
$response = $request->getBody()->getContents();
$jobs = json_decode($response);
foreach ($jobs as $job) {
 print_r($job->company . ' - ' . $job->location);
}