diff --git a/aws/middleware/user_agent.go b/aws/middleware/user_agent.go
index 02182220cb1..01d758d5ff8 100644
--- a/aws/middleware/user_agent.go
+++ b/aws/middleware/user_agent.go
@@ -89,15 +89,15 @@ const (
 	UserAgentFeatureS3AccessGrants                                 = "K" // not yet implemented
 	UserAgentFeatureGZIPRequestCompression                         = "L"
 	UserAgentFeatureProtocolRPCV2CBOR                              = "M"
-	UserAgentFeatureRequestChecksumWhenSupported                   = "Z"
-	UserAgentFeatureRequestChecksumWhenRequired                    = "a"
-	UserAgentFeatureResponseChecksumWhenSupported                  = "b"
-	UserAgentFeatureResponseChecksumWhenRequired                   = "c"
 	UserAgentFeatureRequestChecksumCRC32                           = "U"
 	UserAgentFeatureRequestChecksumCRC32C                          = "V"
 	UserAgentFeatureRequestChecksumCRC64                           = "W"
 	UserAgentFeatureRequestChecksumSHA1                            = "X"
 	UserAgentFeatureRequestChecksumSHA256                          = "Y"
+	UserAgentFeatureRequestChecksumWhenSupported                   = "Z"
+	UserAgentFeatureRequestChecksumWhenRequired                    = "a"
+	UserAgentFeatureResponseChecksumWhenSupported                  = "b"
+	UserAgentFeatureResponseChecksumWhenRequired                   = "c"
 )
 
 // RequestUserAgent is a build middleware that set the User-Agent for the request.
diff --git a/feature/s3/manager/integ_upload_test.go b/feature/s3/manager/integ_upload_test.go
index 3a289459f93..96383c243eb 100644
--- a/feature/s3/manager/integ_upload_test.go
+++ b/feature/s3/manager/integ_upload_test.go
@@ -222,7 +222,7 @@ func TestInteg_UploadPresetChecksum(t *testing.T) {
 			},
 		},
 		"auto multipart part": {
-			"no checksum": {
+			"no checksum algorithm passed": {
 				payload: bytes.NewReader(multiPartBytes),
 				expectParts: []s3types.CompletedPart{
 					{
diff --git a/service/internal/checksum/algorithms_test.go b/service/internal/checksum/algorithms_test.go
index 7c821f1e2a5..05e46fb1050 100644
--- a/service/internal/checksum/algorithms_test.go
+++ b/service/internal/checksum/algorithms_test.go
@@ -1,5 +1,5 @@
-//go:build go1.16
-// +build go1.16
+//go:build go1.21
+// +build go1.21
 
 package checksum
 
diff --git a/service/internal/checksum/aws_chunked_encoding_test.go b/service/internal/checksum/aws_chunked_encoding_test.go
index 4f208b4c099..5b991b14b86 100644
--- a/service/internal/checksum/aws_chunked_encoding_test.go
+++ b/service/internal/checksum/aws_chunked_encoding_test.go
@@ -1,5 +1,5 @@
-//go:build go1.16
-// +build go1.16
+//go:build go1.21
+// +build go1.21
 
 package checksum
 
diff --git a/service/internal/checksum/middleware_add_test.go b/service/internal/checksum/middleware_add_test.go
index 7219c4a4172..20e8c72a483 100644
--- a/service/internal/checksum/middleware_add_test.go
+++ b/service/internal/checksum/middleware_add_test.go
@@ -1,5 +1,5 @@
-//go:build go1.16
-// +build go1.16
+//go:build go1.21
+// +build go1.21
 
 package checksum
 
diff --git a/service/internal/checksum/middleware_checksum_metrics_tracking_test.go b/service/internal/checksum/middleware_checksum_metrics_tracking_test.go
index aad42493c5b..cbbbb8d230c 100644
--- a/service/internal/checksum/middleware_checksum_metrics_tracking_test.go
+++ b/service/internal/checksum/middleware_checksum_metrics_tracking_test.go
@@ -1,5 +1,5 @@
-//go:build go1.16
-// +build go1.16
+//go:build go1.21
+// +build go1.21
 
 package checksum
 
@@ -10,56 +10,10 @@ import (
 	"github.com/aws/smithy-go/middleware"
 	smithyhttp "github.com/aws/smithy-go/transport/http"
 	"net/http"
-	"runtime"
 	"strings"
 	"testing"
 )
 
-var expectedAgent = aws.SDKName + "/" + aws.SDKVersion +
-	" ua/2.1" +
-	" os/" + getNormalizedOSName() +
-	" lang/go#" + strings.Map(rules, languageVersion) + // normalize as the user-agent builder will
-	" md/GOOS#" + runtime.GOOS +
-	" md/GOARCH#" + runtime.GOARCH
-
-var languageVersion = strings.TrimPrefix(runtime.Version(), "go")
-
-func getNormalizedOSName() (os string) {
-	switch runtime.GOOS {
-	case "android":
-		os = "android"
-	case "linux":
-		os = "linux"
-	case "windows":
-		os = "windows"
-	case "darwin":
-		os = "macos"
-	case "ios":
-		os = "ios"
-	default:
-		os = "other"
-	}
-	return os
-}
-
-var validChars = map[rune]bool{
-	'!': true, '#': true, '$': true, '%': true, '&': true, '\'': true, '*': true, '+': true,
-	'-': true, '.': true, '^': true, '_': true, '`': true, '|': true, '~': true,
-}
-
-func rules(r rune) rune {
-	switch {
-	case r >= '0' && r <= '9':
-		return r
-	case r >= 'A' && r <= 'Z' || r >= 'a' && r <= 'z':
-		return r
-	case validChars[r]:
-		return r
-	default:
-		return '-'
-	}
-}
-
 func TestRequestChecksumMetricsTracking(t *testing.T) {
 	cases := map[string]struct {
 		requestChecksumCalculation aws.RequestChecksumCalculation
@@ -69,26 +23,26 @@ func TestRequestChecksumMetricsTracking(t *testing.T) {
 		"default": {
 			requestChecksumCalculation: aws.RequestChecksumCalculationWhenSupported,
 			reqHeaders:                 map[string][]string{},
-			expectedUserAgentHeader:    expectedAgent + " m/Z",
+			expectedUserAgentHeader:    " m/Z",
 		},
 		"calculate checksum when required": {
 			requestChecksumCalculation: aws.RequestChecksumCalculationWhenRequired,
 			reqHeaders:                 map[string][]string{},
-			expectedUserAgentHeader:    expectedAgent + " m/a",
+			expectedUserAgentHeader:    " m/a",
 		},
 		"default with crc32 checksum": {
 			requestChecksumCalculation: aws.RequestChecksumCalculationWhenSupported,
 			reqHeaders: map[string][]string{
 				"X-Amz-Checksum-Crc32": {"aa"},
 			},
-			expectedUserAgentHeader: expectedAgent + " m/U,Z",
+			expectedUserAgentHeader: " m/U,Z",
 		},
 		"calculate checksum when required with sha256 checksum": {
 			requestChecksumCalculation: aws.RequestChecksumCalculationWhenRequired,
 			reqHeaders: map[string][]string{
 				"X-Amz-Checksum-Sha256": {"aa"},
 			},
-			expectedUserAgentHeader: expectedAgent + " m/Y,a",
+			expectedUserAgentHeader: " m/Y,a",
 		},
 		"default with crc32c and crc64": {
 			requestChecksumCalculation: aws.RequestChecksumCalculationWhenSupported,
@@ -96,7 +50,7 @@ func TestRequestChecksumMetricsTracking(t *testing.T) {
 				"X-Amz-Checksum-Crc32c":    {"aa"},
 				"X-Amz-Checksum-Crc64nvme": {"aa"},
 			},
-			expectedUserAgentHeader: expectedAgent + " m/V,W,Z",
+			expectedUserAgentHeader: " m/V,W,Z",
 		},
 	}
 
@@ -120,8 +74,8 @@ func TestRequestChecksumMetricsTracking(t *testing.T) {
 					return
 				}))
 
-			if e, a := c.expectedUserAgentHeader, req.Header["User-Agent"][0]; e != a {
-				t.Errorf("expected user agent header to be %s, got %s", e, a)
+			if e, a := c.expectedUserAgentHeader, req.Header["User-Agent"][0]; !strings.Contains(a, e) {
+				t.Errorf("expected user agent header to include %s, got %s", e, a)
 			}
 		})
 	}
@@ -134,11 +88,11 @@ func TestResponseChecksumMetricsTracking(t *testing.T) {
 	}{
 		"default": {
 			responseChecksumValidation: aws.ResponseChecksumValidationWhenSupported,
-			expectedUserAgentHeader:    expectedAgent + " m/b",
+			expectedUserAgentHeader:    " m/b",
 		},
 		"validate checksum when required": {
 			responseChecksumValidation: aws.ResponseChecksumValidationWhenRequired,
-			expectedUserAgentHeader:    expectedAgent + " m/c",
+			expectedUserAgentHeader:    " m/c",
 		},
 	}
 
@@ -161,8 +115,8 @@ func TestResponseChecksumMetricsTracking(t *testing.T) {
 					return
 				}))
 
-			if e, a := c.expectedUserAgentHeader, req.Header["User-Agent"][0]; e != a {
-				t.Errorf("expected user agent header to be %s, got %s", e, a)
+			if e, a := c.expectedUserAgentHeader, req.Header["User-Agent"][0]; !strings.Contains(a, e) {
+				t.Errorf("expected user agent header to contain %s, got %s", e, a)
 			}
 		})
 	}
diff --git a/service/internal/checksum/middleware_compute_input_checksum_test.go b/service/internal/checksum/middleware_compute_input_checksum_test.go
index 43dc87a7ef0..a2e9b02df83 100644
--- a/service/internal/checksum/middleware_compute_input_checksum_test.go
+++ b/service/internal/checksum/middleware_compute_input_checksum_test.go
@@ -1,5 +1,5 @@
-//go:build go1.16
-// +build go1.16
+//go:build go1.21
+// +build go1.21
 
 package checksum
 
diff --git a/service/internal/checksum/middleware_setup_context_test.go b/service/internal/checksum/middleware_setup_context_test.go
index 0f766430eb8..81c7250940a 100644
--- a/service/internal/checksum/middleware_setup_context_test.go
+++ b/service/internal/checksum/middleware_setup_context_test.go
@@ -1,5 +1,5 @@
-//go:build go1.16
-// +build go1.16
+//go:build go1.21
+// +build go1.21
 
 package checksum
 
diff --git a/service/internal/checksum/middleware_validate_output_test.go b/service/internal/checksum/middleware_validate_output_test.go
index 618c233dc6f..2b2d4bbca6d 100644
--- a/service/internal/checksum/middleware_validate_output_test.go
+++ b/service/internal/checksum/middleware_validate_output_test.go
@@ -1,5 +1,5 @@
-//go:build go1.16
-// +build go1.16
+//go:build go1.21
+// +build go1.21
 
 package checksum