diff --git a/CHANGELOG b/CHANGELOG
index 5abb052..db28f43 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -1,3 +1,9 @@
+Version 0.9.1 (2025-04-11)
+--------------------------
+Add Emitter Server Anonymization support (#152)
+Fix Psalm issues in Tracker (close #137) thanks to @XWB
+Update PHP version in CD
+
 Version 0.9.0 (2025-03-03)
 --------------------------
 Bump Ubuntu Version in GH Actions
diff --git a/src/Constants.php b/src/Constants.php
index 8bb2e48..5741ce4 100644
--- a/src/Constants.php
+++ b/src/Constants.php
@@ -45,7 +45,7 @@ class Constants {
      * - SSL: the default for whether or not to use SSL Encryption
      * - Type: the default for what type of request the emitter will be making (POST or GET)
      */
-    const TRACKER_VERSION       = "php-0.9.0";
+    const TRACKER_VERSION       = "php-0.9.1";
     const DEFAULT_BASE_64       = true;
     const DEBUG_LOG_FILES       = true;
     const CONTEXT_SCHEMA        = "iglu:com.snowplowanalytics.snowplow/contexts/jsonschema/1-0-1";
@@ -61,6 +61,7 @@ class Constants {
     const DEFAULT_SSL           = false;
     const DEFAULT_REQ_TYPE      = "POST";
     const NO_RETRY_STATUS_CODES = array(400, 401, 403, 410, 422);
+    const SERVER_ANONYMIZATION  = "SP-Anonymous";
 
     /**
      * Settings for the Synchronous Emitter
diff --git a/src/Emitters/CurlEmitter.php b/src/Emitters/CurlEmitter.php
index aced2fe..347a3d2 100644
--- a/src/Emitters/CurlEmitter.php
+++ b/src/Emitters/CurlEmitter.php
@@ -31,6 +31,7 @@ class CurlEmitter extends Emitter {
     private $debug;
     private $requests_results;
     private $debug_payloads;
+    private $server_anoymization;
 
     // Curl Specific Parameters
 
@@ -49,14 +50,17 @@ class CurlEmitter extends Emitter {
      * @param int|null $buffer_size - Emitter buffer size
      * @param bool $debug - Debug mode
      * @param int|null $curl_timeout - Maximum time the request is allowed to take, in seconds
+     * @param bool|null $server_anonymization - Whether to enable Server Anonymization and not collect the IP or Network User ID. Defaults to false.
      */
-    public function __construct($uri, $protocol = NULL, $type = NULL, $buffer_size = NULL, $debug = false, $curl_timeout = NULL) {
+    public function __construct($uri, $protocol = NULL, $type = NULL, $buffer_size = NULL, $debug = false, $curl_timeout = NULL, $server_anonymization = false) {
         $this->type           = $this->getRequestType($type);
         $this->url            = $this->getCollectorUrl($this->type, $uri, $protocol);
         $this->curl_limit     = $this->type == "POST" ? self::CURL_AMOUNT_POST : self::CURL_AMOUNT_GET;
         $this->rolling_window = $this->type == "POST" ? self::CURL_WINDOW_POST : self::CURL_WINDOW_GET;
         $this->curl_timeout   = $curl_timeout;
 
+        $this->server_anonymization = $server_anonymization;
+
         // If debug is on create a requests_results array
         if ($debug === true) {
             $this->debug = true;
@@ -222,19 +226,22 @@ private function rollingCurl($curls, $debug) {
      */
     private function getCurlRequest($payload, $type) {
         $ch = curl_init($this->url);
+        $header = array();
         if ($type == "POST") {
-            $header = array(
-                'Content-Type: '.self::POST_CONTENT_TYPE,
-                'Accept: '.self::POST_ACCEPT,
-                'Content-Length: '.strlen($payload));
+            $header[] = 'Content-Type: '.self::POST_CONTENT_TYPE;
+            $header[] = 'Accept: '.self::POST_ACCEPT;
+            $header[] = 'Content-Length: '.strlen($payload);
             curl_setopt($ch, CURLOPT_CUSTOMREQUEST, "POST");
             curl_setopt($ch, CURLOPT_POSTFIELDS, $payload);
-            curl_setopt($ch, CURLOPT_HTTPHEADER, $header);
         }
         else {
             curl_setopt($ch, CURLOPT_CUSTOMREQUEST, "GET");
             curl_setopt($ch, CURLOPT_URL, $this->url."?".$payload);
         }
+
+        if ($this->server_anonymization) $header[] = self::SERVER_ANONYMIZATION.": *";
+
+        if ($header) curl_setopt($ch, CURLOPT_HTTPHEADER, $header);
         curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
         if ($this->curl_timeout != NULL) {
             curl_setopt($ch, CURLOPT_TIMEOUT, $this->curl_timeout);
diff --git a/src/Emitters/SocketEmitter.php b/src/Emitters/SocketEmitter.php
index 8753835..774abe6 100644
--- a/src/Emitters/SocketEmitter.php
+++ b/src/Emitters/SocketEmitter.php
@@ -36,6 +36,7 @@ class SocketEmitter extends Emitter {
     private $requests_results;
     private $max_retry_attempts;
     private $retry_backoff_ms;
+    private $server_anonymization;
 
     // Socket Parameters
 
@@ -53,14 +54,16 @@ class SocketEmitter extends Emitter {
      * @param bool|null $debug - If debug is on
      * @param int|null $max_retry_attempts - The maximum number of times to retry a request. Defaults to 1.
      * @param int|null $retry_backoff_ms - The number of milliseconds to backoff before retrying a request. Defaults to 100ms.
+     * @param bool|null $server_anonymization - Whether to enable Server Anonymization and not collect the IP or Network User ID. Defaults to false.
      */
-    public function __construct($uri, $ssl = NULL, $type = NULL, $timeout = NULL, $buffer_size = NULL, $debug = NULL, $max_retry_attempts = NULL, $retry_backoff_ms = NULL) {
+    public function __construct($uri, $ssl = NULL, $type = NULL, $timeout = NULL, $buffer_size = NULL, $debug = NULL, $max_retry_attempts = NULL, $retry_backoff_ms = NULL, $server_anonymization = false) {
         $this->type    = $this->getRequestType($type);
         $this->uri     = $uri;
         $this->ssl     = $ssl == NULL ? self::DEFAULT_SSL : (bool) $ssl;
         $this->timeout = $timeout == NULL ? self::SOCKET_TIMEOUT : $timeout;
         $this->max_retry_attempts = $max_retry_attempts;
         $this->retry_backoff_ms = $retry_backoff_ms;
+        $this->server_anonymization = $server_anonymization;
 
         // If debug is on create a requests_results array
         if ($debug === true) {
@@ -240,6 +243,7 @@ private function getRequestBody($uri, $data, $type) {
             $req.= "Host: ".$uri."\r\n";
             $req.= "Content-Type: ".self::POST_CONTENT_TYPE."\r\n";
             $req.= "Content-length: ".strlen($data)."\r\n";
+            if ($this->server_anonymization) $req.= self::SERVER_ANONYMIZATION.": *\r\n";
             $req.= "Accept: ".self::POST_ACCEPT."\r\n\r\n";
             $req.= $data."\r\n\r\n";
         }
@@ -247,6 +251,7 @@ private function getRequestBody($uri, $data, $type) {
             $req = "GET http://".$uri.self::GET_PATH."?".$data." ";
             $req.= "HTTP/1.1\r\n";
             $req.= "Host: ".$uri."\r\n";
+            if ($this->server_anonymization) $req.= self::SERVER_ANONYMIZATION.": *\r\n";
             $req.= "Query: ".$data."\r\n";
             $req.= "\r\n";
         }
diff --git a/src/Emitters/SyncEmitter.php b/src/Emitters/SyncEmitter.php
index a2b7ae7..2ac0660 100644
--- a/src/Emitters/SyncEmitter.php
+++ b/src/Emitters/SyncEmitter.php
@@ -35,6 +35,7 @@ class SyncEmitter extends Emitter {
     private $requests_results;
     private $max_retry_attempts;
     private $retry_backoff_ms;
+    private $server_anonymization;
 
     /**
      * Creates a Synchronous Emitter
@@ -46,12 +47,14 @@ class SyncEmitter extends Emitter {
      * @param bool|null $debug - If debug is on
      * @param int|null $max_retry_attempts - The maximum number of times to retry a request. Defaults to 1.
      * @param int|null $retry_backoff_ms - The number of milliseconds to backoff before retrying a request. Defaults to 100ms.
+     * @param bool|null $server_anonymization - Whether to enable Server Anonymization and not collect the IP or Network User ID. Defaults to false.
      */
-    public function __construct($uri, $protocol = NULL, $type = NULL, $buffer_size = NULL, $debug = false, $max_retry_attempts = NULL, $retry_backoff_ms = NULL) {
+    public function __construct($uri, $protocol = NULL, $type = NULL, $buffer_size = NULL, $debug = false, $max_retry_attempts = NULL, $retry_backoff_ms = NULL, $server_anonymization = false) {
         $this->type = $this->getRequestType($type);
         $this->url  = $this->getCollectorUrl($this->type, $uri, $protocol);
         $this->max_retry_attempts = $max_retry_attempts;
         $this->retry_backoff_ms = $retry_backoff_ms;
+        $this->server_anonymization = $server_anonymization;
 
         // If debug is on create a requests_results array
         if ($debug === true) {
@@ -115,20 +118,23 @@ private function curlRequest($data, $type, $retry_request_manager = NULL) {
 
         // Create a cURL handle, set transfer options and execute
         $ch = curl_init($this->url);
+        $header = array();
         if ($type == 'POST') {
             $json_data = json_encode($data);
-            $header = array(
-                'Content-Type: '.self::POST_CONTENT_TYPE,
-                'Accept: '.self::POST_ACCEPT,
-                'Content-Length: '.strlen($json_data));
+            $header[] = 'Content-Type: '.self::POST_CONTENT_TYPE;
+            $header[] = 'Accept: '.self::POST_ACCEPT;
+            $header[] = 'Content-Length: '.strlen($json_data);
             curl_setopt($ch, CURLOPT_CUSTOMREQUEST, "POST");
             curl_setopt($ch, CURLOPT_POSTFIELDS, $json_data);
-            curl_setopt($ch, CURLOPT_HTTPHEADER, $header);
         }
         else {
             curl_setopt($ch, CURLOPT_CUSTOMREQUEST, "GET");
             curl_setopt($ch, CURLOPT_URL, $this->url."?".http_build_query($data));
         }
+
+        if ($this->server_anonymization) $header[] = self::SERVER_ANONYMIZATION.': *';
+        if ($header) curl_setopt($ch, CURLOPT_HTTPHEADER, $header);
+
         curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
         curl_exec($ch);
 
diff --git a/src/Tracker.php b/src/Tracker.php
index d9ffa25..f61ab93 100644
--- a/src/Tracker.php
+++ b/src/Tracker.php
@@ -23,6 +23,7 @@
 namespace Snowplow\Tracker;
 
 use Ramsey\Uuid\Uuid;
+use Snowplow\Tracker\Emitter;
 
 class Tracker extends Constants {
 
@@ -36,7 +37,7 @@ class Tracker extends Constants {
     /**
      * Constructs a new tracker object with emitter(s) and a subject.
      *
-     * @param emitter|array $emitter - Emitter object, used for sending event payloads to for processing
+     * @param Emitter|array $emitter - Emitter object, used for sending event payloads to for processing
      * @param subject $subject - Subject object, contains extra information which is parcelled with the event
      * @param string|null $namespace
      * @param string|null $app_id