Setting a timeout on the Brevo PHP SDK v4 client with Guzzle installed emits: User Warning: Timeout option is not supported for the current PSR-18 client (GuzzleHttp\Client). Use Guzzle or Symfony HttpClient for timeout support. The cause is in src/Core/Client/RetryDecoratingClient.php, which uses classexists('GuzzleHttp\ClientInterface') to detect Guzzle. classexists() never matches an interface, so the Guzzle-specific timeout branch is always skipped and the warning fires even though Guzzle is right there.