diff --git a/.evergreen/config/generated/build/build-extension.yml b/.evergreen/config/generated/build/build-extension.yml
index 1ccde5f97..a74e18776 100644
--- a/.evergreen/config/generated/build/build-extension.yml
+++ b/.evergreen/config/generated/build/build-extension.yml
@@ -7,6 +7,9 @@ tasks:
         vars:
           PHP_VERSION: "8.4"
       - func: "compile extension"
+        # TODO: remove once 1.21.0 is released
+        vars:
+          EXTENSION_BRANCH: "v1.x"
       - func: "upload extension"
   - name: "build-php-8.4-lowest"
     tags: ["build", "php8.4", "lowest", "pr", "tag"]
@@ -16,7 +19,9 @@ tasks:
           PHP_VERSION: "8.4"
       - func: "compile extension"
         vars:
-          EXTENSION_VERSION: "1.20.0"
+          # TODO: change to "EXTENSION_VERSION: 1.21.0" once 1.21.0 is released
+          # EXTENSION_VERSION: "1.21.0"
+          EXTENSION_BRANCH: "v1.x"
       - func: "upload extension"
   - name: "build-php-8.4-next-stable"
     tags: ["build", "php8.4", "next-stable", "pr", "tag"]
@@ -26,7 +31,9 @@ tasks:
           PHP_VERSION: "8.4"
       - func: "compile extension"
         vars:
-          EXTENSION_BRANCH: "v1.20"
+          # TODO: change to "v1.21" once 1.21.0 is released
+          # EXTENSION_BRANCH: "v1.21"
+          EXTENSION_BRANCH: "v1.x"
       - func: "upload extension"
   - name: "build-php-8.4-next-minor"
     tags: ["build", "php8.4", "next-minor"]
@@ -45,6 +52,9 @@ tasks:
         vars:
           PHP_VERSION: "8.3"
       - func: "compile extension"
+        # TODO: remove once 1.21.0 is released
+        vars:
+          EXTENSION_BRANCH: "v1.x"
       - func: "upload extension"
   - name: "build-php-8.3-lowest"
     tags: ["build", "php8.3", "lowest", "pr", "tag"]
@@ -54,7 +64,9 @@ tasks:
           PHP_VERSION: "8.3"
       - func: "compile extension"
         vars:
-          EXTENSION_VERSION: "1.20.0"
+          # TODO: change to "EXTENSION_VERSION: 1.21.0" once 1.21.0 is released
+          # EXTENSION_VERSION: "1.21.0"
+          EXTENSION_BRANCH: "v1.x"
       - func: "upload extension"
   - name: "build-php-8.3-next-stable"
     tags: ["build", "php8.3", "next-stable", "pr", "tag"]
@@ -64,7 +76,9 @@ tasks:
           PHP_VERSION: "8.3"
       - func: "compile extension"
         vars:
-          EXTENSION_BRANCH: "v1.20"
+          # TODO: change to "v1.21" once 1.21.0 is released
+          # EXTENSION_BRANCH: "v1.21"
+          EXTENSION_BRANCH: "v1.x"
       - func: "upload extension"
   - name: "build-php-8.3-next-minor"
     tags: ["build", "php8.3", "next-minor"]
@@ -83,6 +97,9 @@ tasks:
         vars:
           PHP_VERSION: "8.2"
       - func: "compile extension"
+        # TODO: remove once 1.21.0 is released
+        vars:
+          EXTENSION_BRANCH: "v1.x"
       - func: "upload extension"
   - name: "build-php-8.2-lowest"
     tags: ["build", "php8.2", "lowest", "pr", "tag"]
@@ -92,7 +109,9 @@ tasks:
           PHP_VERSION: "8.2"
       - func: "compile extension"
         vars:
-          EXTENSION_VERSION: "1.20.0"
+          # TODO: change to "EXTENSION_VERSION: 1.21.0" once 1.21.0 is released
+          # EXTENSION_VERSION: "1.21.0"
+          EXTENSION_BRANCH: "v1.x"
       - func: "upload extension"
   - name: "build-php-8.2-next-stable"
     tags: ["build", "php8.2", "next-stable", "pr", "tag"]
@@ -102,7 +121,9 @@ tasks:
           PHP_VERSION: "8.2"
       - func: "compile extension"
         vars:
-          EXTENSION_BRANCH: "v1.20"
+          # TODO: change to "v1.21" once 1.21.0 is released
+          # EXTENSION_BRANCH: "v1.21"
+          EXTENSION_BRANCH: "v1.x"
       - func: "upload extension"
   - name: "build-php-8.2-next-minor"
     tags: ["build", "php8.2", "next-minor"]
@@ -121,6 +142,9 @@ tasks:
         vars:
           PHP_VERSION: "8.1"
       - func: "compile extension"
+        # TODO: remove once 1.21.0 is released
+        vars:
+          EXTENSION_BRANCH: "v1.x"
       - func: "upload extension"
   - name: "build-php-8.1-lowest"
     tags: ["build", "php8.1", "lowest", "pr", "tag"]
@@ -130,7 +154,9 @@ tasks:
           PHP_VERSION: "8.1"
       - func: "compile extension"
         vars:
-          EXTENSION_VERSION: "1.20.0"
+          # TODO: change to "EXTENSION_VERSION: 1.21.0" once 1.21.0 is released
+          # EXTENSION_VERSION: "1.21.0"
+          EXTENSION_BRANCH: "v1.x"
       - func: "upload extension"
   - name: "build-php-8.1-next-stable"
     tags: ["build", "php8.1", "next-stable", "pr", "tag"]
@@ -140,7 +166,9 @@ tasks:
           PHP_VERSION: "8.1"
       - func: "compile extension"
         vars:
-          EXTENSION_BRANCH: "v1.20"
+          # TODO: change to "v1.21" once 1.21.0 is released
+          # EXTENSION_BRANCH: "v1.21"
+          EXTENSION_BRANCH: "v1.x"
       - func: "upload extension"
   - name: "build-php-8.1-next-minor"
     tags: ["build", "php8.1", "next-minor"]
diff --git a/.evergreen/config/templates/build/build-extension.yml b/.evergreen/config/templates/build/build-extension.yml
index 869c0a9e4..98da2976d 100644
--- a/.evergreen/config/templates/build/build-extension.yml
+++ b/.evergreen/config/templates/build/build-extension.yml
@@ -5,6 +5,9 @@
         vars:
           PHP_VERSION: "%phpVersion%"
       - func: "compile extension"
+        # TODO: remove once 1.21.0 is released
+        vars:
+          EXTENSION_BRANCH: "v1.x"
       - func: "upload extension"
   - name: "build-php-%phpVersion%-lowest"
     tags: ["build", "php%phpVersion%", "lowest", "pr", "tag"]
@@ -14,7 +17,9 @@
           PHP_VERSION: "%phpVersion%"
       - func: "compile extension"
         vars:
-          EXTENSION_VERSION: "1.20.0"
+          # TODO: change to "EXTENSION_VERSION: 1.21.0" once 1.21.0 is released
+          # EXTENSION_VERSION: "1.21.0"
+          EXTENSION_BRANCH: "v1.x"
       - func: "upload extension"
   - name: "build-php-%phpVersion%-next-stable"
     tags: ["build", "php%phpVersion%", "next-stable", "pr", "tag"]
@@ -24,7 +29,9 @@
           PHP_VERSION: "%phpVersion%"
       - func: "compile extension"
         vars:
-          EXTENSION_BRANCH: "v1.20"
+          # TODO: change to "v1.21" once 1.21.0 is released
+          # EXTENSION_BRANCH: "v1.21"
+          EXTENSION_BRANCH: "v1.x"
       - func: "upload extension"
   - name: "build-php-%phpVersion%-next-minor"
     tags: ["build", "php%phpVersion%", "next-minor"]
diff --git a/.github/workflows/coding-standards.yml b/.github/workflows/coding-standards.yml
index 462e4d67e..10bcc251d 100644
--- a/.github/workflows/coding-standards.yml
+++ b/.github/workflows/coding-standards.yml
@@ -13,7 +13,9 @@ on:
 
 env:
   PHP_VERSION: "8.2"
-  DRIVER_VERSION: "stable"
+  # TODO: change to "stable" once 1.21.0 is released
+  # DRIVER_VERSION: "stable"
+  DRIVER_VERSION: "mongodb/mongo-php-driver@v1.x"
 
 jobs:
   phpcs:
diff --git a/.github/workflows/generator.yml b/.github/workflows/generator.yml
index 2427a41eb..fd755509c 100644
--- a/.github/workflows/generator.yml
+++ b/.github/workflows/generator.yml
@@ -13,9 +13,9 @@ on:
 
 env:
   PHP_VERSION: "8.2"
-  # TODO: change to "stable" once 1.20.0 is released
+  # TODO: change to "stable" once 1.21.0 is released
   # DRIVER_VERSION: "stable"
-  DRIVER_VERSION: "mongodb/mongo-php-driver@v1.20"
+  DRIVER_VERSION: "mongodb/mongo-php-driver@v1.x"
 
 jobs:
   psalm:
diff --git a/.github/workflows/static-analysis.yml b/.github/workflows/static-analysis.yml
index 0103bdcd1..5a7d6fbf3 100644
--- a/.github/workflows/static-analysis.yml
+++ b/.github/workflows/static-analysis.yml
@@ -19,7 +19,9 @@ on:
 
 env:
   PHP_VERSION: "8.2"
-  DRIVER_VERSION: "stable"
+  # TODO: change to "stable" once 1.21.0 is released
+  # DRIVER_VERSION: "stable"
+  DRIVER_VERSION: "mongodb/mongo-php-driver@v1.x"
 
 jobs:
   psalm:
diff --git a/.github/workflows/tests.yml b/.github/workflows/tests.yml
index 36640a724..194414fb4 100644
--- a/.github/workflows/tests.yml
+++ b/.github/workflows/tests.yml
@@ -12,7 +12,9 @@ on:
       - "feature/*"
 
 env:
-  DRIVER_VERSION: "stable"
+  # TODO: change to "stable" once 1.21.0 is released
+  # DRIVER_VERSION: "stable"
+  DRIVER_VERSION: "mongodb/mongo-php-driver@v1.x"
 
 jobs:
   phpunit:
diff --git a/composer.json b/composer.json
index 3b5738ae1..118943bb3 100644
--- a/composer.json
+++ b/composer.json
@@ -13,7 +13,7 @@
         "php": "^8.1",
         "ext-hash": "*",
         "ext-json": "*",
-        "ext-mongodb": "^1.20.0",
+        "ext-mongodb": "^1.21.0",
         "composer-runtime-api": "^2.0",
         "psr/log": "^1.1.4|^2|^3",
         "symfony/polyfill-php80": "^1.27",
diff --git a/src/Operation/BulkWrite.php b/src/Operation/BulkWrite.php
index 5c0b67ea5..c8f695675 100644
--- a/src/Operation/BulkWrite.php
+++ b/src/Operation/BulkWrite.php
@@ -91,6 +91,14 @@ class BulkWrite implements Executable
      *  * upsert (boolean): When true, a new document is created if no document
      *    matches the query. The default is false.
      *
+     * Supported options for replaceOne and updateOne operations:
+     *
+     *  * sort (document): Determines which document the operation modifies if
+     *    the query selects multiple documents.
+     *
+     *    This is not supported for server versions < 8.0 and will result in an
+     *    exception at execution time if used.
+     *
      * Supported options for updateMany and updateOne operations:
      *
      *  * arrayFilters (document array): A set of filters specifying to which
@@ -372,6 +380,10 @@ private function validateOperations(array $operations, ?DocumentCodec $codec, En
                         throw InvalidArgumentException::expectedDocumentType(sprintf('$operations[%d]["%s"][2]["collation"]', $i, $type), $args[2]['collation']);
                     }
 
+                    if (isset($args[2]['sort']) && ! is_document($args[2]['sort'])) {
+                        throw InvalidArgumentException::expectedDocumentType(sprintf('$operations[%d]["%s"][2]["sort"]', $i, $type), $args[2]['sort']);
+                    }
+
                     if (! is_bool($args[2]['upsert'])) {
                         throw InvalidArgumentException::invalidType(sprintf('$operations[%d]["%s"][2]["upsert"]', $i, $type), $args[2]['upsert'], 'boolean');
                     }
@@ -413,6 +425,14 @@ private function validateOperations(array $operations, ?DocumentCodec $codec, En
                         throw InvalidArgumentException::expectedDocumentType(sprintf('$operations[%d]["%s"][2]["collation"]', $i, $type), $args[2]['collation']);
                     }
 
+                    if (isset($args[2]['sort']) && ! is_document($args[2]['sort'])) {
+                        throw InvalidArgumentException::expectedDocumentType(sprintf('$operations[%d]["%s"][2]["sort"]', $i, $type), $args[2]['sort']);
+                    }
+
+                    if (isset($args[2]['sort']) && $args[2]['multi']) {
+                        throw new InvalidArgumentException(sprintf('"sort" option cannot be used with $operations[%d]["%s"]', $i, $type));
+                    }
+
                     if (! is_bool($args[2]['upsert'])) {
                         throw InvalidArgumentException::invalidType(sprintf('$operations[%d]["%s"][2]["upsert"]', $i, $type), $args[2]['upsert'], 'boolean');
                     }
diff --git a/src/Operation/ReplaceOne.php b/src/Operation/ReplaceOne.php
index 3cec99ff0..843640923 100644
--- a/src/Operation/ReplaceOne.php
+++ b/src/Operation/ReplaceOne.php
@@ -74,6 +74,12 @@ class ReplaceOne implements Executable
      *    Parameters can then be accessed as variables in an aggregate
      *    expression context (e.g. "$$var").
      *
+     *   * sort (document): Determines which document the operation modifies if
+     *     the query selects multiple documents.
+     *
+     *     This is not supported for server versions < 8.0 and will result in an
+     *     exception at execution time if used.
+     *
      *  * writeConcern (MongoDB\Driver\WriteConcern): Write concern.
      *
      * @param string       $databaseName   Database name
diff --git a/src/Operation/Update.php b/src/Operation/Update.php
index 5d011da28..2016d89a8 100644
--- a/src/Operation/Update.php
+++ b/src/Operation/Update.php
@@ -149,6 +149,14 @@ public function __construct(private string $databaseName, private string $collec
             throw InvalidArgumentException::expectedDocumentType('"let" option', $options['let']);
         }
 
+        if (isset($options['sort']) && ! is_document($options['sort'])) {
+            throw InvalidArgumentException::expectedDocumentType('"sort" option', $options['sort']);
+        }
+
+        if (isset($options['sort']) && $options['multi']) {
+            throw new InvalidArgumentException('"sort" option cannot be used with multi-document updates');
+        }
+
         if (isset($options['bypassDocumentValidation']) && ! $options['bypassDocumentValidation']) {
             unset($options['bypassDocumentValidation']);
         }
@@ -270,8 +278,10 @@ private function createUpdateOptions(): array
             }
         }
 
-        if (isset($this->options['collation'])) {
-            $updateOptions['collation'] = (object) $this->options['collation'];
+        foreach (['collation', 'sort'] as $option) {
+            if (isset($this->options[$option])) {
+                $updateOptions[$option] = (object) $this->options[$option];
+            }
         }
 
         return $updateOptions;
diff --git a/src/Operation/UpdateOne.php b/src/Operation/UpdateOne.php
index 17bc4a554..d7bbe57cb 100644
--- a/src/Operation/UpdateOne.php
+++ b/src/Operation/UpdateOne.php
@@ -72,6 +72,12 @@ class UpdateOne implements Executable, Explainable
      *    Parameters can then be accessed as variables in an aggregate
      *    expression context (e.g. "$$var").
      *
+     *  * sort (document): Determines which document the operation modifies if
+     *    the query selects multiple documents.
+     *
+     *    This is not supported for server versions < 8.0 and will result in an
+     *    exception at execution time if used.
+     *
      *  * writeConcern (MongoDB\Driver\WriteConcern): Write concern.
      *
      * @param string       $databaseName   Database name
diff --git a/tests/Operation/BulkWriteTest.php b/tests/Operation/BulkWriteTest.php
index d64fc351f..30d5c6374 100644
--- a/tests/Operation/BulkWriteTest.php
+++ b/tests/Operation/BulkWriteTest.php
@@ -217,6 +217,16 @@ public function testReplaceOneCollationOptionTypeCheck($collation): void
         ]);
     }
 
+    #[DataProvider('provideInvalidDocumentValues')]
+    public function testReplaceOneSortOptionTypeCheck($sort): void
+    {
+        $this->expectException(InvalidArgumentException::class);
+        $this->expectExceptionMessageMatches('/Expected \$operations\[0\]\["replaceOne"\]\[2\]\["sort"\] to have type "document" \(array or object\) but found ".+"/');
+        new BulkWrite($this->getDatabaseName(), $this->getCollectionName(), [
+            [BulkWrite::REPLACE_ONE => [['x' => 1], ['y' => 1], ['sort' => $sort]]],
+        ]);
+    }
+
     #[DataProvider('provideInvalidBooleanValues')]
     public function testReplaceOneUpsertOptionTypeCheck($upsert): void
     {
@@ -322,6 +332,15 @@ public function testUpdateManyCollationOptionTypeCheck($collation): void
         ]);
     }
 
+    public function testUpdateManyProhibitsSortOption(): void
+    {
+        $this->expectException(InvalidArgumentException::class);
+        $this->expectExceptionMessage('"sort" option cannot be used with $operations[0]["updateMany"]');
+        new BulkWrite($this->getDatabaseName(), $this->getCollectionName(), [
+            [BulkWrite::UPDATE_MANY => [['x' => 1], ['$set' => ['y' => 1]], ['sort' => ['z' => 1]]]],
+        ]);
+    }
+
     #[DataProvider('provideInvalidBooleanValues')]
     public function testUpdateManyUpsertOptionTypeCheck($upsert): void
     {
@@ -410,6 +429,16 @@ public function testUpdateOneCollationOptionTypeCheck($collation): void
         ]);
     }
 
+    #[DataProvider('provideInvalidDocumentValues')]
+    public function testUpdateOneSortOptionTypeCheck($sort): void
+    {
+        $this->expectException(InvalidArgumentException::class);
+        $this->expectExceptionMessageMatches('/Expected \$operations\[0\]\["updateOne"\]\[2\]\["sort"\] to have type "document" \(array or object\) but found ".+"/');
+        new BulkWrite($this->getDatabaseName(), $this->getCollectionName(), [
+            [BulkWrite::UPDATE_ONE => [['x' => 1], ['$set' => ['y' => 1]], ['sort' => $sort]]],
+        ]);
+    }
+
     #[DataProvider('provideInvalidBooleanValues')]
     public function testUpdateOneUpsertOptionTypeCheck($upsert): void
     {
diff --git a/tests/Operation/UpdateTest.php b/tests/Operation/UpdateTest.php
index 6c6f590d5..9617c77e8 100644
--- a/tests/Operation/UpdateTest.php
+++ b/tests/Operation/UpdateTest.php
@@ -40,6 +40,7 @@ public static function provideInvalidConstructorOptions()
             'collation' => self::getInvalidDocumentValues(),
             'hint' => self::getInvalidHintValues(),
             'multi' => self::getInvalidBooleanValues(),
+            'sort' => self::getInvalidDocumentValues(),
             'session' => self::getInvalidSessionValues(),
             'upsert' => self::getInvalidBooleanValues(),
             'writeConcern' => self::getInvalidWriteConcernValues(),
@@ -55,6 +56,13 @@ public function testConstructorMultiOptionProhibitsReplacementDocumentOrEmptyPip
         new Update($this->getDatabaseName(), $this->getCollectionName(), ['x' => 1], $update, ['multi' => true]);
     }
 
+    public function testConstructorMultiOptionProhibitsSortOption(): void
+    {
+        $this->expectException(InvalidArgumentException::class);
+        $this->expectExceptionMessage('"sort" option cannot be used with multi-document updates');
+        new Update($this->getDatabaseName(), $this->getCollectionName(), ['x' => 1], ['$set' => ['x' => 2]], ['multi' => true, 'sort' => ['x' => 1]]);
+    }
+
     public function testExplainableCommandDocument(): void
     {
         $options = [
diff --git a/tests/UnifiedSpecTests/UnifiedSpecTest.php b/tests/UnifiedSpecTests/UnifiedSpecTest.php
index 5dad387fb..b41a67f38 100644
--- a/tests/UnifiedSpecTests/UnifiedSpecTest.php
+++ b/tests/UnifiedSpecTests/UnifiedSpecTest.php
@@ -37,11 +37,6 @@ class UnifiedSpecTest extends FunctionalTestCase
         // mongoc_cluster_stream_for_server does not retry handshakes (CDRIVER-4532, PHPLIB-1033, PHPLIB-1042)
         'retryable-reads/retryable reads handshake failures' => 'Handshakes are not retried (CDRIVER-4532)',
         'retryable-writes/retryable writes handshake failures' => 'Handshakes are not retried (CDRIVER-4532)',
-        // sort option for update operations is not supported (PHPLIB-1492)
-        'crud/BulkWrite replaceOne-sort' => 'Sort for replace operations is not supported (PHPLIB-1492)',
-        'crud/BulkWrite updateOne-sort' => 'Sort for update operations is not supported (PHPLIB-1492)',
-        'crud/replaceOne-sort' => 'Sort for replace operations is not supported (PHPLIB-1492)',
-        'crud/updateOne-sort' => 'Sort for update operations is not supported (PHPLIB-1492)',
         'crud/bypassDocumentValidation' => 'bypassDocumentValidation is handled by libmongoc (PHPLIB-1576)',
     ];
 
diff --git a/tests/UnifiedSpecTests/Util.php b/tests/UnifiedSpecTests/Util.php
index 8adb2923a..d508d7d65 100644
--- a/tests/UnifiedSpecTests/Util.php
+++ b/tests/UnifiedSpecTests/Util.php
@@ -105,10 +105,10 @@ final class Util
             'findOne' => ['let', 'filter', 'session', 'allowDiskUse', 'allowPartialResults', 'batchSize', 'collation', 'comment', 'cursorType', 'hint', 'max', 'maxAwaitTimeMS', 'maxScan', 'maxTimeMS', 'min', 'modifiers', 'noCursorTimeout', 'oplogReplay', 'projection', 'returnKey', 'showRecordId', 'skip', 'snapshot', 'sort'],
             'findOneAndReplace' => ['let', 'returnDocument', 'filter', 'replacement', 'session', 'projection', 'returnDocument', 'upsert', 'arrayFilters', 'bypassDocumentValidation', 'collation', 'hint', 'maxTimeMS', 'new', 'remove', 'sort', 'comment'],
             'rename' => ['to', 'comment', 'dropTarget'],
-            'replaceOne' => ['let', 'filter', 'replacement', 'session', 'upsert', 'arrayFilters', 'bypassDocumentValidation', 'collation', 'hint', 'comment'],
+            'replaceOne' => ['let', 'filter', 'replacement', 'session', 'upsert', 'arrayFilters', 'bypassDocumentValidation', 'collation', 'hint', 'comment', 'sort'],
             'findOneAndUpdate' => ['let', 'returnDocument', 'filter', 'update', 'session', 'upsert', 'projection', 'remove', 'arrayFilters', 'bypassDocumentValidation', 'collation', 'hint', 'maxTimeMS', 'sort', 'comment'],
             'updateMany' => ['let', 'filter', 'update', 'session', 'upsert', 'arrayFilters', 'bypassDocumentValidation', 'collation', 'hint', 'comment'],
-            'updateOne' => ['let', 'filter', 'update', 'session', 'upsert', 'arrayFilters', 'bypassDocumentValidation', 'collation', 'hint', 'comment'],
+            'updateOne' => ['let', 'filter', 'update', 'session', 'upsert', 'arrayFilters', 'bypassDocumentValidation', 'collation', 'hint', 'comment', 'sort'],
             'updateSearchIndex' => ['name', 'definition'],
             'insertMany' => ['documents', 'session', 'ordered', 'bypassDocumentValidation', 'comment'],
             'insertOne' => ['document', 'session', 'bypassDocumentValidation', 'comment'],