diff --git a/.evergreen/config.yml b/.evergreen/config.yml
index 1c2d6a43a..877faf0ef 100644
--- a/.evergreen/config.yml
+++ b/.evergreen/config.yml
@@ -199,6 +199,38 @@ functions:
         script: |
           DRIVERS_TOOLS="${DRIVERS_TOOLS}" sh ${DRIVERS_TOOLS}/.evergreen/atlas_data_lake/run-mongohouse-local.sh
 
+  "create serverless instance":
+    - command: shell.exec
+      params:
+        working_dir: "src"
+        shell: bash
+        script: |-
+          ${PREPARE_SHELL}
+          export PROJECT=${PROJECT}
+          export SERVERLESS_DRIVERS_GROUP=${SERVERLESS_DRIVERS_GROUP}
+          export SERVERLESS_API_PUBLIC_KEY=${SERVERLESS_API_PUBLIC_KEY}
+          export SERVERLESS_API_PRIVATE_KEY=${SERVERLESS_API_PRIVATE_KEY}
+          export SERVERLESS_ATLAS_USER=${SERVERLESS_ATLAS_USER}
+          export SERVERLESS_ATLAS_PASSWORD=${SERVERLESS_ATLAS_PASSWORD}
+          sh ${PROJECT_DIRECTORY}/.evergreen/serverless/create-instance.sh
+    - command: expansions.update
+      params:
+        file: src/serverless-expansion.yml
+
+  "delete serverless instance":
+    - command: shell.exec
+      params:
+        shell: bash
+        script: |-
+          set -o errexit
+          export SERVERLESS_DRIVERS_GROUP=${SERVERLESS_DRIVERS_GROUP}
+          export SERVERLESS_API_PUBLIC_KEY=${SERVERLESS_API_PUBLIC_KEY}
+          export SERVERLESS_API_PRIVATE_KEY=${SERVERLESS_API_PRIVATE_KEY}
+          export SERVERLESS_ATLAS_USER=${SERVERLESS_ATLAS_USER}
+          export SERVERLESS_ATLAS_PASSWORD=${SERVERLESS_ATLAS_PASSWORD}
+          export SERVERLESS_INSTANCE_NAME=${SERVERLESS_INSTANCE_NAME}
+          sh ${PROJECT_DIRECTORY}/.evergreen/serverless/delete-instance.sh
+
   "run tests":
     - command: shell.exec
       type: test
@@ -226,6 +258,20 @@ functions:
            export PATH="${PHP_PATH}/bin:$PATH"
            PHP_VERSION=${PHP_VERSION} TESTS="atlas-data-lake" AUTH=${AUTH} SSL=${SSL} MONGODB_URI="${MONGODB_URI}" sh ${PROJECT_DIRECTORY}/.evergreen/run-tests.sh
 
+  "run serverless tests":
+    - command: shell.exec
+      type: test
+      params:
+        working_dir: "src"
+        shell: bash
+        script: |-
+          ${PREPARE_SHELL}
+          export MONGODB_IS_SERVERLESS=on
+          export MONGODB_USERNAME=${SERVERLESS_ATLAS_USER}
+          export MONGODB_PASSWORD=${SERVERLESS_ATLAS_PASSWORD}
+          export PATH="${PHP_PATH}/bin:$PATH"
+          PHP_VERSION=${PHP_VERSION} TESTS="serverless" MONGODB_URI="${MONGODB_URI}" sh ${PROJECT_DIRECTORY}/.evergreen/run-tests.sh
+
   "cleanup":
     - command: shell.exec
       params:
@@ -377,6 +423,15 @@ tasks:
         - func: "run tests"
           vars:
             TESTS: "versioned-api"
+
+    - name: "test-serverless"
+      tags: ["serverless"]
+      commands:
+        - func: "create serverless instance"
+          vars:
+            PROJECT: "mongo-php-library"
+        - func: "run serverless tests"
+        - func: "delete serverless instance"
 # }}}
 
 
@@ -631,3 +686,10 @@ buildvariants:
   run_on: rhel70
   tasks:
     - .versioned-api
+
+- matrix_name: "serverless"
+  matrix_spec: { "php-edge-versions": "latest-stable", "driver-versions": "latest-dev" }
+  display_name: "Serverless"
+  run_on: rhel70
+  tasks:
+    - .serverless
diff --git a/.evergreen/run-tests.sh b/.evergreen/run-tests.sh
index eb78a6893..5cf1978cd 100755
--- a/.evergreen/run-tests.sh
+++ b/.evergreen/run-tests.sh
@@ -63,6 +63,10 @@ case "$TESTS" in
       php vendor/bin/simple-phpunit --configuration phpunit.evergreen.xml --group versioned-api $PHPUNIT_OPTS
       ;;
 
+   serverless)
+      php vendor/bin/simple-phpunit --configuration phpunit.evergreen.xml --group serverless $PHPUNIT_OPTS
+      ;;
+
    *)
       php vendor/bin/simple-phpunit --configuration phpunit.evergreen.xml $PHPUNIT_OPTS
       ;;
diff --git a/.evergreen/serverless/create-instance.sh b/.evergreen/serverless/create-instance.sh
new file mode 100755
index 000000000..0a56c8e33
--- /dev/null
+++ b/.evergreen/serverless/create-instance.sh
@@ -0,0 +1,87 @@
+#!/bin/bash
+
+set -o errexit
+set +o xtrace # disable xtrace to ensure credentials aren't leaked
+
+if [ -z "$PROJECT" ]; then
+    echo "Project name must be provided via PROJECT environment variable"
+    exit 1
+fi
+INSTANCE_NAME="$RANDOM-$PROJECT"
+
+if [ -z "$SERVERLESS_DRIVERS_GROUP" ]; then
+    echo "Drivers Atlas group must be provided via SERVERLESS_DRIVERS_GROUP environment variable"
+    exit 1
+fi
+
+if [ -z "$SERVERLESS_API_PRIVATE_KEY" ]; then
+    echo "Atlas API private key must be provided via SERVERLESS_API_PRIVATE_KEY environment variable"
+    exit 1
+fi
+
+if [ -z "$SERVERLESS_API_PUBLIC_KEY" ]; then
+    echo "Atlas API public key must be provided via SERVERLESS_API_PUBLIC_KEY environment variable"
+    exit 1
+fi
+
+echo "creating new serverless instance \"${INSTANCE_NAME}\"..."
+
+DIR=$(dirname $0)
+API_BASE_URL="https://account-dev.mongodb.com/api/atlas/v1.0/groups/$SERVERLESS_DRIVERS_GROUP"
+
+curl \
+  -u "$SERVERLESS_API_PUBLIC_KEY:$SERVERLESS_API_PRIVATE_KEY" \
+  --silent \
+  --show-error \
+  -X POST \
+  --digest \
+  --header "Accept: application/json" \
+  --header "Content-Type: application/json" \
+  "$API_BASE_URL/serverless?pretty=true" \
+  --data "
+    {
+      \"name\" : \"${INSTANCE_NAME}\",
+      \"providerSettings\" : {
+        \"providerName\": \"SERVERLESS\",
+        \"backingProviderName\": \"GCP\",
+        \"instanceSizeName\" : \"SERVERLESS_V2\",
+        \"regionName\" : \"CENTRAL_US\"
+      }
+    }"
+
+echo ""
+
+if [ "Windows_NT" = "$OS" ]; then
+  PYTHON_BINARY=C:/python/Python38/python.exe
+else
+  PYTHON_BINARY=python
+fi
+
+SECONDS=0
+while [ true ]; do
+    API_RESPONSE=`SERVERLESS_INSTANCE_NAME=$INSTANCE_NAME bash $DIR/get-instance.sh`
+    STATE_NAME=`echo $API_RESPONSE | $PYTHON_BINARY -c "import sys, json; print(json.load(sys.stdin)['stateName'])" | tr -d '\r\n'`
+
+    if [ "$STATE_NAME" = "IDLE" ]; then
+        duration="$SECONDS"
+        echo "setup done! ($(($duration / 60))m $(($duration % 60))s elapsed)"
+        echo "SERVERLESS_INSTANCE_NAME=\"$INSTANCE_NAME\""
+        SRV_ADDRESS=$(echo $API_RESPONSE | $PYTHON_BINARY -c "import sys, json; print(json.load(sys.stdin)['connectionStrings']['standardSrv'])" | tr -d '\r\n')
+        echo "MONGODB_SRV_URI=\"$SRV_ADDRESS\""
+        STANDARD_ADDRESS=$(echo $API_RESPONSE | $PYTHON_BINARY -c "import sys, json; print(json.load(sys.stdin)['connectionStrings']['standard'].replace('&authSource=admin', ''))" | tr -d '\r\n')
+        echo "MONGODB_URI=\"$STANDARD_ADDRESS\""
+        cat <<EOF > serverless-expansion.yml
+MONGODB_URI: "$STANDARD_ADDRESS"
+MONGODB_SRV_URI: "$SRV_ADDRESS"
+SERVERLESS_INSTANCE_NAME: "$INSTANCE_NAME"
+SSL: ssl
+AUTH: auth
+TOPOLOGY: sharded_cluster
+SERVERLESS: serverless
+EOF
+        exit 0
+    else
+        echo "setup still in progress, status=$STATE_NAME, sleeping for 1 minute..."
+        sleep 60
+    fi
+done
diff --git a/.evergreen/serverless/delete-instance.sh b/.evergreen/serverless/delete-instance.sh
new file mode 100755
index 000000000..ba412d4d4
--- /dev/null
+++ b/.evergreen/serverless/delete-instance.sh
@@ -0,0 +1,40 @@
+#!/bin/bash
+
+set -o errexit
+set +o xtrace
+
+if [ -z "$SERVERLESS_INSTANCE_NAME" ]; then
+    echo "Instance name must be provided via SERVERLESS_INSTANCE_NAME environment variable"
+    exit 1
+fi
+
+if [ -z "$SERVERLESS_DRIVERS_GROUP" ]; then
+    echo "Drivers Atlas group must be provided via SERVERLESS_DRIVERS_GROUP environment variable"
+    exit 1
+fi
+
+if [ -z "$SERVERLESS_API_PRIVATE_KEY" ]; then
+    echo "Atlas API private key must be provided via SERVERLESS_API_PRIVATE_KEY environment variable"
+    exit 1
+fi
+
+if [ -z "$SERVERLESS_API_PUBLIC_KEY" ]; then
+    echo "Atlas API public key must be provided via SERVERLESS_API_PUBLIC_KEY environment variable"
+    exit 1
+fi
+
+echo "deleting serverless instance \"${SERVERLESS_INSTANCE_NAME}\"..."
+
+API_BASE_URL="https://account-dev.mongodb.com/api/atlas/v1.0/groups/$SERVERLESS_DRIVERS_GROUP"
+
+curl \
+  --silent \
+  --show-error \
+  -u "$SERVERLESS_API_PUBLIC_KEY:$SERVERLESS_API_PRIVATE_KEY" \
+  -X DELETE \
+  --digest \
+  --header "Accept: application/json" \
+  --header "Content-Type: application/json" \
+  "${API_BASE_URL}/serverless/${SERVERLESS_INSTANCE_NAME}?pretty=true"
+
+echo ""
diff --git a/.evergreen/serverless/get-instance.sh b/.evergreen/serverless/get-instance.sh
new file mode 100755
index 000000000..496400dc7
--- /dev/null
+++ b/.evergreen/serverless/get-instance.sh
@@ -0,0 +1,37 @@
+#!/bin/bash
+
+set -o errexit
+set +o xtrace
+
+if [ -z "$SERVERLESS_INSTANCE_NAME" ]; then
+    echo "Instance name must be provided via SERVERLESS_INSTANCE_NAME environment variable"
+    exit 1
+fi
+
+if [ -z "$SERVERLESS_DRIVERS_GROUP" ]; then
+    echo "Drivers Atlas group must be provided via SERVERLESS_DRIVERS_GROUP environment variable"
+    exit 1
+fi
+
+if [ -z "$SERVERLESS_API_PRIVATE_KEY" ]; then
+    echo "Atlas API private key must be provided via SERVERLESS_API_PRIVATE_KEY environment variable"
+    exit 1
+fi
+
+if [ -z "$SERVERLESS_API_PUBLIC_KEY" ]; then
+    echo "Atlas API public key must be provided via SERVERLESS_API_PUBLIC_KEY environment variable"
+    exit 1
+fi
+
+API_BASE_URL="https://account-dev.mongodb.com/api/private/nds/serverless/groups/$SERVERLESS_DRIVERS_GROUP"
+
+curl \
+  --silent \
+  --show-error \
+  -u "$SERVERLESS_API_PUBLIC_KEY:$SERVERLESS_API_PRIVATE_KEY" \
+  -X GET \
+  --digest \
+  --header "Accept: application/json" \
+  "${API_BASE_URL}/instances/${SERVERLESS_INSTANCE_NAME}?pretty=true" \
+
+echo ""
diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index db1db742b..ee2d45332 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -34,7 +34,14 @@ The `phpunit.xml.dist` file is used as the default configuration file for the
 test suite. In addition to various PHPUnit options, it defines required
 `MONGODB_URI` and `MONGODB_DATABASE` environment variables. You may customize
 this configuration by creating your own `phpunit.xml` file based on the
-`phpunit.xml.dist` file we provide.
+`phpunit.xml.dist` file we provide. To run the tests in serverless mode, set the
+`MONGODB_IS_SERVERLESS` environment variable to `on`.
+
+To run tests against a cluster that requires authentication, either include the
+credentials in the connection string given in the `MONGODB_URI` environment
+variable, or set the `MONGODB_USERNAME` and `MONGODB_PASSWORD` environment
+variables accordingly. Note that values defined through the environment override
+credentials present in the URI.
 
 By default, the `simple-phpunit` binary chooses the correct PHPUnit version for
 the PHP version you are running. To run tests against a specific PHPUnit version,
diff --git a/tests/Collection/CrudSpecFunctionalTest.php b/tests/Collection/CrudSpecFunctionalTest.php
index 398b6a4aa..f1cc519b6 100644
--- a/tests/Collection/CrudSpecFunctionalTest.php
+++ b/tests/Collection/CrudSpecFunctionalTest.php
@@ -32,10 +32,15 @@
  *
  * @see https://github.com/mongodb/specifications/tree/master/source/crud/tests
  *
+ * @group serverless
  * @group matrix-testing-exclude-server-5.0-driver-4.0
  */
 class CrudSpecFunctionalTest extends FunctionalTestCase
 {
+    public const SERVERLESS_ALLOW = 'allow';
+    public const SERVERLESS_FORBID = 'forbid';
+    public const SERVERLESS_REQUIRE = 'require';
+
     /** @var Collection */
     private $expectedCollection;
 
@@ -50,12 +55,14 @@ public function setUp(): void
     /**
      * @dataProvider provideSpecificationTests
      */
-    public function testSpecification(array $initialData, array $test, $minServerVersion, $maxServerVersion): void
+    public function testSpecification(array $initialData, array $test, $minServerVersion, $maxServerVersion, $serverless): void
     {
         if (isset($minServerVersion) || isset($maxServerVersion)) {
             $this->checkServerVersion($minServerVersion, $maxServerVersion);
         }
 
+        $this->checkServerlessRequirement($serverless);
+
         $expectedData = $test['outcome']['collection']['data'] ?? null;
         $this->initializeData($initialData, $expectedData);
 
@@ -83,12 +90,15 @@ public function provideSpecificationTests()
         foreach (glob(__DIR__ . '/spec-tests/*/*.json') as $filename) {
             $json = json_decode(file_get_contents($filename), true);
 
-            $minServerVersion = $json['minServerVersion'] ?? null;
-            $maxServerVersion = $json['maxServerVersion'] ?? null;
-
             foreach ($json['tests'] as $test) {
                 $name = str_replace(' ', '_', $test['description']);
-                $testArgs[$name] = [$json['data'], $test, $minServerVersion, $maxServerVersion];
+                $testArgs[$name] = [
+                    $json['data'],
+                    $test,
+                    $json['minServerVersion'] ?? null,
+                    $json['maxServerVersion'] ?? null,
+                    $json['serverless'] ?? null,
+                ];
             }
         }
 
@@ -113,6 +123,32 @@ private function assertEquivalentCollections(Collection $expectedCollection, Col
         }
     }
 
+    private function checkServerlessRequirement(?string $serverless): void
+    {
+        switch ($serverless) {
+            case null:
+            case self::SERVERLESS_ALLOW:
+                return;
+
+            case self::SERVERLESS_FORBID:
+                if ($this->isServerless()) {
+                    $this->markTestSkipped('Test does not apply on serverless');
+                }
+
+                return;
+
+            case self::SERVERLESS_REQUIRE:
+                if (! $this->isServerless()) {
+                    $this->markTestSkipped('Test requires serverless');
+                }
+
+                return;
+
+            default:
+                $this->fail(sprintf('Unknown serverless requirement "%s".', $serverless));
+        }
+    }
+
     /**
      * Checks that the server version is within the allowed bounds (if any).
      *
diff --git a/tests/Collection/spec-tests/read/aggregate-collation.json b/tests/Collection/spec-tests/read/aggregate-collation.json
index 85662a442..d958e447b 100644
--- a/tests/Collection/spec-tests/read/aggregate-collation.json
+++ b/tests/Collection/spec-tests/read/aggregate-collation.json
@@ -6,6 +6,7 @@
     }
   ],
   "minServerVersion": "3.4",
+  "serverless": "forbid",
   "tests": [
     {
       "description": "Aggregate with collation",
diff --git a/tests/Collection/spec-tests/read/aggregate-out.json b/tests/Collection/spec-tests/read/aggregate-out.json
index 205cf7657..c195e163e 100644
--- a/tests/Collection/spec-tests/read/aggregate-out.json
+++ b/tests/Collection/spec-tests/read/aggregate-out.json
@@ -14,6 +14,7 @@
     }
   ],
   "minServerVersion": "2.6",
+  "serverless": "forbid",
   "tests": [
     {
       "description": "Aggregate with $out",
@@ -41,16 +42,6 @@
         }
       },
       "outcome": {
-        "result": [
-          {
-            "_id": 2,
-            "x": 22
-          },
-          {
-            "_id": 3,
-            "x": 33
-          }
-        ],
         "collection": {
           "name": "other_test_collection",
           "data": [
@@ -92,16 +83,6 @@
         }
       },
       "outcome": {
-        "result": [
-          {
-            "_id": 2,
-            "x": 22
-          },
-          {
-            "_id": 3,
-            "x": 33
-          }
-        ],
         "collection": {
           "name": "other_test_collection",
           "data": [
diff --git a/tests/Collection/spec-tests/read/count-collation.json b/tests/Collection/spec-tests/read/count-collation.json
index 6f75282fe..7d6150849 100644
--- a/tests/Collection/spec-tests/read/count-collation.json
+++ b/tests/Collection/spec-tests/read/count-collation.json
@@ -6,6 +6,7 @@
     }
   ],
   "minServerVersion": "3.4",
+  "serverless": "forbid",
   "tests": [
     {
       "description": "Count documents with collation",
diff --git a/tests/Collection/spec-tests/read/distinct-collation.json b/tests/Collection/spec-tests/read/distinct-collation.json
index 0af0c67cb..984991a43 100644
--- a/tests/Collection/spec-tests/read/distinct-collation.json
+++ b/tests/Collection/spec-tests/read/distinct-collation.json
@@ -10,6 +10,7 @@
     }
   ],
   "minServerVersion": "3.4",
+  "serverless": "forbid",
   "tests": [
     {
       "description": "Distinct with a collation",
diff --git a/tests/Collection/spec-tests/read/find-collation.json b/tests/Collection/spec-tests/read/find-collation.json
index 53d0e9490..4e56c0525 100644
--- a/tests/Collection/spec-tests/read/find-collation.json
+++ b/tests/Collection/spec-tests/read/find-collation.json
@@ -6,6 +6,7 @@
     }
   ],
   "minServerVersion": "3.4",
+  "serverless": "forbid",
   "tests": [
     {
       "description": "Find with a collation",
diff --git a/tests/Collection/spec-tests/write/bulkWrite-collation.json b/tests/Collection/spec-tests/write/bulkWrite-collation.json
index 8e9d1bcb1..bc90aa817 100644
--- a/tests/Collection/spec-tests/write/bulkWrite-collation.json
+++ b/tests/Collection/spec-tests/write/bulkWrite-collation.json
@@ -22,6 +22,7 @@
     }
   ],
   "minServerVersion": "3.4",
+  "serverless": "forbid",
   "tests": [
     {
       "description": "BulkWrite with delete operations and collation",
diff --git a/tests/Collection/spec-tests/write/bulkWrite.json b/tests/Collection/spec-tests/write/bulkWrite.json
index 97879e7d3..dc00da28a 100644
--- a/tests/Collection/spec-tests/write/bulkWrite.json
+++ b/tests/Collection/spec-tests/write/bulkWrite.json
@@ -188,18 +188,6 @@
                 }
               }
             },
-            {
-              "name": "replaceOne",
-              "arguments": {
-                "filter": {
-                  "_id": 1
-                },
-                "replacement": {
-                  "_id": 1,
-                  "x": 11
-                }
-              }
-            },
             {
               "name": "replaceOne",
               "arguments": {
@@ -234,11 +222,11 @@
           "deletedCount": 0,
           "insertedCount": 0,
           "insertedIds": {},
-          "matchedCount": 2,
+          "matchedCount": 1,
           "modifiedCount": 1,
           "upsertedCount": 1,
           "upsertedIds": {
-            "3": 3
+            "2": 3
           }
         },
         "collection": {
diff --git a/tests/Collection/spec-tests/write/deleteMany-collation.json b/tests/Collection/spec-tests/write/deleteMany-collation.json
index d17bf3bcb..fce75e488 100644
--- a/tests/Collection/spec-tests/write/deleteMany-collation.json
+++ b/tests/Collection/spec-tests/write/deleteMany-collation.json
@@ -14,6 +14,7 @@
     }
   ],
   "minServerVersion": "3.4",
+  "serverless": "forbid",
   "tests": [
     {
       "description": "DeleteMany when many documents match with collation",
diff --git a/tests/Collection/spec-tests/write/deleteOne-collation.json b/tests/Collection/spec-tests/write/deleteOne-collation.json
index 2f7f92113..9bcef411e 100644
--- a/tests/Collection/spec-tests/write/deleteOne-collation.json
+++ b/tests/Collection/spec-tests/write/deleteOne-collation.json
@@ -14,6 +14,7 @@
     }
   ],
   "minServerVersion": "3.4",
+  "serverless": "forbid",
   "tests": [
     {
       "description": "DeleteOne when many documents matches with collation",
diff --git a/tests/Collection/spec-tests/write/findOneAndDelete-collation.json b/tests/Collection/spec-tests/write/findOneAndDelete-collation.json
index 1ff37d2e8..32480da84 100644
--- a/tests/Collection/spec-tests/write/findOneAndDelete-collation.json
+++ b/tests/Collection/spec-tests/write/findOneAndDelete-collation.json
@@ -14,6 +14,7 @@
     }
   ],
   "minServerVersion": "3.4",
+  "serverless": "forbid",
   "tests": [
     {
       "description": "FindOneAndDelete when one document matches with collation",
diff --git a/tests/Collection/spec-tests/write/findOneAndReplace-collation.json b/tests/Collection/spec-tests/write/findOneAndReplace-collation.json
index babb2f7c1..9b3c25005 100644
--- a/tests/Collection/spec-tests/write/findOneAndReplace-collation.json
+++ b/tests/Collection/spec-tests/write/findOneAndReplace-collation.json
@@ -10,6 +10,7 @@
     }
   ],
   "minServerVersion": "3.4",
+  "serverless": "forbid",
   "tests": [
     {
       "description": "FindOneAndReplace when one document matches with collation returning the document after modification",
diff --git a/tests/Collection/spec-tests/write/findOneAndUpdate-collation.json b/tests/Collection/spec-tests/write/findOneAndUpdate-collation.json
index 04c1fe73e..8abab7bd6 100644
--- a/tests/Collection/spec-tests/write/findOneAndUpdate-collation.json
+++ b/tests/Collection/spec-tests/write/findOneAndUpdate-collation.json
@@ -14,6 +14,7 @@
     }
   ],
   "minServerVersion": "3.4",
+  "serverless": "forbid",
   "tests": [
     {
       "description": "FindOneAndUpdate when many documents match with collation returning the document before modification",
diff --git a/tests/Collection/spec-tests/write/replaceOne-collation.json b/tests/Collection/spec-tests/write/replaceOne-collation.json
index a668fe738..fa4cbe997 100644
--- a/tests/Collection/spec-tests/write/replaceOne-collation.json
+++ b/tests/Collection/spec-tests/write/replaceOne-collation.json
@@ -10,6 +10,7 @@
     }
   ],
   "minServerVersion": "3.4",
+  "serverless": "forbid",
   "tests": [
     {
       "description": "ReplaceOne when one document matches with collation",
diff --git a/tests/Collection/spec-tests/write/updateMany-collation.json b/tests/Collection/spec-tests/write/updateMany-collation.json
index 3cb49f229..8becfd806 100644
--- a/tests/Collection/spec-tests/write/updateMany-collation.json
+++ b/tests/Collection/spec-tests/write/updateMany-collation.json
@@ -14,6 +14,7 @@
     }
   ],
   "minServerVersion": "3.4",
+  "serverless": "forbid",
   "tests": [
     {
       "description": "UpdateMany when many documents match with collation",
diff --git a/tests/Collection/spec-tests/write/updateOne-collation.json b/tests/Collection/spec-tests/write/updateOne-collation.json
index c49112d51..3afdb83e0 100644
--- a/tests/Collection/spec-tests/write/updateOne-collation.json
+++ b/tests/Collection/spec-tests/write/updateOne-collation.json
@@ -10,6 +10,7 @@
     }
   ],
   "minServerVersion": "3.4",
+  "serverless": "forbid",
   "tests": [
     {
       "description": "UpdateOne when one document matches with collation",
diff --git a/tests/FunctionalTestCase.php b/tests/FunctionalTestCase.php
index 38877c92b..3a70f34ff 100644
--- a/tests/FunctionalTestCase.php
+++ b/tests/FunctionalTestCase.php
@@ -25,6 +25,7 @@
 use function count;
 use function current;
 use function explode;
+use function filter_var;
 use function getenv;
 use function implode;
 use function is_array;
@@ -42,6 +43,7 @@
 use function sprintf;
 use function version_compare;
 
+use const FILTER_VALIDATE_BOOLEAN;
 use const INFO_MODULES;
 
 abstract class FunctionalTestCase extends TestCase
@@ -69,12 +71,20 @@ public function tearDown(): void
 
     public static function createTestClient(?string $uri = null, array $options = [], array $driverOptions = []): Client
     {
-        return new Client($uri ?? static::getUri(), $options, static::appendServerApiOption($driverOptions));
+        return new Client(
+            $uri ?? static::getUri(),
+            static::appendAuthenticationOptions($options),
+            static::appendServerApiOption($driverOptions)
+        );
     }
 
     public static function createTestManager(?string $uri = null, array $options = [], array $driverOptions = []): Manager
     {
-        return new Manager($uri ?? static::getUri(), $options, static::appendServerApiOption($driverOptions));
+        return new Manager(
+            $uri ?? static::getUri(),
+            static::appendAuthenticationOptions($options),
+            static::appendServerApiOption($driverOptions)
+        );
     }
 
     public static function getUri($allowMultipleMongoses = false): string
@@ -385,6 +395,16 @@ protected function isReplicaSet()
         return $this->getPrimaryServer()->getType() == Server::TYPE_RS_PRIMARY;
     }
 
+    /**
+     * Return whether serverless (i.e. proxy as mongos) is being utilized.
+     */
+    protected static function isServerless(): bool
+    {
+        $isServerless = getenv('MONGODB_IS_SERVERLESS');
+
+        return $isServerless !== false ? filter_var($isServerless, FILTER_VALIDATE_BOOLEAN) : false;
+    }
+
     protected function isShardedCluster()
     {
         return $this->getPrimaryServer()->getType() == Server::TYPE_MONGOS;
@@ -513,6 +533,26 @@ protected function skipIfTransactionsAreNotSupported(): void
         }
     }
 
+    private static function appendAuthenticationOptions(array $options): array
+    {
+        if (isset($options['username']) || isset($options['password'])) {
+            return $options;
+        }
+
+        $username = getenv('MONGODB_USERNAME') ?: null;
+        $password = getenv('MONGODB_PASSWORD') ?: null;
+
+        if ($username !== null) {
+            $options['username'] = $username;
+        }
+
+        if ($password !== null) {
+            $options['password'] = $password;
+        }
+
+        return $options;
+    }
+
     private static function appendServerApiOption(array $driverOptions): array
     {
         if (getenv('API_VERSION') && ! isset($driverOptions['serverApi'])) {
diff --git a/tests/SpecTests/FunctionalTestCase.php b/tests/SpecTests/FunctionalTestCase.php
index 9c6939639..d9738c568 100644
--- a/tests/SpecTests/FunctionalTestCase.php
+++ b/tests/SpecTests/FunctionalTestCase.php
@@ -30,6 +30,10 @@ class FunctionalTestCase extends BaseFunctionalTestCase
     public const TOPOLOGY_REPLICASET = 'replicaset';
     public const TOPOLOGY_SHARDED = 'sharded';
 
+    public const SERVERLESS_ALLOW = 'allow';
+    public const SERVERLESS_FORBID = 'forbid';
+    public const SERVERLESS_REQUIRE = 'require';
+
     /** @var Context|null */
     private $context;
 
@@ -137,8 +141,9 @@ protected function checkServerRequirements(array $runOn): void
             $minServerVersion = $req->minServerVersion ?? null;
             $maxServerVersion = $req->maxServerVersion ?? null;
             $topologies = $req->topology ?? null;
+            $serverlessMode = $req->serverless ?? null;
 
-            if ($this->isServerRequirementSatisifed($minServerVersion, $maxServerVersion, $topologies)) {
+            if ($this->isServerRequirementSatisifed($minServerVersion, $maxServerVersion, $topologies, $serverlessMode)) {
                 return;
             }
         }
@@ -268,7 +273,27 @@ private function getTopology(): string
             return $topologyTypeMap[$primaryType];
         }
 
-        throw new UnexpectedValueException('Toplogy is neither single nor RS nor sharded');
+        throw new UnexpectedValueException(sprintf('Cannot find topology for primary of type "%s".', $primaryType));
+    }
+
+    private function isServerlessRequirementSatisfied(?string $serverlessMode): bool
+    {
+        if ($serverlessMode === null) {
+            return true;
+        }
+
+        switch ($serverlessMode) {
+            case self::SERVERLESS_ALLOW:
+                return true;
+
+            case self::SERVERLESS_FORBID:
+                return ! static::isServerless();
+
+            case self::SERVERLESS_REQUIRE:
+                return static::isServerless();
+        }
+
+        throw new UnexpectedValueException(sprintf('Invalid serverless requirement "%s" found.', $serverlessMode));
     }
 
     /**
@@ -279,7 +304,7 @@ private function getTopology(): string
      * @param array|null  $topologies
      * @return boolean
      */
-    private function isServerRequirementSatisifed(?string $minServerVersion, ?string $maxServerVersion, ?array $topologies = null): bool
+    private function isServerRequirementSatisifed(?string $minServerVersion, ?string $maxServerVersion, ?array $topologies = null, ?string $serverlessMode = null): bool
     {
         $serverVersion = $this->getServerVersion();
 
@@ -297,6 +322,10 @@ private function isServerRequirementSatisifed(?string $minServerVersion, ?string
             return false;
         }
 
+        if (! $this->isServerlessRequirementSatisfied($serverlessMode)) {
+            return false;
+        }
+
         return true;
     }
 }
diff --git a/tests/SpecTests/RetryableReadsSpecTest.php b/tests/SpecTests/RetryableReadsSpecTest.php
index 3f16f4324..1498a34b2 100644
--- a/tests/SpecTests/RetryableReadsSpecTest.php
+++ b/tests/SpecTests/RetryableReadsSpecTest.php
@@ -14,6 +14,7 @@
  * Retryable reads spec tests.
  *
  * @see https://github.com/mongodb/specifications/tree/master/source/retryable-reads
+ * @group serverless
  */
 class RetryableReadsSpecTest extends FunctionalTestCase
 {
@@ -24,6 +25,9 @@ class RetryableReadsSpecTest extends FunctionalTestCase
         'listIndexNames' => 'Not implemented',
     ];
 
+    /** @var array */
+    private static $incompleteTests = ['mapReduce: MapReduce succeeds with retry on' => 'PHPLIB-715'];
+
     /**
      * Assert that the expected and actual command documents match.
      *
@@ -65,6 +69,10 @@ public function testRetryableReads(stdClass $test, ?array $runOn = null, $data,
             $this->skipIfChangeStreamIsNotSupported();
         }
 
+        if (isset(self::$incompleteTests[$this->dataDescription()])) {
+            $this->markTestIncomplete(self::$incompleteTests[$this->dataDescription()]);
+        }
+
         $context = Context::fromRetryableReads($test, $databaseName, $collectionName, $bucketName);
         $this->setContext($context);
 
diff --git a/tests/SpecTests/RetryableWritesSpecTest.php b/tests/SpecTests/RetryableWritesSpecTest.php
index 8f9ffaf97..aa9f9083d 100644
--- a/tests/SpecTests/RetryableWritesSpecTest.php
+++ b/tests/SpecTests/RetryableWritesSpecTest.php
@@ -12,6 +12,7 @@
  * Retryable writes spec tests.
  *
  * @see https://github.com/mongodb/specifications/tree/master/source/retryable-writes
+ * @group serverless
  */
 class RetryableWritesSpecTest extends FunctionalTestCase
 {
diff --git a/tests/SpecTests/TransactionsSpecTest.php b/tests/SpecTests/TransactionsSpecTest.php
index 1829ed6a1..165f3c255 100644
--- a/tests/SpecTests/TransactionsSpecTest.php
+++ b/tests/SpecTests/TransactionsSpecTest.php
@@ -110,17 +110,43 @@ public static function assertCommandMatches(stdClass $expected, stdClass $actual
         static::assertDocumentsMatch($expected, $actual);
     }
 
+    /**
+     * @dataProvider provideTransactionsTests
+     * @group serverless
+     */
+    public function testTransactions(stdClass $test, ?array $runOn = null, array $data, ?string $databaseName = null, ?string $collectionName = null): void
+    {
+        $this->runTransactionTest($test, $runOn, $data, $databaseName, $collectionName);
+    }
+
+    public function provideTransactionsTests(): array
+    {
+        return $this->provideTests('transactions');
+    }
+
+    /**
+     * @dataProvider provideTransactionsConvenientApiTests
+     */
+    public function testTransactionsConvenientApi(stdClass $test, ?array $runOn = null, array $data, ?string $databaseName = null, ?string $collectionName = null): void
+    {
+        $this->runTransactionTest($test, $runOn, $data, $databaseName, $collectionName);
+    }
+
+    public function provideTransactionsConvenientApiTests(): array
+    {
+        return $this->provideTests('transactions-convenient-api');
+    }
+
     /**
      * Execute an individual test case from the specification.
      *
-     * @dataProvider provideTests
      * @param stdClass $test           Individual "tests[]" document
      * @param array    $runOn          Top-level "runOn" array with server requirements
      * @param array    $data           Top-level "data" array to initialize collection
      * @param string   $databaseName   Name of database under test
      * @param string   $collectionName Name of collection under test
      */
-    public function testTransactions(stdClass $test, ?array $runOn = null, array $data, ?string $databaseName = null, ?string $collectionName = null): void
+    private function runTransactionTest(stdClass $test, ?array $runOn = null, array $data, ?string $databaseName = null, ?string $collectionName = null): void
     {
         if (isset(self::$incompleteTests[$this->dataDescription()])) {
             $this->markTestIncomplete(self::$incompleteTests[$this->dataDescription()]);
@@ -173,11 +199,11 @@ public function testTransactions(stdClass $test, ?array $runOn = null, array $da
         }
     }
 
-    public function provideTests()
+    private function provideTests(string $dir): array
     {
         $testArgs = [];
 
-        foreach (glob(__DIR__ . '/transactions*/*.json') as $filename) {
+        foreach (glob(__DIR__ . '/' . $dir . '/*.json') as $filename) {
             $json = $this->decodeJson(file_get_contents($filename));
             $group = basename(dirname($filename)) . '/' . basename($filename, '.json');
             $runOn = $json->runOn ?? null;
@@ -290,6 +316,11 @@ protected function createTestCollection(): void
      */
     private static function killAllSessions(): void
     {
+        // killAllSessions is not supported on serverless, see CLOUDP-84298
+        if (static::isServerless()) {
+            return;
+        }
+
         $manager = static::createTestManager();
         $primary = $manager->selectServer(new ReadPreference('primary'));
 
diff --git a/tests/SpecTests/retryable-reads/aggregate-serverErrors.json b/tests/SpecTests/retryable-reads/aggregate-serverErrors.json
index f6197cc9f..1155f808d 100644
--- a/tests/SpecTests/retryable-reads/aggregate-serverErrors.json
+++ b/tests/SpecTests/retryable-reads/aggregate-serverErrors.json
@@ -10,7 +10,8 @@
     {
       "minServerVersion": "4.1.7",
       "topology": [
-        "sharded"
+        "sharded",
+        "load-balanced"
       ]
     }
   ],
diff --git a/tests/SpecTests/retryable-reads/aggregate.json b/tests/SpecTests/retryable-reads/aggregate.json
index 30a6e05e6..f23d5c679 100644
--- a/tests/SpecTests/retryable-reads/aggregate.json
+++ b/tests/SpecTests/retryable-reads/aggregate.json
@@ -10,7 +10,8 @@
     {
       "minServerVersion": "4.1.7",
       "topology": [
-        "sharded"
+        "sharded",
+        "load-balanced"
       ]
     }
   ],
diff --git a/tests/SpecTests/retryable-reads/changeStreams-client.watch-serverErrors.json b/tests/SpecTests/retryable-reads/changeStreams-client.watch-serverErrors.json
index f67ee8d30..73dbfee91 100644
--- a/tests/SpecTests/retryable-reads/changeStreams-client.watch-serverErrors.json
+++ b/tests/SpecTests/retryable-reads/changeStreams-client.watch-serverErrors.json
@@ -9,8 +9,10 @@
     {
       "minServerVersion": "4.1.7",
       "topology": [
-        "sharded"
-      ]
+        "sharded",
+        "load-balanced"
+      ],
+      "serverless": "forbid"
     }
   ],
   "database_name": "retryable-reads-tests",
diff --git a/tests/SpecTests/retryable-reads/changeStreams-client.watch.json b/tests/SpecTests/retryable-reads/changeStreams-client.watch.json
index 9a2ccad09..30a53037a 100644
--- a/tests/SpecTests/retryable-reads/changeStreams-client.watch.json
+++ b/tests/SpecTests/retryable-reads/changeStreams-client.watch.json
@@ -9,8 +9,10 @@
     {
       "minServerVersion": "4.1.7",
       "topology": [
-        "sharded"
-      ]
+        "sharded",
+        "load-balanced"
+      ],
+      "serverless": "forbid"
     }
   ],
   "database_name": "retryable-reads-tests",
diff --git a/tests/SpecTests/retryable-reads/changeStreams-db.coll.watch-serverErrors.json b/tests/SpecTests/retryable-reads/changeStreams-db.coll.watch-serverErrors.json
index 63514f6a8..77b3af04f 100644
--- a/tests/SpecTests/retryable-reads/changeStreams-db.coll.watch-serverErrors.json
+++ b/tests/SpecTests/retryable-reads/changeStreams-db.coll.watch-serverErrors.json
@@ -9,8 +9,10 @@
     {
       "minServerVersion": "4.1.7",
       "topology": [
-        "sharded"
-      ]
+        "sharded",
+        "load-balanced"
+      ],
+      "serverless": "forbid"
     }
   ],
   "database_name": "retryable-reads-tests",
diff --git a/tests/SpecTests/retryable-reads/changeStreams-db.coll.watch.json b/tests/SpecTests/retryable-reads/changeStreams-db.coll.watch.json
index 3408c8423..27f6105a4 100644
--- a/tests/SpecTests/retryable-reads/changeStreams-db.coll.watch.json
+++ b/tests/SpecTests/retryable-reads/changeStreams-db.coll.watch.json
@@ -9,8 +9,10 @@
     {
       "minServerVersion": "4.1.7",
       "topology": [
-        "sharded"
-      ]
+        "sharded",
+        "load-balanced"
+      ],
+      "serverless": "forbid"
     }
   ],
   "database_name": "retryable-reads-tests",
diff --git a/tests/SpecTests/retryable-reads/changeStreams-db.watch-serverErrors.json b/tests/SpecTests/retryable-reads/changeStreams-db.watch-serverErrors.json
index 8d1624240..7a8753450 100644
--- a/tests/SpecTests/retryable-reads/changeStreams-db.watch-serverErrors.json
+++ b/tests/SpecTests/retryable-reads/changeStreams-db.watch-serverErrors.json
@@ -9,8 +9,10 @@
     {
       "minServerVersion": "4.1.7",
       "topology": [
-        "sharded"
-      ]
+        "sharded",
+        "load-balanced"
+      ],
+      "serverless": "forbid"
     }
   ],
   "database_name": "retryable-reads-tests",
diff --git a/tests/SpecTests/retryable-reads/changeStreams-db.watch.json b/tests/SpecTests/retryable-reads/changeStreams-db.watch.json
index bec09c49b..e6b0b9b78 100644
--- a/tests/SpecTests/retryable-reads/changeStreams-db.watch.json
+++ b/tests/SpecTests/retryable-reads/changeStreams-db.watch.json
@@ -9,8 +9,10 @@
     {
       "minServerVersion": "4.1.7",
       "topology": [
-        "sharded"
-      ]
+        "sharded",
+        "load-balanced"
+      ],
+      "serverless": "forbid"
     }
   ],
   "database_name": "retryable-reads-tests",
diff --git a/tests/SpecTests/retryable-reads/count-serverErrors.json b/tests/SpecTests/retryable-reads/count-serverErrors.json
index 1de695eb8..36a0c17ca 100644
--- a/tests/SpecTests/retryable-reads/count-serverErrors.json
+++ b/tests/SpecTests/retryable-reads/count-serverErrors.json
@@ -10,7 +10,8 @@
     {
       "minServerVersion": "4.1.7",
       "topology": [
-        "sharded"
+        "sharded",
+        "load-balanced"
       ]
     }
   ],
diff --git a/tests/SpecTests/retryable-reads/count.json b/tests/SpecTests/retryable-reads/count.json
index 0ccf4982b..139a54513 100644
--- a/tests/SpecTests/retryable-reads/count.json
+++ b/tests/SpecTests/retryable-reads/count.json
@@ -10,7 +10,8 @@
     {
       "minServerVersion": "4.1.7",
       "topology": [
-        "sharded"
+        "sharded",
+        "load-balanced"
       ]
     }
   ],
diff --git a/tests/SpecTests/retryable-reads/countDocuments-serverErrors.json b/tests/SpecTests/retryable-reads/countDocuments-serverErrors.json
index 8e7a1b58e..782ea5e4f 100644
--- a/tests/SpecTests/retryable-reads/countDocuments-serverErrors.json
+++ b/tests/SpecTests/retryable-reads/countDocuments-serverErrors.json
@@ -10,7 +10,8 @@
     {
       "minServerVersion": "4.1.7",
       "topology": [
-        "sharded"
+        "sharded",
+        "load-balanced"
       ]
     }
   ],
diff --git a/tests/SpecTests/retryable-reads/countDocuments.json b/tests/SpecTests/retryable-reads/countDocuments.json
index b4ccf3668..57a64e45b 100644
--- a/tests/SpecTests/retryable-reads/countDocuments.json
+++ b/tests/SpecTests/retryable-reads/countDocuments.json
@@ -10,7 +10,8 @@
     {
       "minServerVersion": "4.1.7",
       "topology": [
-        "sharded"
+        "sharded",
+        "load-balanced"
       ]
     }
   ],
diff --git a/tests/SpecTests/retryable-reads/distinct-serverErrors.json b/tests/SpecTests/retryable-reads/distinct-serverErrors.json
index c168b37ec..d7c6018a6 100644
--- a/tests/SpecTests/retryable-reads/distinct-serverErrors.json
+++ b/tests/SpecTests/retryable-reads/distinct-serverErrors.json
@@ -10,7 +10,8 @@
     {
       "minServerVersion": "4.1.7",
       "topology": [
-        "sharded"
+        "sharded",
+        "load-balanced"
       ]
     }
   ],
diff --git a/tests/SpecTests/retryable-reads/distinct.json b/tests/SpecTests/retryable-reads/distinct.json
index b5885e27e..1fd415da8 100644
--- a/tests/SpecTests/retryable-reads/distinct.json
+++ b/tests/SpecTests/retryable-reads/distinct.json
@@ -10,7 +10,8 @@
     {
       "minServerVersion": "4.1.7",
       "topology": [
-        "sharded"
+        "sharded",
+        "load-balanced"
       ]
     }
   ],
diff --git a/tests/SpecTests/retryable-reads/find-serverErrors.json b/tests/SpecTests/retryable-reads/find-serverErrors.json
index 3d1cfa456..f6b96c6dc 100644
--- a/tests/SpecTests/retryable-reads/find-serverErrors.json
+++ b/tests/SpecTests/retryable-reads/find-serverErrors.json
@@ -10,7 +10,8 @@
     {
       "minServerVersion": "4.1.7",
       "topology": [
-        "sharded"
+        "sharded",
+        "load-balanced"
       ]
     }
   ],
diff --git a/tests/SpecTests/retryable-reads/find.json b/tests/SpecTests/retryable-reads/find.json
index 56479ff1d..00d419c0d 100644
--- a/tests/SpecTests/retryable-reads/find.json
+++ b/tests/SpecTests/retryable-reads/find.json
@@ -10,7 +10,8 @@
     {
       "minServerVersion": "4.1.7",
       "topology": [
-        "sharded"
+        "sharded",
+        "load-balanced"
       ]
     }
   ],
diff --git a/tests/SpecTests/retryable-reads/findOne-serverErrors.json b/tests/SpecTests/retryable-reads/findOne-serverErrors.json
index 161dc42f3..d039ef247 100644
--- a/tests/SpecTests/retryable-reads/findOne-serverErrors.json
+++ b/tests/SpecTests/retryable-reads/findOne-serverErrors.json
@@ -10,7 +10,8 @@
     {
       "minServerVersion": "4.1.7",
       "topology": [
-        "sharded"
+        "sharded",
+        "load-balanced"
       ]
     }
   ],
diff --git a/tests/SpecTests/retryable-reads/findOne.json b/tests/SpecTests/retryable-reads/findOne.json
index d296a9cdb..b9deb73d2 100644
--- a/tests/SpecTests/retryable-reads/findOne.json
+++ b/tests/SpecTests/retryable-reads/findOne.json
@@ -10,7 +10,8 @@
     {
       "minServerVersion": "4.1.7",
       "topology": [
-        "sharded"
+        "sharded",
+        "load-balanced"
       ]
     }
   ],
diff --git a/tests/SpecTests/retryable-reads/gridfs-download-serverErrors.json b/tests/SpecTests/retryable-reads/gridfs-download-serverErrors.json
index af091d679..cec3a5016 100644
--- a/tests/SpecTests/retryable-reads/gridfs-download-serverErrors.json
+++ b/tests/SpecTests/retryable-reads/gridfs-download-serverErrors.json
@@ -10,7 +10,8 @@
     {
       "minServerVersion": "4.1.7",
       "topology": [
-        "sharded"
+        "sharded",
+        "load-balanced"
       ]
     }
   ],
diff --git a/tests/SpecTests/retryable-reads/gridfs-download.json b/tests/SpecTests/retryable-reads/gridfs-download.json
index a5c5ef4d5..4d0d5a17e 100644
--- a/tests/SpecTests/retryable-reads/gridfs-download.json
+++ b/tests/SpecTests/retryable-reads/gridfs-download.json
@@ -10,7 +10,8 @@
     {
       "minServerVersion": "4.1.7",
       "topology": [
-        "sharded"
+        "sharded",
+        "load-balanced"
       ]
     }
   ],
diff --git a/tests/SpecTests/retryable-reads/gridfs-downloadByName-serverErrors.json b/tests/SpecTests/retryable-reads/gridfs-downloadByName-serverErrors.json
index 61e3a5947..a64230d38 100644
--- a/tests/SpecTests/retryable-reads/gridfs-downloadByName-serverErrors.json
+++ b/tests/SpecTests/retryable-reads/gridfs-downloadByName-serverErrors.json
@@ -10,7 +10,8 @@
     {
       "minServerVersion": "4.1.7",
       "topology": [
-        "sharded"
+        "sharded",
+        "load-balanced"
       ]
     }
   ],
diff --git a/tests/SpecTests/retryable-reads/gridfs-downloadByName.json b/tests/SpecTests/retryable-reads/gridfs-downloadByName.json
index 0634a09bf..48f2168cf 100644
--- a/tests/SpecTests/retryable-reads/gridfs-downloadByName.json
+++ b/tests/SpecTests/retryable-reads/gridfs-downloadByName.json
@@ -10,7 +10,8 @@
     {
       "minServerVersion": "4.1.7",
       "topology": [
-        "sharded"
+        "sharded",
+        "load-balanced"
       ]
     }
   ],
diff --git a/tests/SpecTests/retryable-reads/listCollectionNames-serverErrors.json b/tests/SpecTests/retryable-reads/listCollectionNames-serverErrors.json
index a07e746a5..bbdce625a 100644
--- a/tests/SpecTests/retryable-reads/listCollectionNames-serverErrors.json
+++ b/tests/SpecTests/retryable-reads/listCollectionNames-serverErrors.json
@@ -10,7 +10,8 @@
     {
       "minServerVersion": "4.1.7",
       "topology": [
-        "sharded"
+        "sharded",
+        "load-balanced"
       ]
     }
   ],
diff --git a/tests/SpecTests/retryable-reads/listCollectionNames.json b/tests/SpecTests/retryable-reads/listCollectionNames.json
index 437fc36a4..73d96a3cf 100644
--- a/tests/SpecTests/retryable-reads/listCollectionNames.json
+++ b/tests/SpecTests/retryable-reads/listCollectionNames.json
@@ -10,7 +10,8 @@
     {
       "minServerVersion": "4.1.7",
       "topology": [
-        "sharded"
+        "sharded",
+        "load-balanced"
       ]
     }
   ],
diff --git a/tests/SpecTests/retryable-reads/listCollectionObjects-serverErrors.json b/tests/SpecTests/retryable-reads/listCollectionObjects-serverErrors.json
index c2d4358fb..ab469dfe3 100644
--- a/tests/SpecTests/retryable-reads/listCollectionObjects-serverErrors.json
+++ b/tests/SpecTests/retryable-reads/listCollectionObjects-serverErrors.json
@@ -10,7 +10,8 @@
     {
       "minServerVersion": "4.1.7",
       "topology": [
-        "sharded"
+        "sharded",
+        "load-balanced"
       ]
     }
   ],
diff --git a/tests/SpecTests/retryable-reads/listCollectionObjects.json b/tests/SpecTests/retryable-reads/listCollectionObjects.json
index 1f537b743..1fb0f1843 100644
--- a/tests/SpecTests/retryable-reads/listCollectionObjects.json
+++ b/tests/SpecTests/retryable-reads/listCollectionObjects.json
@@ -10,7 +10,8 @@
     {
       "minServerVersion": "4.1.7",
       "topology": [
-        "sharded"
+        "sharded",
+        "load-balanced"
       ]
     }
   ],
diff --git a/tests/SpecTests/retryable-reads/listCollections-serverErrors.json b/tests/SpecTests/retryable-reads/listCollections-serverErrors.json
index f749c8c27..def9ac459 100644
--- a/tests/SpecTests/retryable-reads/listCollections-serverErrors.json
+++ b/tests/SpecTests/retryable-reads/listCollections-serverErrors.json
@@ -10,7 +10,8 @@
     {
       "minServerVersion": "4.1.7",
       "topology": [
-        "sharded"
+        "sharded",
+        "load-balanced"
       ]
     }
   ],
diff --git a/tests/SpecTests/retryable-reads/listCollections.json b/tests/SpecTests/retryable-reads/listCollections.json
index a6b452e64..242788362 100644
--- a/tests/SpecTests/retryable-reads/listCollections.json
+++ b/tests/SpecTests/retryable-reads/listCollections.json
@@ -10,7 +10,8 @@
     {
       "minServerVersion": "4.1.7",
       "topology": [
-        "sharded"
+        "sharded",
+        "load-balanced"
       ]
     }
   ],
diff --git a/tests/SpecTests/retryable-reads/listDatabaseNames-serverErrors.json b/tests/SpecTests/retryable-reads/listDatabaseNames-serverErrors.json
index 959d70fb3..1dd8e4415 100644
--- a/tests/SpecTests/retryable-reads/listDatabaseNames-serverErrors.json
+++ b/tests/SpecTests/retryable-reads/listDatabaseNames-serverErrors.json
@@ -10,7 +10,8 @@
     {
       "minServerVersion": "4.1.7",
       "topology": [
-        "sharded"
+        "sharded",
+        "load-balanced"
       ]
     }
   ],
diff --git a/tests/SpecTests/retryable-reads/listDatabaseNames.json b/tests/SpecTests/retryable-reads/listDatabaseNames.json
index b35f7ab18..b431f5701 100644
--- a/tests/SpecTests/retryable-reads/listDatabaseNames.json
+++ b/tests/SpecTests/retryable-reads/listDatabaseNames.json
@@ -10,7 +10,8 @@
     {
       "minServerVersion": "4.1.7",
       "topology": [
-        "sharded"
+        "sharded",
+        "load-balanced"
       ]
     }
   ],
diff --git a/tests/SpecTests/retryable-reads/listDatabaseObjects-serverErrors.json b/tests/SpecTests/retryable-reads/listDatabaseObjects-serverErrors.json
index 6b95b421a..bc497bb08 100644
--- a/tests/SpecTests/retryable-reads/listDatabaseObjects-serverErrors.json
+++ b/tests/SpecTests/retryable-reads/listDatabaseObjects-serverErrors.json
@@ -10,7 +10,8 @@
     {
       "minServerVersion": "4.1.7",
       "topology": [
-        "sharded"
+        "sharded",
+        "load-balanced"
       ]
     }
   ],
diff --git a/tests/SpecTests/retryable-reads/listDatabaseObjects.json b/tests/SpecTests/retryable-reads/listDatabaseObjects.json
index cbd2c6763..267fe921c 100644
--- a/tests/SpecTests/retryable-reads/listDatabaseObjects.json
+++ b/tests/SpecTests/retryable-reads/listDatabaseObjects.json
@@ -10,7 +10,8 @@
     {
       "minServerVersion": "4.1.7",
       "topology": [
-        "sharded"
+        "sharded",
+        "load-balanced"
       ]
     }
   ],
diff --git a/tests/SpecTests/retryable-reads/listDatabases-serverErrors.json b/tests/SpecTests/retryable-reads/listDatabases-serverErrors.json
index 1393f5f89..ed7bcbc39 100644
--- a/tests/SpecTests/retryable-reads/listDatabases-serverErrors.json
+++ b/tests/SpecTests/retryable-reads/listDatabases-serverErrors.json
@@ -10,7 +10,8 @@
     {
       "minServerVersion": "4.1.7",
       "topology": [
-        "sharded"
+        "sharded",
+        "load-balanced"
       ]
     }
   ],
diff --git a/tests/SpecTests/retryable-reads/listDatabases.json b/tests/SpecTests/retryable-reads/listDatabases.json
index 3cb8bbd08..69ef9788f 100644
--- a/tests/SpecTests/retryable-reads/listDatabases.json
+++ b/tests/SpecTests/retryable-reads/listDatabases.json
@@ -10,7 +10,8 @@
     {
       "minServerVersion": "4.1.7",
       "topology": [
-        "sharded"
+        "sharded",
+        "load-balanced"
       ]
     }
   ],
diff --git a/tests/SpecTests/retryable-reads/listIndexNames-serverErrors.json b/tests/SpecTests/retryable-reads/listIndexNames-serverErrors.json
index 04d60f100..2d3265ec8 100644
--- a/tests/SpecTests/retryable-reads/listIndexNames-serverErrors.json
+++ b/tests/SpecTests/retryable-reads/listIndexNames-serverErrors.json
@@ -10,7 +10,8 @@
     {
       "minServerVersion": "4.1.7",
       "topology": [
-        "sharded"
+        "sharded",
+        "load-balanced"
       ]
     }
   ],
diff --git a/tests/SpecTests/retryable-reads/listIndexNames.json b/tests/SpecTests/retryable-reads/listIndexNames.json
index 912c70601..fbdb420f8 100644
--- a/tests/SpecTests/retryable-reads/listIndexNames.json
+++ b/tests/SpecTests/retryable-reads/listIndexNames.json
@@ -10,7 +10,8 @@
     {
       "minServerVersion": "4.1.7",
       "topology": [
-        "sharded"
+        "sharded",
+        "load-balanced"
       ]
     }
   ],
diff --git a/tests/SpecTests/retryable-reads/listIndexes-serverErrors.json b/tests/SpecTests/retryable-reads/listIndexes-serverErrors.json
index ccf385c5b..25c5b0e44 100644
--- a/tests/SpecTests/retryable-reads/listIndexes-serverErrors.json
+++ b/tests/SpecTests/retryable-reads/listIndexes-serverErrors.json
@@ -10,7 +10,8 @@
     {
       "minServerVersion": "4.1.7",
       "topology": [
-        "sharded"
+        "sharded",
+        "load-balanced"
       ]
     }
   ],
diff --git a/tests/SpecTests/retryable-reads/listIndexes.json b/tests/SpecTests/retryable-reads/listIndexes.json
index f460ea768..5cb620ae4 100644
--- a/tests/SpecTests/retryable-reads/listIndexes.json
+++ b/tests/SpecTests/retryable-reads/listIndexes.json
@@ -10,7 +10,8 @@
     {
       "minServerVersion": "4.1.7",
       "topology": [
-        "sharded"
+        "sharded",
+        "load-balanced"
       ]
     }
   ],
diff --git a/tests/SpecTests/retryable-reads/mapReduce.json b/tests/SpecTests/retryable-reads/mapReduce.json
index 3cb35fd49..9327a2305 100644
--- a/tests/SpecTests/retryable-reads/mapReduce.json
+++ b/tests/SpecTests/retryable-reads/mapReduce.json
@@ -10,8 +10,10 @@
     {
       "minServerVersion": "4.1.7",
       "topology": [
-        "sharded"
-      ]
+        "sharded",
+        "load-balanced"
+      ],
+      "serverless": "forbid"
     }
   ],
   "database_name": "retryable-reads-tests",
@@ -50,8 +52,8 @@
           },
           "result": [
             {
-              "_id": 0.0,
-              "value": 6.0
+              "_id": 0,
+              "value": 6
             }
           ]
         }
diff --git a/tests/SpecTests/retryable-writes/bulkWrite-errorLabels.json b/tests/SpecTests/retryable-writes/bulkWrite-errorLabels.json
index 94ea3ea98..66c3ecb33 100644
--- a/tests/SpecTests/retryable-writes/bulkWrite-errorLabels.json
+++ b/tests/SpecTests/retryable-writes/bulkWrite-errorLabels.json
@@ -4,7 +4,8 @@
       "minServerVersion": "4.3.1",
       "topology": [
         "replicaset",
-        "sharded"
+        "sharded",
+        "load-balanced"
       ]
     }
   ],
diff --git a/tests/SpecTests/retryable-writes/bulkWrite-serverErrors.json b/tests/SpecTests/retryable-writes/bulkWrite-serverErrors.json
index d9561d568..9d792ceaf 100644
--- a/tests/SpecTests/retryable-writes/bulkWrite-serverErrors.json
+++ b/tests/SpecTests/retryable-writes/bulkWrite-serverErrors.json
@@ -9,7 +9,8 @@
     {
       "minServerVersion": "4.1.7",
       "topology": [
-        "sharded"
+        "sharded",
+        "load-balanced"
       ]
     }
   ],
diff --git a/tests/SpecTests/retryable-writes/deleteMany.json b/tests/SpecTests/retryable-writes/deleteMany.json
index 642ad11fb..faa21c44f 100644
--- a/tests/SpecTests/retryable-writes/deleteMany.json
+++ b/tests/SpecTests/retryable-writes/deleteMany.json
@@ -4,7 +4,8 @@
       "minServerVersion": "3.6",
       "topology": [
         "replicaset",
-        "sharded"
+        "sharded",
+        "load-balanced"
       ]
     }
   ],
diff --git a/tests/SpecTests/retryable-writes/deleteOne-errorLabels.json b/tests/SpecTests/retryable-writes/deleteOne-errorLabels.json
index bff02e1f9..c14692fd1 100644
--- a/tests/SpecTests/retryable-writes/deleteOne-errorLabels.json
+++ b/tests/SpecTests/retryable-writes/deleteOne-errorLabels.json
@@ -4,7 +4,8 @@
       "minServerVersion": "4.3.1",
       "topology": [
         "replicaset",
-        "sharded"
+        "sharded",
+        "load-balanced"
       ]
     }
   ],
diff --git a/tests/SpecTests/retryable-writes/deleteOne-serverErrors.json b/tests/SpecTests/retryable-writes/deleteOne-serverErrors.json
index 69d225759..4eab2fa29 100644
--- a/tests/SpecTests/retryable-writes/deleteOne-serverErrors.json
+++ b/tests/SpecTests/retryable-writes/deleteOne-serverErrors.json
@@ -9,7 +9,8 @@
     {
       "minServerVersion": "4.1.7",
       "topology": [
-        "sharded"
+        "sharded",
+        "load-balanced"
       ]
     }
   ],
diff --git a/tests/SpecTests/retryable-writes/findOneAndDelete-errorLabels.json b/tests/SpecTests/retryable-writes/findOneAndDelete-errorLabels.json
index efa62dba2..60e6e0a7b 100644
--- a/tests/SpecTests/retryable-writes/findOneAndDelete-errorLabels.json
+++ b/tests/SpecTests/retryable-writes/findOneAndDelete-errorLabels.json
@@ -4,7 +4,8 @@
       "minServerVersion": "4.3.1",
       "topology": [
         "replicaset",
-        "sharded"
+        "sharded",
+        "load-balanced"
       ]
     }
   ],
diff --git a/tests/SpecTests/retryable-writes/findOneAndDelete-serverErrors.json b/tests/SpecTests/retryable-writes/findOneAndDelete-serverErrors.json
index 0785e5d03..4c1086161 100644
--- a/tests/SpecTests/retryable-writes/findOneAndDelete-serverErrors.json
+++ b/tests/SpecTests/retryable-writes/findOneAndDelete-serverErrors.json
@@ -9,7 +9,8 @@
     {
       "minServerVersion": "4.1.7",
       "topology": [
-        "sharded"
+        "sharded",
+        "load-balanced"
       ]
     }
   ],
diff --git a/tests/SpecTests/retryable-writes/findOneAndReplace-errorLabels.json b/tests/SpecTests/retryable-writes/findOneAndReplace-errorLabels.json
index d9473d139..afa2f47af 100644
--- a/tests/SpecTests/retryable-writes/findOneAndReplace-errorLabels.json
+++ b/tests/SpecTests/retryable-writes/findOneAndReplace-errorLabels.json
@@ -4,7 +4,8 @@
       "minServerVersion": "4.3.1",
       "topology": [
         "replicaset",
-        "sharded"
+        "sharded",
+        "load-balanced"
       ]
     }
   ],
diff --git a/tests/SpecTests/retryable-writes/findOneAndReplace-serverErrors.json b/tests/SpecTests/retryable-writes/findOneAndReplace-serverErrors.json
index 6ebe057cf..64c69e2f6 100644
--- a/tests/SpecTests/retryable-writes/findOneAndReplace-serverErrors.json
+++ b/tests/SpecTests/retryable-writes/findOneAndReplace-serverErrors.json
@@ -9,7 +9,8 @@
     {
       "minServerVersion": "4.1.7",
       "topology": [
-        "sharded"
+        "sharded",
+        "load-balanced"
       ]
     }
   ],
diff --git a/tests/SpecTests/retryable-writes/findOneAndUpdate-errorLabels.json b/tests/SpecTests/retryable-writes/findOneAndUpdate-errorLabels.json
index 1926d7fa5..19b3a9e77 100644
--- a/tests/SpecTests/retryable-writes/findOneAndUpdate-errorLabels.json
+++ b/tests/SpecTests/retryable-writes/findOneAndUpdate-errorLabels.json
@@ -4,7 +4,8 @@
       "minServerVersion": "4.3.1",
       "topology": [
         "replicaset",
-        "sharded"
+        "sharded",
+        "load-balanced"
       ]
     }
   ],
diff --git a/tests/SpecTests/retryable-writes/findOneAndUpdate-serverErrors.json b/tests/SpecTests/retryable-writes/findOneAndUpdate-serverErrors.json
index e6e369c13..9f5460499 100644
--- a/tests/SpecTests/retryable-writes/findOneAndUpdate-serverErrors.json
+++ b/tests/SpecTests/retryable-writes/findOneAndUpdate-serverErrors.json
@@ -9,7 +9,8 @@
     {
       "minServerVersion": "4.1.7",
       "topology": [
-        "sharded"
+        "sharded",
+        "load-balanced"
       ]
     }
   ],
diff --git a/tests/SpecTests/retryable-writes/insertMany-errorLabels.json b/tests/SpecTests/retryable-writes/insertMany-errorLabels.json
index c78946e90..65fd377fa 100644
--- a/tests/SpecTests/retryable-writes/insertMany-errorLabels.json
+++ b/tests/SpecTests/retryable-writes/insertMany-errorLabels.json
@@ -4,7 +4,8 @@
       "minServerVersion": "4.3.1",
       "topology": [
         "replicaset",
-        "sharded"
+        "sharded",
+        "load-balanced"
       ]
     }
   ],
diff --git a/tests/SpecTests/retryable-writes/insertMany-serverErrors.json b/tests/SpecTests/retryable-writes/insertMany-serverErrors.json
index 1c6ebafc2..7b45b506c 100644
--- a/tests/SpecTests/retryable-writes/insertMany-serverErrors.json
+++ b/tests/SpecTests/retryable-writes/insertMany-serverErrors.json
@@ -9,7 +9,8 @@
     {
       "minServerVersion": "4.1.7",
       "topology": [
-        "sharded"
+        "sharded",
+        "load-balanced"
       ]
     }
   ],
diff --git a/tests/SpecTests/retryable-writes/insertOne-errorLabels.json b/tests/SpecTests/retryable-writes/insertOne-errorLabels.json
index 9b8d13d52..d90ac5dfb 100644
--- a/tests/SpecTests/retryable-writes/insertOne-errorLabels.json
+++ b/tests/SpecTests/retryable-writes/insertOne-errorLabels.json
@@ -4,7 +4,8 @@
       "minServerVersion": "4.3.1",
       "topology": [
         "replicaset",
-        "sharded"
+        "sharded",
+        "load-balanced"
       ]
     }
   ],
diff --git a/tests/SpecTests/retryable-writes/insertOne-serverErrors.json b/tests/SpecTests/retryable-writes/insertOne-serverErrors.json
index fda82dabb..e8571f8cf 100644
--- a/tests/SpecTests/retryable-writes/insertOne-serverErrors.json
+++ b/tests/SpecTests/retryable-writes/insertOne-serverErrors.json
@@ -9,7 +9,8 @@
     {
       "minServerVersion": "4.1.7",
       "topology": [
-        "sharded"
+        "sharded",
+        "load-balanced"
       ]
     }
   ],
diff --git a/tests/SpecTests/retryable-writes/replaceOne-errorLabels.json b/tests/SpecTests/retryable-writes/replaceOne-errorLabels.json
index 06867e515..6029b875d 100644
--- a/tests/SpecTests/retryable-writes/replaceOne-errorLabels.json
+++ b/tests/SpecTests/retryable-writes/replaceOne-errorLabels.json
@@ -4,7 +4,8 @@
       "minServerVersion": "4.3.1",
       "topology": [
         "replicaset",
-        "sharded"
+        "sharded",
+        "load-balanced"
       ]
     }
   ],
diff --git a/tests/SpecTests/retryable-writes/replaceOne-serverErrors.json b/tests/SpecTests/retryable-writes/replaceOne-serverErrors.json
index af18bcf1a..7457228cd 100644
--- a/tests/SpecTests/retryable-writes/replaceOne-serverErrors.json
+++ b/tests/SpecTests/retryable-writes/replaceOne-serverErrors.json
@@ -9,7 +9,8 @@
     {
       "minServerVersion": "4.1.7",
       "topology": [
-        "sharded"
+        "sharded",
+        "load-balanced"
       ]
     }
   ],
diff --git a/tests/SpecTests/retryable-writes/updateMany.json b/tests/SpecTests/retryable-writes/updateMany.json
index 14288c286..46fef73e7 100644
--- a/tests/SpecTests/retryable-writes/updateMany.json
+++ b/tests/SpecTests/retryable-writes/updateMany.json
@@ -4,7 +4,8 @@
       "minServerVersion": "3.6",
       "topology": [
         "replicaset",
-        "sharded"
+        "sharded",
+        "load-balanced"
       ]
     }
   ],
diff --git a/tests/SpecTests/retryable-writes/updateOne-errorLabels.json b/tests/SpecTests/retryable-writes/updateOne-errorLabels.json
index 4a6be3ffb..5bd00cde9 100644
--- a/tests/SpecTests/retryable-writes/updateOne-errorLabels.json
+++ b/tests/SpecTests/retryable-writes/updateOne-errorLabels.json
@@ -4,7 +4,8 @@
       "minServerVersion": "4.3.1",
       "topology": [
         "replicaset",
-        "sharded"
+        "sharded",
+        "load-balanced"
       ]
     }
   ],
diff --git a/tests/SpecTests/retryable-writes/updateOne-serverErrors.json b/tests/SpecTests/retryable-writes/updateOne-serverErrors.json
index bb442eb68..116019801 100644
--- a/tests/SpecTests/retryable-writes/updateOne-serverErrors.json
+++ b/tests/SpecTests/retryable-writes/updateOne-serverErrors.json
@@ -9,7 +9,8 @@
     {
       "minServerVersion": "4.1.7",
       "topology": [
-        "sharded"
+        "sharded",
+        "load-balanced"
       ]
     }
   ],
diff --git a/tests/SpecTests/transactions/error-labels.json b/tests/SpecTests/transactions/error-labels.json
index c008a7c08..a57f216b9 100644
--- a/tests/SpecTests/transactions/error-labels.json
+++ b/tests/SpecTests/transactions/error-labels.json
@@ -10,7 +10,8 @@
       "minServerVersion": "4.1.8",
       "topology": [
         "sharded"
-      ]
+      ],
+      "serverless": "forbid"
     }
   ],
   "database_name": "transaction-tests",
diff --git a/tests/SpecTests/transactions/mongos-pin-auto.json b/tests/SpecTests/transactions/mongos-pin-auto.json
index f6ede5268..037f212f4 100644
--- a/tests/SpecTests/transactions/mongos-pin-auto.json
+++ b/tests/SpecTests/transactions/mongos-pin-auto.json
@@ -4,7 +4,8 @@
       "minServerVersion": "4.1.8",
       "topology": [
         "sharded"
-      ]
+      ],
+      "serverless": "forbid"
     }
   ],
   "database_name": "transaction-tests",
diff --git a/tests/SpecTests/transactions/mongos-recovery-token.json b/tests/SpecTests/transactions/mongos-recovery-token.json
index cd0a3c7cd..02c2002f7 100644
--- a/tests/SpecTests/transactions/mongos-recovery-token.json
+++ b/tests/SpecTests/transactions/mongos-recovery-token.json
@@ -4,7 +4,8 @@
       "minServerVersion": "4.1.8",
       "topology": [
         "sharded"
-      ]
+      ],
+      "serverless": "forbid"
     }
   ],
   "database_name": "transaction-tests",
diff --git a/tests/SpecTests/transactions/pin-mongos.json b/tests/SpecTests/transactions/pin-mongos.json
index e0f3a880b..485a3d932 100644
--- a/tests/SpecTests/transactions/pin-mongos.json
+++ b/tests/SpecTests/transactions/pin-mongos.json
@@ -4,7 +4,8 @@
       "minServerVersion": "4.1.8",
       "topology": [
         "sharded"
-      ]
+      ],
+      "serverless": "forbid"
     }
   ],
   "database_name": "transaction-tests",
diff --git a/tests/UnifiedSpecTests/UnifiedSpecTest.php b/tests/UnifiedSpecTests/UnifiedSpecTest.php
index ad9d54071..e35ff631a 100644
--- a/tests/UnifiedSpecTests/UnifiedSpecTest.php
+++ b/tests/UnifiedSpecTests/UnifiedSpecTest.php
@@ -90,6 +90,7 @@ public function provideCommandMonitoringTests()
 
     /**
      * @dataProvider provideCrudTests
+     * @group serverless
      */
     public function testCrud(UnifiedTestCase $test): void
     {
@@ -129,6 +130,7 @@ public function provideSessionsTests()
 
     /**
      * @dataProvider provideTransactionsTests
+     * @group serverless
      */
     public function testTransactions(UnifiedTestCase $test): void
     {
@@ -143,6 +145,7 @@ public function provideTransactionsTests()
     /**
      * @dataProvider provideVersionedApiTests
      * @group versioned-api
+     * @group serverless
      */
     public function testVersionedApi(UnifiedTestCase $test): void
     {
diff --git a/tests/UnifiedSpecTests/UnifiedTestRunner.php b/tests/UnifiedSpecTests/UnifiedTestRunner.php
index e39246958..aee149d30 100644
--- a/tests/UnifiedSpecTests/UnifiedTestRunner.php
+++ b/tests/UnifiedSpecTests/UnifiedTestRunner.php
@@ -19,7 +19,9 @@
 
 use function call_user_func;
 use function count;
+use function filter_var;
 use function gc_collect_cycles;
+use function getenv;
 use function in_array;
 use function is_string;
 use function PHPUnit\Framework\assertContainsOnly;
@@ -33,6 +35,8 @@
 use function strpos;
 use function version_compare;
 
+use const FILTER_VALIDATE_BOOLEAN;
+
 /**
  * Unified test runner.
  *
@@ -74,7 +78,7 @@ public function __construct(string $internalClientUri)
         /* Atlas prohibits killAllSessions. Inspect the connection string to
          * determine if we should avoid calling killAllSessions(). This does
          * mean that lingering transactions could block test execution. */
-        if (strpos($internalClientUri, self::ATLAS_TLD) !== false) {
+        if ($this->isServerless() || strpos($internalClientUri, self::ATLAS_TLD) !== false) {
             $this->allowKillAllSessions = false;
         }
     }
@@ -339,8 +343,9 @@ private function isAuthenticated(): bool
      */
     private function isServerless(): bool
     {
-        // TODO: detect serverless once PHPC-1755 is implemented
-        return false;
+        $isServerless = getenv('MONGODB_IS_SERVERLESS');
+
+        return $isServerless !== false ? filter_var($isServerless, FILTER_VALIDATE_BOOLEAN) : false;
     }
 
     /**
diff --git a/tests/UnifiedSpecTests/crud/aggregate-let.json b/tests/UnifiedSpecTests/crud/aggregate-let.json
index 4ce8256cb..d3b76bd65 100644
--- a/tests/UnifiedSpecTests/crud/aggregate-let.json
+++ b/tests/UnifiedSpecTests/crud/aggregate-let.json
@@ -1,6 +1,6 @@
 {
   "description": "aggregate-let",
-  "schemaVersion": "1.0",
+  "schemaVersion": "1.4",
   "createEntities": [
     {
       "client": {
@@ -310,7 +310,8 @@
       "description": "Aggregate to collection with let option",
       "runOnRequirements": [
         {
-          "minServerVersion": "5.0"
+          "minServerVersion": "5.0",
+          "serverless": "forbid"
         }
       ],
       "operations": [
diff --git a/tests/UnifiedSpecTests/crud/aggregate-out-readConcern.json b/tests/UnifiedSpecTests/crud/aggregate-out-readConcern.json
index 9f0a9688e..e293457c1 100644
--- a/tests/UnifiedSpecTests/crud/aggregate-out-readConcern.json
+++ b/tests/UnifiedSpecTests/crud/aggregate-out-readConcern.json
@@ -1,13 +1,14 @@
 {
   "description": "aggregate-out-readConcern",
-  "schemaVersion": "1.0",
+  "schemaVersion": "1.4",
   "runOnRequirements": [
     {
       "minServerVersion": "4.1.0",
       "topologies": [
         "replicaset",
         "sharded"
-      ]
+      ],
+      "serverless": "forbid"
     }
   ],
   "createEntities": [