diff --git a/.github/resources/integ-service-account.json.gpg b/.github/resources/integ-service-account.json.gpg
index 145389e0..7740dccd 100644
Binary files a/.github/resources/integ-service-account.json.gpg and b/.github/resources/integ-service-account.json.gpg differ
diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 42991681..43c8cdc2 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -8,7 +8,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        go: ['1.20', '1.21', '1.22']
+        go: ['1.21', '1.22', '1.23']
 
     steps:
     - name: Check out code
diff --git a/.github/workflows/nightly.yml b/.github/workflows/nightly.yml
index 6e89ee5a..fbee4368 100644
--- a/.github/workflows/nightly.yml
+++ b/.github/workflows/nightly.yml
@@ -36,7 +36,7 @@ jobs:
     - name: Set up Go
       uses: actions/setup-go@v5
       with:
-        go-version: '1.20'
+        go-version: '1.21'
 
     - name: Install golint
       run: go install golang.org/x/lint/golint@latest
diff --git a/.github/workflows/release.yml b/.github/workflows/release.yml
index 5026fd0c..a164bdca 100644
--- a/.github/workflows/release.yml
+++ b/.github/workflows/release.yml
@@ -47,7 +47,7 @@ jobs:
     - name: Set up Go
       uses: actions/setup-go@v5
       with:
-        go-version: '1.20'
+        go-version: '1.21'
 
     - name: Install golint
       run: go install golang.org/x/lint/golint@latest
diff --git a/README.md b/README.md
index 6a042cc5..34a1e610 100644
--- a/README.md
+++ b/README.md
@@ -45,9 +45,9 @@ requests, code review feedback, and also pull requests.
 ## Supported Go Versions
 
 The Admin Go SDK is compatible with at least the three most recent, major Go releases.
-We currently support Go v1.20 and higher.
+We currently support Go v1.21 and higher.
 [Continuous integration](https://github.com/firebase/firebase-admin-go/actions) system
-tests the code on Go v1.20 through v1.22.
+tests the code on Go v1.21 through v1.23.
 
 ## Documentation
 
diff --git a/auth/auth.go b/auth/auth.go
index d6299611..0bda04a0 100644
--- a/auth/auth.go
+++ b/auth/auth.go
@@ -21,6 +21,7 @@ import (
 	"errors"
 	"fmt"
 	"os"
+	"runtime"
 	"strings"
 	"time"
 
@@ -133,10 +134,12 @@ func NewClient(ctx context.Context, conf *internal.AuthConfig) (*Client, error)
 		return nil, err
 	}
 
+	goVersion := strings.TrimPrefix(runtime.Version(), "go")
 	hc := internal.WithDefaultRetryConfig(transport)
 	hc.CreateErrFn = handleHTTPError
 	hc.Opts = []internal.HTTPOption{
 		internal.WithHeader("X-Client-Version", fmt.Sprintf("Go/Admin/%s", conf.Version)),
+		internal.WithHeader("x-goog-api-client", fmt.Sprintf("gl-go/%s fire-admin/%s", goVersion, conf.Version)),
 	}
 
 	baseURL := defaultAuthURL
diff --git a/auth/auth_test.go b/auth/auth_test.go
index 30fbde88..2a00220b 100644
--- a/auth/auth_test.go
+++ b/auth/auth_test.go
@@ -23,6 +23,7 @@ import (
 	"log"
 	"net/http"
 	"os"
+	"runtime"
 	"strings"
 	"syscall"
 	"testing"
@@ -1451,6 +1452,13 @@ func checkBaseClient(client *Client, wantProjectID string) error {
 		return fmt.Errorf("version = %q; want = %q", version, wantVersion)
 	}
 
+	goVersion := strings.TrimPrefix(runtime.Version(), "go")
+	xGoogAPIClientHeader := req.Header.Get("x-goog-api-client")
+	wantXGoogAPIClientHeader := fmt.Sprintf("gl-go/%s fire-admin/%s", goVersion, testVersion)
+	if xGoogAPIClientHeader != wantXGoogAPIClientHeader {
+		return fmt.Errorf("x-goog-api-client header = %q; want = %q", xGoogAPIClientHeader, wantXGoogAPIClientHeader)
+	}
+
 	return nil
 }
 
diff --git a/auth/user_mgt_test.go b/auth/user_mgt_test.go
index ffa48655..902ed280 100644
--- a/auth/user_mgt_test.go
+++ b/auth/user_mgt_test.go
@@ -24,6 +24,7 @@ import (
 	"net/http"
 	"net/http/httptest"
 	"reflect"
+	"runtime"
 	"sort"
 	"strconv"
 	"strings"
@@ -2315,6 +2316,12 @@ func echoServer(resp interface{}, t *testing.T) *mockAuthServer {
 			t.Errorf("X-Client-Version header = %q; want: %q", gh, wh)
 		}
 
+		gh = r.Header.Get("x-goog-api-client")
+		wh = fmt.Sprintf("gl-go/%s fire-admin/%s", strings.TrimPrefix(runtime.Version(), "go"), testVersion)
+		if gh != wh {
+			t.Errorf("x-goog-api-client header = %q; want: %q", gh, wh)
+		}
+
 		for k, v := range s.Header {
 			w.Header().Set(k, v)
 		}
diff --git a/firebase.go b/firebase.go
index 47a1006e..8b1facd4 100644
--- a/firebase.go
+++ b/firebase.go
@@ -39,7 +39,7 @@ import (
 var defaultAuthOverrides = make(map[string]interface{})
 
 // Version of the Firebase Go Admin SDK.
-const Version = "4.14.1"
+const Version = "4.15.0"
 
 // firebaseEnvName is the name of the environment variable with the Config.
 const firebaseEnvName = "FIREBASE_CONFIG"
diff --git a/go.mod b/go.mod
index 945b981e..b9a1c22c 100644
--- a/go.mod
+++ b/go.mod
@@ -1,6 +1,6 @@
 module firebase.google.com/go/v4
 
-go 1.20
+go 1.21
 
 require (
 	cloud.google.com/go/firestore v1.15.0
diff --git a/integration/messaging/messaging_test.go b/integration/messaging/messaging_test.go
index 85b475ae..e32aac9d 100644
--- a/integration/messaging/messaging_test.go
+++ b/integration/messaging/messaging_test.go
@@ -230,6 +230,7 @@ func TestSendEachForMulticast(t *testing.T) {
 }
 
 func TestSendAll(t *testing.T) {
+	t.Skip("Skipping integration tests for deprecated sendAll() API")
 	messages := []*messaging.Message{
 		{
 			Notification: &messaging.Notification{
@@ -289,6 +290,7 @@ func TestSendAll(t *testing.T) {
 }
 
 func TestSendFiveHundred(t *testing.T) {
+	t.Skip("Skipping integration tests for deprecated sendAll() API")
 	var messages []*messaging.Message
 	const limit = 500
 	for i := 0; i < limit; i++ {
@@ -322,6 +324,7 @@ func TestSendFiveHundred(t *testing.T) {
 }
 
 func TestSendMulticast(t *testing.T) {
+	t.Skip("Skipping integration tests for deprecated SendMulticast() API")
 	message := &messaging.MulticastMessage{
 		Notification: &messaging.Notification{
 			Title: "title",
diff --git a/messaging/messaging.go b/messaging/messaging.go
index 858e75ff..525cccb6 100644
--- a/messaging/messaging.go
+++ b/messaging/messaging.go
@@ -23,6 +23,7 @@ import (
 	"fmt"
 	"net/http"
 	"regexp"
+	"runtime"
 	"strconv"
 	"strings"
 	"time"
@@ -121,6 +122,7 @@ type AndroidConfig struct {
 	Data                  map[string]string    `json:"data,omitempty"` // if specified, overrides the Data field on Message type
 	Notification          *AndroidNotification `json:"notification,omitempty"`
 	FCMOptions            *AndroidFCMOptions   `json:"fcm_options,omitempty"`
+	DirectBootOK          bool                 `json:"direct_boot_ok,omitempty"`
 }
 
 // MarshalJSON marshals an AndroidConfig into JSON (for internal use only).
@@ -892,10 +894,12 @@ func newFCMClient(hc *http.Client, conf *internal.MessagingConfig, messagingEndp
 	client := internal.WithDefaultRetryConfig(hc)
 	client.CreateErrFn = handleFCMError
 
+	goVersion := strings.TrimPrefix(runtime.Version(), "go")
 	version := fmt.Sprintf("fire-admin-go/%s", conf.Version)
 	client.Opts = []internal.HTTPOption{
 		internal.WithHeader(apiFormatVersionHeader, apiFormatVersion),
 		internal.WithHeader(firebaseClientHeader, version),
+		internal.WithHeader("x-goog-api-client", fmt.Sprintf("gl-go/%s fire-admin/%s", goVersion, conf.Version)),
 	}
 
 	return &fcmClient{
diff --git a/messaging/messaging_test.go b/messaging/messaging_test.go
index 388154b0..8b31fc46 100644
--- a/messaging/messaging_test.go
+++ b/messaging/messaging_test.go
@@ -21,6 +21,8 @@ import (
 	"net/http"
 	"net/http/httptest"
 	"reflect"
+	"runtime"
+	"strings"
 	"testing"
 	"time"
 
@@ -144,6 +146,35 @@ var validMessages = []struct {
 			"topic": "test-topic",
 		},
 	},
+	{
+		name: "AndroidDataMessage",
+		req: &Message{
+			Android: &AndroidConfig{
+				DirectBootOK: true,
+				CollapseKey:  "ck",
+				Data: map[string]string{
+					"k1": "v1",
+					"k2": "v2",
+				},
+				Priority: "normal",
+				TTL:      &ttl,
+			},
+			Topic: "test-topic",
+		},
+		want: map[string]interface{}{
+			"android": map[string]interface{}{
+				"direct_boot_ok": true,
+				"collapse_key":   "ck",
+				"data": map[string]interface{}{
+					"k1": "v1",
+					"k2": "v2",
+				},
+				"priority": "normal",
+				"ttl":      "10s",
+			},
+			"topic": "test-topic",
+		},
+	},
 	{
 		name: "AndroidNotificationMessage",
 		req: &Message{
@@ -1365,6 +1396,11 @@ func checkFCMRequest(t *testing.T, b []byte, tr *http.Request, want map[string]i
 	if h := tr.Header.Get("X-FIREBASE-CLIENT"); h != clientVersion {
 		t.Errorf("X-FIREBASE-CLIENT = %q; want = %q", h, clientVersion)
 	}
+	goVersion := strings.TrimPrefix(runtime.Version(), "go")
+	xGoogAPIClientHeader := "gl-go/" + goVersion + " fire-admin/" + testMessagingConfig.Version
+	if h := tr.Header.Get("x-goog-api-client"); h != xGoogAPIClientHeader {
+		t.Errorf("x-goog-api-client header = %q; want = %q", h, xGoogAPIClientHeader)
+	}
 }
 
 var httpErrors = []struct {