diff --git a/vendor/magento/module-quote/Model/Quote/Item/Repository.php b/vendor/magento/module-quote/Model/Quote/Item/Repository.php
index 6fb512a619de..4f7864db29a8 100644
--- a/vendor/magento/module-quote/Model/Quote/Item/Repository.php
+++ b/vendor/magento/module-quote/Model/Quote/Item/Repository.php
@@ -7,28 +7,31 @@
 namespace Magento\Quote\Model\Quote\Item;
 
 use Magento\Catalog\Api\ProductRepositoryInterface;
+use Magento\Framework\App\ObjectManager;
 use Magento\Framework\Exception\CouldNotSaveException;
 use Magento\Framework\Exception\InputException;
 use Magento\Framework\Exception\NoSuchEntityException;
 use Magento\Quote\Api\CartItemRepositoryInterface;
 use Magento\Quote\Api\CartRepositoryInterface;
+use Magento\Quote\Api\Data\CartInterface;
+use Magento\Quote\Api\Data\CartItemInterface;
 use Magento\Quote\Api\Data\CartItemInterfaceFactory;
+use Magento\Quote\Model\QuoteMutexInterface;
+use Magento\Quote\Model\QuoteRepository;
 
 /**
  * Repository for quote item.
+ *
+ * @SuppressWarnings(PHPMD.CouplingBetweenObjects)
  */
 class Repository implements CartItemRepositoryInterface
 {
     /**
-     * Quote repository.
-     *
      * @var CartRepositoryInterface
      */
     protected $quoteRepository;
 
     /**
-     * Product repository.
-     *
      * @var ProductRepositoryInterface
      */
     protected $productRepository;
@@ -48,25 +51,33 @@ class Repository implements CartItemRepositoryInterface
      */
     private $cartItemOptionsProcessor;
 
+    /**
+     * @var ?QuoteMutexInterface
+     */
+    private ?QuoteMutexInterface $quoteMutex;
+
     /**
      * @param CartRepositoryInterface $quoteRepository
      * @param ProductRepositoryInterface $productRepository
      * @param CartItemInterfaceFactory $itemDataFactory
      * @param CartItemOptionsProcessor $cartItemOptionsProcessor
      * @param CartItemProcessorInterface[] $cartItemProcessors
+     * @param QuoteMutexInterface|null $quoteMutex
      */
     public function __construct(
         CartRepositoryInterface $quoteRepository,
         ProductRepositoryInterface $productRepository,
         CartItemInterfaceFactory $itemDataFactory,
         CartItemOptionsProcessor $cartItemOptionsProcessor,
-        array $cartItemProcessors = []
+        array $cartItemProcessors = [],
+        ?QuoteMutexInterface $quoteMutex = null
     ) {
         $this->quoteRepository = $quoteRepository;
         $this->productRepository = $productRepository;
         $this->itemDataFactory = $itemDataFactory;
         $this->cartItemOptionsProcessor = $cartItemOptionsProcessor;
         $this->cartItemProcessors = $cartItemProcessors;
+        $this->quoteMutex = $quoteMutex ?: ObjectManager::getInstance()->get(QuoteMutexInterface::class);
     }
 
     /**
@@ -89,7 +100,7 @@ public function getList($cartId)
     /**
      * @inheritdoc
      */
-    public function save(\Magento\Quote\Api\Data\CartItemInterface $cartItem)
+    public function save(CartItemInterface $cartItem)
     {
         /** @var \Magento\Quote\Model\Quote $quote */
         $cartId = $cartItem->getQuoteId();
@@ -99,12 +110,35 @@ public function save(\Magento\Quote\Api\Data\CartItemInterface $cartItem)
             );
         }
 
-        $quote = $this->quoteRepository->getActive($cartId);
+        return $this->quoteMutex->execute(
+            [$cartId],
+            \Closure::fromCallable([$this, 'saveItem']),
+            [$cartItem]
+        );
+    }
+
+    /**
+     * Save cart item.
+     *
+     * @param CartItemInterface $cartItem
+     * @return CartItemInterface
+     * @throws NoSuchEntityException
+     * @SuppressWarnings(PHPMD.UnusedPrivateMethod)
+     */
+    private function saveItem(CartItemInterface $cartItem)
+    {
+        $cartId = (int)$cartItem->getQuoteId();
+        if ($this->quoteRepository instanceof QuoteRepository) {
+            $quote = $this->getNonCachedActiveQuote($cartId);
+        } else {
+            $quote = $this->quoteRepository->getActive($cartId);
+        }
         $quoteItems = $quote->getItems();
         $quoteItems[] = $cartItem;
         $quote->setItems($quoteItems);
         $this->quoteRepository->save($quote);
         $quote->collectTotals();
+
         return $quote->getLastAddedItem();
     }
 
@@ -130,4 +164,28 @@ public function deleteById($cartId, $itemId)
 
         return true;
     }
+
+    /**
+     * Returns quote repository without internal cache.
+     *
+     * Prevents usage of cached quote that causes incorrect quote items update by concurrent web-api requests.
+     *
+     * @param int $cartId
+     * @return CartInterface
+     * @throws NoSuchEntityException
+     */
+    private function getNonCachedActiveQuote(int $cartId): CartInterface
+    {
+        $cachedQuote = $this->quoteRepository->getActive($cartId);
+        $className = get_class($this->quoteRepository);
+        $quote = ObjectManager::getInstance()->create($className)->getActive($cartId);
+        foreach ($quote->getItems() as $quoteItem) {
+            $cachedQuoteItem = $cachedQuote->getItemById($quoteItem->getId());
+            if ($cachedQuoteItem) {
+                $quoteItem->setExtensionAttributes($cachedQuoteItem->getExtensionAttributes());
+            }
+        }
+
+        return $quote;
+    }
 }
diff --git a/vendor/magento/module-quote/Model/QuoteIdMutex.php b/vendor/magento/module-quote/Model/QuoteIdMutex.php
new file mode 100644
index 000000000000..aa5bcb089dc5
--- /dev/null
+++ b/vendor/magento/module-quote/Model/QuoteIdMutex.php
@@ -0,0 +1,68 @@
+<?php
+/************************************************************************
+ *
+ * Copyright 2024 Adobe
+ * All Rights Reserved.
+ *
+ * NOTICE: All information contained herein is, and remains
+ * the property of Adobe and its suppliers, if any. The intellectual
+ * and technical concepts contained herein are proprietary to Adobe
+ * and its suppliers and are protected by all applicable intellectual
+ * property laws, including trade secret and copyright laws.
+ * Dissemination of this information or reproduction of this material
+ * is strictly forbidden unless prior written permission is obtained
+ * from Adobe.
+ * ***********************************************************************
+ */
+declare(strict_types=1);
+
+namespace Magento\Quote\Model;
+
+use Magento\Framework\App\ResourceConnection;
+
+/**
+ * @inheritDoc
+ */
+class QuoteIdMutex implements QuoteMutexInterface
+{
+    /**
+     * @var ResourceConnection
+     */
+    private $resourceConnection;
+
+    /**
+     * @param ResourceConnection $resourceConnection
+     */
+    public function __construct(
+        ResourceConnection $resourceConnection
+    ) {
+        $this->resourceConnection = $resourceConnection;
+    }
+
+    /**
+     * @inheritDoc
+     */
+    public function execute(array $maskedIds, callable $callable, array $args = [])
+    {
+        if (empty($maskedIds)) {
+            throw new \InvalidArgumentException('Quote ids must be provided');
+        }
+
+        $connection = $this->resourceConnection->getConnection();
+        $connection->beginTransaction();
+        $query = $connection->select()
+            ->from($this->resourceConnection->getTableName('quote'), 'entity_id')
+            ->where('entity_id IN (?)', $maskedIds)
+            ->forUpdate(true);
+        $connection->query($query);
+
+        try {
+            $result = $callable(...$args);
+            $this->resourceConnection->getConnection()->commit();
+            return $result;
+        } catch (\Throwable $e) {
+            $this->resourceConnection->getConnection()->rollBack();
+            throw $e;
+        }
+    }
+}
diff --git a/vendor/magento/module-quote/etc/di.xml b/vendor/magento/module-quote/etc/di.xml
index 01821c63801a..e7267eaa9821 100644
--- a/vendor/magento/module-quote/etc/di.xml
+++ b/vendor/magento/module-quote/etc/di.xml
@@ -143,4 +143,9 @@
             <argument name="generalMessage" xsi:type="string" translatable="true">Enter a valid payment method and try again.</argument>
         </arguments>
     </type>
+    <type name="Magento\Quote\Model\Quote\Item\Repository">
+        <arguments>
+            <argument name="quoteMutex" xsi:type="object">Magento\Quote\Model\QuoteIdMutex</argument>
+        </arguments>
+    </type>
 </config>