diff --git a/src/Client.php b/src/Client.php
index f4e7cfa..25436df 100644
--- a/src/Client.php
+++ b/src/Client.php
@@ -42,6 +42,11 @@ class Client
      */
     private bool $isConnected = false;
 
+    /**
+     * Whether the next operation must establish a fresh physical connection.
+     */
+    private bool $reconnect = false;
+
     /**
      * Socket / receive idle timeout in seconds.
      *
@@ -86,6 +91,8 @@ class Client
     public const TRANSACTION_TIMEOUT_ERROR = 50;
     public const TRANSACTION_ABORTED_ERROR = 251;
 
+    private const PRIMARY_CHANGE_ERRORS = [189, 10107, 11602, 13435, 13436];
+
     // Transaction states
     public const TRANSACTION_NONE = 'none';
     public const TRANSACTION_STARTING = 'starting';
@@ -1689,8 +1696,10 @@ public function close(): void
     /**
      * Physically close a failed socket without writing session cleanup to it.
      */
-    private function invalidate(): void
+    private function invalidate(bool $preserveSessions = false): void
     {
+        $sessions = $preserveSessions ? $this->sessions : [];
+
         try {
             if ($this->client instanceof CoroutineClient) {
                 @$this->client->close();
@@ -1701,6 +1710,10 @@ private function invalidate(): void
             // The transport may already be closed or only partially initialized.
         } finally {
             $this->reset();
+            if ($preserveSessions) {
+                $this->sessions = $sessions;
+                $this->reconnect = true;
+            }
         }
     }
 
@@ -1710,6 +1723,7 @@ private function invalidate(): void
     private function reset(): void
     {
         $this->isConnected = false;
+        $this->reconnect = false;
         $this->sessions = [];
         $this->clusterTime = null;
         $this->operationTime = null;
@@ -1800,7 +1814,12 @@ private function parseResponse(string $response, int $responseLength): stdClass|
             $writeError = $result->writeErrors[0] ?? null;
 
             if (\is_object($writeError) && isset($writeError->errmsg, $writeError->code)) {
-                throw new Exception($writeError->errmsg, $writeError->code);
+                $code = (int)$writeError->code;
+                if (self::isPrimaryChange($code)) {
+                    $this->invalidate(preserveSessions: true);
+                }
+
+                throw new Exception($writeError->errmsg, $code);
             }
 
             $this->invalidate();
@@ -1811,6 +1830,10 @@ private function parseResponse(string $response, int $responseLength): stdClass|
             $code = (int)($result->code ?? 0);
             $name = (string)($result->codeName ?? 'MongoError');
 
+            if (self::isPrimaryChange($code)) {
+                $this->invalidate(preserveSessions: true);
+            }
+
             throw new Exception('E' . $code . ' ' . $name . ': ' . $result->errmsg, $code);
         }
 
@@ -1831,6 +1854,11 @@ private function parseResponse(string $response, int $responseLength): stdClass|
         throw new Exception('Invalid unsuccessful response');
     }
 
+    private static function isPrimaryChange(int $code): bool
+    {
+        return \in_array($code, self::PRIMARY_CHANGE_ERRORS, true);
+    }
+
     /**
      * Check if an exception represents a transient transaction error.
      *
@@ -2039,6 +2067,20 @@ public function getSessionState(array $session): array
      */
     private function validateConnection(): void
     {
+        if ($this->reconnect) {
+            $sessions = $this->sessions;
+            $this->reconnect = false;
+
+            try {
+                $this->connect();
+            } finally {
+                $this->sessions = $sessions;
+                if (!$this->isConnected || !$this->client->isConnected()) {
+                    $this->reconnect = true;
+                }
+            }
+        }
+
         if (!$this->isConnected) {
             throw new Exception('Client is not connected to MongoDB');
         }
diff --git a/tests/ClientTest.php b/tests/ClientTest.php
index 4cab1b3..d43e8ff 100644
--- a/tests/ClientTest.php
+++ b/tests/ClientTest.php
@@ -490,6 +490,141 @@ public function testDecodedMongoCommandErrorDoesNotCloseTransport(): void
         $this->assertTrue($transport->open);
     }
 
+    public function testPrimaryChangeErrorsCloseTransportAndPreserveSessions(): void
+    {
+        foreach ([189, 10107, 11602, 13435, 13436] as $code) {
+            $transport = new SyncTransportDouble();
+            $transport->receives = [[
+                'result' => $this->frame([
+                    'ok' => 0.0,
+                    'errmsg' => 'primary changed',
+                    'code' => $code,
+                    'codeName' => 'PrimaryChanged',
+                ]),
+                'error' => 0,
+            ]];
+            $client = $this->client($transport);
+            $this->seedState($client);
+            $sessions = $this->get($client, 'sessions');
+
+            $exception = $this->receiveException($client);
+
+            try {
+                $this->assertSame($code, $exception->getCode());
+                $this->assertSame([[true]], $transport->closes);
+                $this->assertSame($sessions, $this->get($client, 'sessions'));
+                $this->assertFalse($this->get($client, 'isConnected'));
+                $this->assertTrue($this->get($client, 'reconnect'));
+                $this->assertConnectionContextCleared($client);
+            } finally {
+                $this->set($client, 'sessions', []);
+            }
+        }
+    }
+
+    public function testPrimaryChangeWriteErrorClosesTransportAndPreservesSessions(): void
+    {
+        $transport = new SyncTransportDouble();
+        $transport->receives = [[
+            'result' => $this->frame([
+                'ok' => 1.0,
+                'writeErrors' => [[
+                    'errmsg' => 'not primary',
+                    'code' => 10107,
+                ]],
+            ]),
+            'error' => 0,
+        ]];
+        $client = $this->client($transport);
+        $this->seedState($client);
+        $sessions = $this->get($client, 'sessions');
+
+        $exception = $this->receiveException($client);
+
+        try {
+            $this->assertSame(10107, $exception->getCode());
+            $this->assertSame([[true]], $transport->closes);
+            $this->assertSame($sessions, $this->get($client, 'sessions'));
+            $this->assertFalse($this->get($client, 'isConnected'));
+            $this->assertTrue($this->get($client, 'reconnect'));
+            $this->assertConnectionContextCleared($client);
+        } finally {
+            $this->set($client, 'sessions', []);
+        }
+    }
+
+    public function testPermanentWriteErrorDoesNotCloseTransport(): void
+    {
+        $transport = new SyncTransportDouble();
+        $transport->receives = [[
+            'result' => $this->frame([
+                'ok' => 1.0,
+                'writeErrors' => [[
+                    'errmsg' => 'duplicate key',
+                    'code' => 11000,
+                ]],
+            ]),
+            'error' => 0,
+        ]];
+        $client = $this->client($transport);
+
+        $exception = $this->receiveException($client);
+
+        $this->assertSame(11000, $exception->getCode());
+        $this->assertSame([], $transport->closes);
+        $this->assertTrue($transport->open);
+    }
+
+    public function testTransactionRetriesOnAFreshTransportAfterPrimaryChange(): void
+    {
+        $transport = new SyncTransportDouble();
+        $transport->receives = [
+            [
+                'result' => $this->frame([
+                    'ok' => 0.0,
+                    'errmsg' => 'not primary',
+                    'code' => 10107,
+                    'codeName' => 'NotWritablePrimary',
+                ]),
+                'error' => 0,
+            ],
+            ['result' => $this->frame(['ok' => 1.0]), 'error' => 0],
+            ['result' => $this->frame(['ok' => 1.0]), 'error' => 0],
+            ['result' => $this->frame(['ok' => 1.0]), 'error' => 0],
+        ];
+        $client = $this->reconnectingClient($transport);
+        $identifier = (object) ['id' => new Binary(str_repeat("\1", 16), Binary::TYPE_GENERIC)];
+        $session = ['id' => $identifier, 'sessionId' => 'session'];
+        $this->set($client, 'isConnected', true);
+        $this->set($client, 'sessions', [
+            'session' => [
+                'id' => $identifier,
+                'state' => Client::TRANSACTION_NONE,
+                'txnNumber' => 0,
+                'lastUse' => time(),
+                'operationTime' => null,
+                'clusterTime' => null,
+                'options' => [],
+                'retryableWriteNumber' => 0,
+            ],
+        ]);
+
+        $result = $client->withTransaction(
+            $session,
+            fn (array $transaction): mixed => $client->query(['ping' => 1, 'session' => $transaction]),
+            ['retryDelayMs' => 0],
+        );
+        $sessions = $this->get($client, 'sessions');
+
+        $this->assertSame(1.0, $result->ok);
+        $this->assertSame(Client::TRANSACTION_COMMITTED, $sessions['session']['state']);
+        $this->assertSame(2, $sessions['session']['txnNumber']);
+        $this->assertSame([[true]], $transport->closes);
+        $this->assertCount(1, $transport->connects);
+        $this->assertFalse($this->get($client, 'reconnect'));
+        $this->set($client, 'sessions', []);
+    }
+
     private function assertStateCleared(Client $client): void
     {
         $this->assertFalse($this->get($client, 'isConnected'));
@@ -562,7 +697,18 @@ private function reconnectingClient(SwooleClient|CoroutineClient $transport): Re
     private function seedState(Client $client): void
     {
         $this->seedConnectionContext($client);
-        $this->set($client, 'sessions', ['session' => ['id' => 'session']]);
+        $this->set($client, 'sessions', [
+            'session' => [
+                'id' => (object) ['id' => 'session'],
+                'state' => Client::TRANSACTION_NONE,
+                'txnNumber' => 0,
+                'lastUse' => time(),
+                'operationTime' => null,
+                'clusterTime' => null,
+                'options' => [],
+                'retryableWriteNumber' => 0,
+            ],
+        ]);
     }
 
     private function seedConnectionContext(Client $client): void