diff --git a/lib/Checkout/AbstractCheckoutSdkBuilder.php b/lib/Checkout/AbstractCheckoutSdkBuilder.php
index 2769b4f..738bfbd 100644
--- a/lib/Checkout/AbstractCheckoutSdkBuilder.php
+++ b/lib/Checkout/AbstractCheckoutSdkBuilder.php
@@ -13,12 +13,14 @@ abstract class AbstractCheckoutSdkBuilder
     protected $environmentSubdomain;
     protected $httpClientBuilder;
     protected $logger;
+    protected $enableTelemetry;
 
     public function __construct()
     {
         $this->environment = Environment::sandbox();
         $this->httpClientBuilder = new DefaultHttpClientBuilder([]);
         $this->setDefaultLogger();
+        $this->enableTelemetry = true;
     }
 
     /**
@@ -50,6 +52,15 @@ public function httpClientBuilder(HttpClientBuilderInterface $httpClientBuilder)
         $this->httpClientBuilder = $httpClientBuilder;
         return $this;
     }
+    /**
+     * @param bool $enableTelemetry
+     * @return $this
+     */
+    public function enableTelemetry($enableTelemetry)
+    {
+        $this->enableTelemetry = $enableTelemetry;
+        return $this;
+    }
 
     /**
      * @param LoggerInterface $logger
@@ -70,7 +81,8 @@ protected function getCheckoutConfiguration()
             $this->getSdkCredentials(),
             $this->environment,
             $this->httpClientBuilder,
-            $this->logger
+            $this->logger,
+            $this->enableTelemetry
         );
     }
 
diff --git a/lib/Checkout/ApiClient.php b/lib/Checkout/ApiClient.php
index b476279..18e3ddf 100644
--- a/lib/Checkout/ApiClient.php
+++ b/lib/Checkout/ApiClient.php
@@ -3,7 +3,9 @@
 namespace Checkout;
 
 use Checkout\Common\AbstractQueryFilter;
+use Checkout\Common\RequestMetrics;
 use Checkout\Files\FileRequest;
+use Checkout\Common\TelemetryQueue;
 use Exception;
 use GuzzleHttp\Exception\RequestException;
 use GuzzleHttp\Psr7\Response;
@@ -21,6 +23,10 @@ class ApiClient
 
     private $baseUri;
 
+    private $enableTelemetry;
+
+    private $requestMetricsQueue;
+
     public function __construct(CheckoutConfiguration $configuration, $baseUri = null)
     {
         $this->configuration = $configuration;
@@ -28,6 +34,8 @@ public function __construct(CheckoutConfiguration $configuration, $baseUri = nul
         $this->jsonSerializer = new JsonSerializer();
         $this->logger = $this->configuration->getLogger();
         $this->baseUri = $baseUri != null ? $baseUri : $this->configuration->getEnvironment()->getBaseUri();
+        $this->enableTelemetry = $this->configuration->isEnableTelemetry();
+        $this->requestMetricsQueue = new TelemetryQueue();
     }
 
     /**
@@ -133,31 +141,49 @@ public function submitFileFilesApi($path, FileRequest $fileRequest, SdkAuthoriza
     }
 
     /**
+     * Summary of handleRequest
+     * @param $method
      * @param $path
-     * @param FileRequest $fileRequest
-     * @param SdkAuthorization $authorization
-     * @param $multipart
+     * @param \Checkout\SdkAuthorization $authorization
+     * @param array $requestOptions
+     * @throws \Checkout\CheckoutApiException
      * @return array
-     * @throws CheckoutApiException
      */
-    private function submit($path, FileRequest $fileRequest, SdkAuthorization $authorization, $multipart)
+    private function handleRequest($method, $path, SdkAuthorization $authorization, array $requestOptions)
     {
         try {
-            $this->logger->info("POST " . $path . " file: " . $fileRequest->file);
-            $headers = $this->getHeaders($authorization, null, null);
-            $response = $this->client->request("POST", $this->getRequestUrl($path), [
-                "verify" => false,
-                "headers" => $headers,
-                "multipart" => [
-                    [
-                        "name" => $multipart,
-                        "contents" => fopen($fileRequest->file, "r")
-                    ],
-                    [
-                        "name" => "purpose",
-                        "contents" => $fileRequest->purpose
-                    ]
-                ]]);
+            $headers = $requestOptions['headers'];
+
+            if ($this->enableTelemetry) {
+                $currentRequestId = uniqid();
+                $lastRequestMetric = new RequestMetrics();
+                $dequeuedMetric = $this->requestMetricsQueue->dequeue();
+
+                
+                if ($dequeuedMetric !== null) {
+                    $lastRequestMetric->requestId = $currentRequestId;
+                    $headers["Cko-Sdk-Telemetry"] = base64_encode(json_encode([
+                        'prev-request-id' => $lastRequestMetric->prevRequestId,
+                        'prev-request-duration' => $lastRequestMetric->prevRequestDuration
+                    ]));
+                }
+                
+                $startTime = microtime(true);
+                $response = $this->client->request($method, $this->getRequestUrl($path), array_merge(
+                    $requestOptions,
+                    ['headers' => $headers]
+                ));
+                $duration = (int)((microtime(true) - $startTime) * 1000);
+                
+                $lastRequestMetric->prevRequestDuration = $duration;
+                $lastRequestMetric->prevRequestId = $currentRequestId;
+                $this->requestMetricsQueue->enqueue($lastRequestMetric);
+            } else {
+                $response = $this->client->request($method, $this->getRequestUrl($path), array_merge(
+                    $requestOptions,
+                    ['headers' => $headers]
+                ));
+            }
             return $this->getResponseContents($response);
         } catch (Exception $e) {
             $this->logger->error($path . " error: " . $e->getMessage());
@@ -168,6 +194,38 @@ private function submit($path, FileRequest $fileRequest, SdkAuthorization $autho
         }
     }
 
+     /**
+     * @param $path
+     * @param FileRequest $fileRequest
+     * @param SdkAuthorization $authorization
+     * @param $multipart
+     * @return array
+     * @throws CheckoutApiException
+     */
+    private function submit($path, FileRequest $fileRequest, SdkAuthorization $authorization, $multipart)
+    {
+    // Keep specific logging in submit
+        $this->logger->info("POST " . $path . " file: " . $fileRequest->file);
+    
+        $headers = $this->getHeaders($authorization, null, null, null);
+        $requestOptions = [
+        "verify" => false,
+        "headers" => $headers,
+        "multipart" => [
+            [
+                "name" => $multipart,
+                "contents" => fopen($fileRequest->file, "r")
+            ],
+            [
+                "name" => "purpose",
+                "contents" => $fileRequest->purpose
+            ]
+        ]
+        ];
+    
+        return $this->handleRequest("POST", $path, $authorization, $requestOptions);
+    }
+
     /**
      * @param string $method
      * @param string $path
@@ -179,22 +237,17 @@ private function submit($path, FileRequest $fileRequest, SdkAuthorization $autho
      */
     private function invoke($method, $path, $body, SdkAuthorization $authorization, $idempotencyKey = null)
     {
-        try {
-            $this->logger->info($method . " " . $path);
-            $headers = $this->getHeaders($authorization, "application/json", $idempotencyKey);
-            $response = $this->client->request($method, $this->getRequestUrl($path), [
-                "verify" => false,
-                "body" => $body,
-                "headers" => $headers
-            ]);
-            return $this->getResponseContents($response);
-        } catch (Exception $e) {
-            $this->logger->error($path . " error: " . $e->getMessage());
-            if ($e instanceof RequestException) {
-                throw CheckoutApiException::from($e);
-            }
-            throw new CheckoutApiException($e);
-        }
+        // Keep specific logging in invoke
+        $this->logger->info($method . " " . $path);
+        
+        $headers = $this->getHeaders($authorization, "application/json", $idempotencyKey, null);
+        $requestOptions = [
+            "verify" => false,
+            "body" => $body,
+            "headers" => $headers
+        ];
+        
+        return $this->handleRequest($method, $path, $authorization, $requestOptions);
     }
 
     /**
@@ -210,10 +263,11 @@ private function getRequestUrl($path)
      * @param SdkAuthorization $authorization
      * @param string|null $contentType
      * @param string|null $idempotencyKey
+     * @param string|null $telemetryData
      * @return array
      * @throws CheckoutAuthorizationException
      */
-    private function getHeaders(SdkAuthorization $authorization, $contentType, $idempotencyKey)
+    private function getHeaders(SdkAuthorization $authorization, $contentType, $idempotencyKey, $telemetryData)
     {
         $headers = [
             "User-agent" => CheckoutUtils::PROJECT_NAME . "/" . CheckoutUtils::PROJECT_VERSION,
@@ -226,6 +280,9 @@ private function getHeaders(SdkAuthorization $authorization, $contentType, $idem
         if (!empty($idempotencyKey)) {
             $headers["Cko-Idempotency-Key"] = $idempotencyKey;
         }
+        if (!empty($telemetryData)) {
+            $headers["Cko-Sdk-Telemetry"] = base64_encode(json_encode($telemetryData));
+        }
         return $headers;
     }
 
diff --git a/lib/Checkout/CheckoutConfiguration.php b/lib/Checkout/CheckoutConfiguration.php
index 20cc0e3..b44f5e6 100644
--- a/lib/Checkout/CheckoutConfiguration.php
+++ b/lib/Checkout/CheckoutConfiguration.php
@@ -15,24 +15,29 @@ final class CheckoutConfiguration
     private $httpClientBuilder;
 
     private $logger;
+    
+    private $enableTelemetry;
 
     /**
      * @param SdkCredentialsInterface $sdkCredentials
      * @param Environment $environment
      * @param HttpClientBuilderInterface $httpClientBuilder
      * @param LoggerInterface $logger
+     * @param bool $enableTelemetry
      */
     public function __construct(
         SdkCredentialsInterface    $sdkCredentials,
         Environment                $environment,
         HttpClientBuilderInterface $httpClientBuilder,
-        LoggerInterface            $logger
+        LoggerInterface            $logger,
+        $enableTelemetry = true
     ) {
         $this->sdkCredentials = $sdkCredentials;
         $this->environment = $environment;
         $this->httpClientBuilder = $httpClientBuilder;
         $this->logger = $logger;
         $this->environmentSubdomain = null;
+        $this ->enableTelemetry = $enableTelemetry;
     }
 
     /**
@@ -79,4 +84,12 @@ public function getLogger()
     {
         return $this->logger;
     }
+
+    /**
+     * @return bool
+     */
+    public function isEnableTelemetry()
+    {
+        return $this->enableTelemetry;
+    }
 }
diff --git a/lib/Checkout/CheckoutOAuthSdkBuilder.php b/lib/Checkout/CheckoutOAuthSdkBuilder.php
index a180816..4bc0191 100644
--- a/lib/Checkout/CheckoutOAuthSdkBuilder.php
+++ b/lib/Checkout/CheckoutOAuthSdkBuilder.php
@@ -84,8 +84,10 @@ public function build()
             $this->getSdkCredentials(),
             $this->environment,
             $this->httpClientBuilder,
-            $this->logger
+            $this->logger,
+            $this->enableTelemetry
         );
+        // $configuration = $this->getCheckoutConfiguration();
         if ($this->environmentSubdomain !== null) {
             $configuration->setEnvironmentSubdomain($this->environmentSubdomain);
         }
diff --git a/lib/Checkout/CheckoutStaticKeysSdkBuilder.php b/lib/Checkout/CheckoutStaticKeysSdkBuilder.php
index ec8b6aa..d0dc639 100644
--- a/lib/Checkout/CheckoutStaticKeysSdkBuilder.php
+++ b/lib/Checkout/CheckoutStaticKeysSdkBuilder.php
@@ -48,8 +48,10 @@ public function build()
             $this->getSdkCredentials(),
             $this->environment,
             $this->httpClientBuilder,
-            $this->logger
+            $this->logger,
+            $this->enableTelemetry
         );
+        // $configuration = $this->getCheckoutConfiguration();
         if ($this->environmentSubdomain !== null) {
             $configuration->setEnvironmentSubdomain($this->environmentSubdomain);
         }
diff --git a/lib/Checkout/Common/RequestMetrics.php b/lib/Checkout/Common/RequestMetrics.php
new file mode 100644
index 0000000..8d95ccf
--- /dev/null
+++ b/lib/Checkout/Common/RequestMetrics.php
@@ -0,0 +1,17 @@
+<?php
+
+namespace Checkout\Common;
+
+class RequestMetrics
+{
+    public $prevRequestId;
+    public $requestId;
+    public $prevRequestDuration;
+
+    public function __construct($prevRequestId = null, $requestId = null, $prevRequestDuration = null)
+    {
+        $this->prevRequestId = $prevRequestId;
+        $this->requestId = $requestId;
+        $this->prevRequestDuration = $prevRequestDuration;
+    }
+}
diff --git a/lib/Checkout/Common/TelemetryQueue.php b/lib/Checkout/Common/TelemetryQueue.php
new file mode 100644
index 0000000..a20f6a2
--- /dev/null
+++ b/lib/Checkout/Common/TelemetryQueue.php
@@ -0,0 +1,48 @@
+<?php
+
+namespace Checkout\Common;
+
+class TelemetryQueue
+{
+    const MAX_COUNT_IN_TELEMETRY_QUEUE = 10;
+    private $queue;
+    private $mutex;
+
+    public function __construct()
+    {
+        $this->queue = [];
+        $this->mutex = fopen(sys_get_temp_dir() . '/telemetry_queue.lock', 'w+');
+    }
+
+    public function __destruct()
+    {
+        if ($this->mutex) {
+            fclose($this->mutex);
+        }
+    }
+
+    public function enqueue($metrics)
+    {
+        flock($this->mutex, LOCK_EX);
+        try {
+            if (count($this->queue) < self::MAX_COUNT_IN_TELEMETRY_QUEUE) {
+                $this->queue[] = $metrics;
+            }
+        } finally {
+            flock($this->mutex, LOCK_UN);
+        }
+    }
+
+    public function dequeue()
+    {
+        flock($this->mutex, LOCK_EX);
+        try {
+            if (empty($this->queue)) {
+                return null;
+            }
+            return array_shift($this->queue);
+        } finally {
+            flock($this->mutex, LOCK_UN);
+        }
+    }
+}
diff --git a/lib/Checkout/OAuthSdkCredentials.php b/lib/Checkout/OAuthSdkCredentials.php
index 85e2147..9b18872 100644
--- a/lib/Checkout/OAuthSdkCredentials.php
+++ b/lib/Checkout/OAuthSdkCredentials.php
@@ -85,10 +85,14 @@ public function getAuthorization($authorizationType)
      */
     private function getAccessToken()
     {
+        printf("ClientId: %s\n", $this->clientId);
+        printf("ClientSecret: %s\n", $this->clientSecret);
+    
         if (!is_null($this->accessToken) && $this->accessToken->isValid()) {
             return $this->accessToken;
         }
         try {
+            printf("Scope string: %s\n", implode(" ", $this->scopes));
             $response = $this->client->request("POST", $this->authorizationUri, [
                 "verify" => false,
                 "headers" => [
@@ -101,7 +105,10 @@ private function getAccessToken()
                     "scope" => implode(" ", $this->scopes)
                 ]
             ]);
+            printf($response);
             $body = json_decode($response->getBody(), true);
+            printf("This is a body!");
+            print_r($body);
             $expirationDate = new DateTime();
             $expirationDate->add(new DateInterval("PT" . $body["expires_in"] . "S"));
             $this->accessToken = new OAuthAccessToken($body["access_token"], $expirationDate);
diff --git a/lib/Checkout/Previous/CheckoutStaticKeysPreviousSdkBuilder.php b/lib/Checkout/Previous/CheckoutStaticKeysPreviousSdkBuilder.php
index 1dcf2bf..8725ecc 100644
--- a/lib/Checkout/Previous/CheckoutStaticKeysPreviousSdkBuilder.php
+++ b/lib/Checkout/Previous/CheckoutStaticKeysPreviousSdkBuilder.php
@@ -54,7 +54,8 @@ public function build()
             $this->getSdkCredentials(),
             $this->environment,
             $this->httpClientBuilder,
-            $this->logger
+            $this->logger,
+            $this->enableTelemetry
         );
         if ($this->environmentSubdomain !== null) {
             $configuration->setEnvironmentSubdomain($this->environmentSubdomain);
diff --git a/test/Checkout/Tests/TelemetryTest.php b/test/Checkout/Tests/TelemetryTest.php
new file mode 100644
index 0000000..7a67851
--- /dev/null
+++ b/test/Checkout/Tests/TelemetryTest.php
@@ -0,0 +1,158 @@
+<?php
+
+namespace Checkout\Tests;
+
+use Checkout\CheckoutSdk;
+use Checkout\Environment;
+use GuzzleHttp\Client;
+use GuzzleHttp\Handler\MockHandler;
+use GuzzleHttp\HandlerStack;
+use GuzzleHttp\Middleware;
+use GuzzleHttp\Psr7\Response;
+use PHPUnit\Framework\TestCase;
+use Checkout\HttpClientBuilderInterface;
+
+class TelemetryTest extends UnitTestFixture
+{
+    private $container = [];
+    private $mockHandler;
+    
+    protected function setUp(): void
+    {
+        parent::setUp();
+        
+        $this->container = [];
+        
+        $this->mockHandler = new MockHandler();
+        
+        $handlerStack = HandlerStack::create($this->mockHandler);
+        
+        $history = Middleware::history($this->container);
+        $handlerStack->push($history);
+    }
+    
+    /**
+     * Counts requests that contain a specific header
+     */
+    private function countRequestsWithHeader($header)
+    {
+        $count = 0;
+        foreach ($this->container as $transaction) {
+            if ($transaction['request']->hasHeader($header)) {
+                $count++;
+            }
+        }
+        return $count;
+    }
+    
+    /**
+     * Creates a CheckoutApi instance with the specified telemetry setting
+     */
+    private function createCheckoutApi($enableTelemetry)
+    {
+        $handlerStack = HandlerStack::create($this->mockHandler);
+        $history = Middleware::history($this->container);
+        $handlerStack->push($history);
+
+        $client = new Client(['handler' => $handlerStack]);
+
+        // Set up the mock builder to return this client
+        $httpBuilder = $this->createMock(HttpClientBuilderInterface::class);
+        $httpBuilder->expects($this->once())
+            ->method("getClient")
+            ->willReturn($client);
+        $builder = CheckoutSdk::builder()
+            ->previous()
+            ->staticKeys()
+            ->publicKey(parent::$validPreviousPk)
+            ->secretKey(parent::$validPreviousSk)
+            ->httpClientBuilder($httpBuilder)
+            ->environment(Environment::sandbox());
+            
+        if (!$enableTelemetry) {
+            $builder = $builder->enableTelemetry(false);
+        } else {
+            $builder = $builder->enableTelemetry(true);
+        }
+        
+        // Add mock responses to the handler for the number of requests we expect
+        for ($i = 0; $i < 3; $i++) {
+            $this->mockHandler->append(new Response(200, [], '{"data": []}'));
+        }
+        
+        return $builder->build();
+    }
+    
+    /**
+     * @test
+     */
+    public function shouldSendTelemetryByDefault()
+    {
+        $checkoutApi = $this->createCheckoutApi(true);
+        
+        for ($i = 0; $i < 3; $i++) {
+            $checkoutApi->getEventsClient()->retrieveAllEventTypes();
+        }
+        
+        // Telemetry headers should be present in all requests except the first
+        $expectedTelemetryHeaderCount = 2;
+        $telemetryHeaderCount = $this->countRequestsWithHeader('cko-sdk-telemetry');
+        
+        $this->assertEquals(
+            $expectedTelemetryHeaderCount,
+            $telemetryHeaderCount,
+            "Expected exactly {$expectedTelemetryHeaderCount} requests to contain the telemetry header"
+        );
+    }
+    
+    /**
+     * @test
+     */
+    public function shouldNotSendTelemetryWhenOptedOut()
+    {
+        $checkoutApi = $this->createCheckoutApi(false);
+        
+        for ($i = 0; $i < 3; $i++) {
+            $checkoutApi->getEventsClient()->retrieveAllEventTypes();
+        }
+        
+        // No requests should contain telemetry headers
+        $telemetryHeaderCount = $this->countRequestsWithHeader('cko-sdk-telemetry');
+        
+        $this->assertEquals(
+            0,
+            $telemetryHeaderCount,
+            'Expected no requests to contain the telemetry header'
+        );
+    }
+    
+    /**
+     * @test
+     */
+    public function shouldHandleTelemetryQueueAndBottleneck()
+    {
+        $checkoutApi = $this->createCheckoutApi(true);
+        
+        // Add more mock responses for the additional requests
+        for ($i = 0; $i < 7; $i++) {  // 7 more to make total of 10
+            $this->mockHandler->append(new Response(200, [], '{"data": []}'));
+        }
+        
+        $numRequests = 10;
+        
+        for ($i = 0; $i < $numRequests; $i++) {
+            $checkoutApi->getEventsClient()->retrieveAllEventTypes();
+        }
+        
+        // Since telemetry starts being sent from the second request,
+        // we expect (numRequests - 1) telemetry headers
+        $expectedTelemetryHeaderCount = $numRequests - 1;
+        $telemetryHeaderCount = $this->countRequestsWithHeader('cko-sdk-telemetry');
+        
+        $this->assertEquals(
+            $expectedTelemetryHeaderCount,
+            $telemetryHeaderCount,
+            "Expected {$expectedTelemetryHeaderCount} requests to contain the telemetry header"
+        );
+    }
+}