diff --git a/manifest.json b/manifest.json
index eadfb4d05..bb95605ee 100644
--- a/manifest.json
+++ b/manifest.json
@@ -1,6 +1,6 @@
 {
     "variables": {
-        "${LATEST}": "3.330.0"
+        "${LATEST}": "3.330.1"
     },
     "endpoints": "https://raw.githubusercontent.com/aws/aws-sdk-php/${LATEST}/src/data/endpoints.json",
     "services": {
diff --git a/src/Service/S3/CHANGELOG.md b/src/Service/S3/CHANGELOG.md
index 840efb24b..a91945fd5 100644
--- a/src/Service/S3/CHANGELOG.md
+++ b/src/Service/S3/CHANGELOG.md
@@ -2,6 +2,10 @@
 
 ## NOT RELEASED
 
+### Added
+
+- AWS api-change: Amazon Simple Storage Service / Features: Add support for ETag based conditional writes in PutObject and CompleteMultiPartUpload APIs to prevent unintended object modifications.
+
 ## 2.5.0
 
 ### Added
diff --git a/src/Service/S3/composer.json b/src/Service/S3/composer.json
index f08e84c7a..2da72119e 100644
--- a/src/Service/S3/composer.json
+++ b/src/Service/S3/composer.json
@@ -30,7 +30,7 @@
     },
     "extra": {
         "branch-alias": {
-            "dev-master": "2.5-dev"
+            "dev-master": "2.6-dev"
         }
     }
 }
diff --git a/src/Service/S3/src/Input/CompleteMultipartUploadRequest.php b/src/Service/S3/src/Input/CompleteMultipartUploadRequest.php
index d28ff2c56..069464355 100644
--- a/src/Service/S3/src/Input/CompleteMultipartUploadRequest.php
+++ b/src/Service/S3/src/Input/CompleteMultipartUploadRequest.php
@@ -127,6 +127,26 @@ final class CompleteMultipartUploadRequest extends Input
      */
     private $expectedBucketOwner;
 
+    /**
+     * Uploads the object only if the ETag (entity tag) value provided during the WRITE operation matches the ETag of the
+     * object in S3. If the ETag values do not match, the operation returns a `412 Precondition Failed` error.
+     *
+     * If a conflicting operation occurs during the upload S3 returns a `409 ConditionalRequestConflict` response. On a 409
+     * failure you should fetch the object's ETag, re-initiate the multipart upload with `CreateMultipartUpload`, and
+     * re-upload each part.
+     *
+     * Expects the ETag value as a string.
+     *
+     * For more information about conditional requests, see RFC 7232 [^1], or Conditional requests [^2] in the *Amazon S3
+     * User Guide*.
+     *
+     * [^1]: https://tools.ietf.org/html/rfc7232
+     * [^2]: https://docs.aws.amazon.com/AmazonS3/latest/userguide/conditional-requests.html
+     *
+     * @var string|null
+     */
+    private $ifMatch;
+
     /**
      * Uploads the object only if the object key name does not already exist in the bucket specified. Otherwise, Amazon S3
      * returns a `412 Precondition Failed` error.
@@ -197,6 +217,7 @@ final class CompleteMultipartUploadRequest extends Input
      *   ChecksumSHA256?: null|string,
      *   RequestPayer?: null|RequestPayer::*,
      *   ExpectedBucketOwner?: null|string,
+     *   IfMatch?: null|string,
      *   IfNoneMatch?: null|string,
      *   SSECustomerAlgorithm?: null|string,
      *   SSECustomerKey?: null|string,
@@ -216,6 +237,7 @@ public function __construct(array $input = [])
         $this->checksumSha256 = $input['ChecksumSHA256'] ?? null;
         $this->requestPayer = $input['RequestPayer'] ?? null;
         $this->expectedBucketOwner = $input['ExpectedBucketOwner'] ?? null;
+        $this->ifMatch = $input['IfMatch'] ?? null;
         $this->ifNoneMatch = $input['IfNoneMatch'] ?? null;
         $this->sseCustomerAlgorithm = $input['SSECustomerAlgorithm'] ?? null;
         $this->sseCustomerKey = $input['SSECustomerKey'] ?? null;
@@ -235,6 +257,7 @@ public function __construct(array $input = [])
      *   ChecksumSHA256?: null|string,
      *   RequestPayer?: null|RequestPayer::*,
      *   ExpectedBucketOwner?: null|string,
+     *   IfMatch?: null|string,
      *   IfNoneMatch?: null|string,
      *   SSECustomerAlgorithm?: null|string,
      *   SSECustomerKey?: null|string,
@@ -277,6 +300,11 @@ public function getExpectedBucketOwner(): ?string
         return $this->expectedBucketOwner;
     }
 
+    public function getIfMatch(): ?string
+    {
+        return $this->ifMatch;
+    }
+
     public function getIfNoneMatch(): ?string
     {
         return $this->ifNoneMatch;
@@ -348,6 +376,9 @@ public function request(): Request
         if (null !== $this->expectedBucketOwner) {
             $headers['x-amz-expected-bucket-owner'] = $this->expectedBucketOwner;
         }
+        if (null !== $this->ifMatch) {
+            $headers['If-Match'] = $this->ifMatch;
+        }
         if (null !== $this->ifNoneMatch) {
             $headers['If-None-Match'] = $this->ifNoneMatch;
         }
@@ -433,6 +464,13 @@ public function setExpectedBucketOwner(?string $value): self
         return $this;
     }
 
+    public function setIfMatch(?string $value): self
+    {
+        $this->ifMatch = $value;
+
+        return $this;
+    }
+
     public function setIfNoneMatch(?string $value): self
     {
         $this->ifNoneMatch = $value;
diff --git a/src/Service/S3/src/Input/PutObjectRequest.php b/src/Service/S3/src/Input/PutObjectRequest.php
index 66776918a..e9195c640 100644
--- a/src/Service/S3/src/Input/PutObjectRequest.php
+++ b/src/Service/S3/src/Input/PutObjectRequest.php
@@ -251,6 +251,25 @@ final class PutObjectRequest extends Input
      */
     private $expires;
 
+    /**
+     * Uploads the object only if the ETag (entity tag) value provided during the WRITE operation matches the ETag of the
+     * object in S3. If the ETag values do not match, the operation returns a `412 Precondition Failed` error.
+     *
+     * If a conflicting operation occurs during the upload S3 returns a `409 ConditionalRequestConflict` response. On a 409
+     * failure you should fetch the object's ETag and retry the upload.
+     *
+     * Expects the ETag value as a string.
+     *
+     * For more information about conditional requests, see RFC 7232 [^1], or Conditional requests [^2] in the *Amazon S3
+     * User Guide*.
+     *
+     * [^1]: https://tools.ietf.org/html/rfc7232
+     * [^2]: https://docs.aws.amazon.com/AmazonS3/latest/userguide/conditional-requests.html
+     *
+     * @var string|null
+     */
+    private $ifMatch;
+
     /**
      * Uploads the object only if the object key name does not already exist in the bucket specified. Otherwise, Amazon S3
      * returns a `412 Precondition Failed` error.
@@ -597,6 +616,7 @@ final class PutObjectRequest extends Input
      *   ChecksumSHA1?: null|string,
      *   ChecksumSHA256?: null|string,
      *   Expires?: null|\DateTimeImmutable|string,
+     *   IfMatch?: null|string,
      *   IfNoneMatch?: null|string,
      *   GrantFullControl?: null|string,
      *   GrantRead?: null|string,
@@ -641,6 +661,7 @@ public function __construct(array $input = [])
         $this->checksumSha1 = $input['ChecksumSHA1'] ?? null;
         $this->checksumSha256 = $input['ChecksumSHA256'] ?? null;
         $this->expires = !isset($input['Expires']) ? null : ($input['Expires'] instanceof \DateTimeImmutable ? $input['Expires'] : new \DateTimeImmutable($input['Expires']));
+        $this->ifMatch = $input['IfMatch'] ?? null;
         $this->ifNoneMatch = $input['IfNoneMatch'] ?? null;
         $this->grantFullControl = $input['GrantFullControl'] ?? null;
         $this->grantRead = $input['GrantRead'] ?? null;
@@ -685,6 +706,7 @@ public function __construct(array $input = [])
      *   ChecksumSHA1?: null|string,
      *   ChecksumSHA256?: null|string,
      *   Expires?: null|\DateTimeImmutable|string,
+     *   IfMatch?: null|string,
      *   IfNoneMatch?: null|string,
      *   GrantFullControl?: null|string,
      *   GrantRead?: null|string,
@@ -835,6 +857,11 @@ public function getGrantWriteAcp(): ?string
         return $this->grantWriteAcp;
     }
 
+    public function getIfMatch(): ?string
+    {
+        return $this->ifMatch;
+    }
+
     public function getIfNoneMatch(): ?string
     {
         return $this->ifNoneMatch;
@@ -993,6 +1020,9 @@ public function request(): Request
         if (null !== $this->expires) {
             $headers['Expires'] = $this->expires->setTimezone(new \DateTimeZone('GMT'))->format(\DateTimeInterface::RFC7231);
         }
+        if (null !== $this->ifMatch) {
+            $headers['If-Match'] = $this->ifMatch;
+        }
         if (null !== $this->ifNoneMatch) {
             $headers['If-None-Match'] = $this->ifNoneMatch;
         }
@@ -1262,6 +1292,13 @@ public function setGrantWriteAcp(?string $value): self
         return $this;
     }
 
+    public function setIfMatch(?string $value): self
+    {
+        $this->ifMatch = $value;
+
+        return $this;
+    }
+
     public function setIfNoneMatch(?string $value): self
     {
         $this->ifNoneMatch = $value;
diff --git a/src/Service/S3/src/S3Client.php b/src/Service/S3/src/S3Client.php
index d65fda8dc..ee7307e01 100644
--- a/src/Service/S3/src/S3Client.php
+++ b/src/Service/S3/src/S3Client.php
@@ -347,6 +347,7 @@ public function bucketNotExists($input): BucketNotExistsWaiter
      *   ChecksumSHA256?: null|string,
      *   RequestPayer?: null|RequestPayer::*,
      *   ExpectedBucketOwner?: null|string,
+     *   IfMatch?: null|string,
      *   IfNoneMatch?: null|string,
      *   SSECustomerAlgorithm?: null|string,
      *   SSECustomerKey?: null|string,
@@ -2467,6 +2468,7 @@ public function putBucketTagging($input): Result
      *   ChecksumSHA1?: null|string,
      *   ChecksumSHA256?: null|string,
      *   Expires?: null|\DateTimeImmutable|string,
+     *   IfMatch?: null|string,
      *   IfNoneMatch?: null|string,
      *   GrantFullControl?: null|string,
      *   GrantRead?: null|string,