Я получаю 401 на Guzzle 4.2 и такая же настройка работает на Почтальоне. Код ниже.

// Create a client with a base URL
    $client = new GuzzleHttp\Client(['base_url' => 'cloud.feedly.com/v3/streams/contents?streamId=user/user-id/category/global.all&count=1']);

    // Send a request to https://github.com/notifications
    $response = $client->get();

    //Auth
   $response->addHeader('Authorization', "auth-code");


    //send
    $r = $response->send();

   dd($r->json());

Ошибка:

GuzzleHttp \ Exception \ ClientException (401) 
Client error response [url] cloud.feedly.com/v3/streams/contents?streamId=user/user-id/global.all&count=1 [status code] 401 [reason phrase] Unauthorized