diff --git a/java-spanner/google-cloud-spanner/src/main/java/com/google/cloud/spanner/SpannerImpl.java b/java-spanner/google-cloud-spanner/src/main/java/com/google/cloud/spanner/SpannerImpl.java
index c201924dfbe7..868652fdba4b 100644
--- a/java-spanner/google-cloud-spanner/src/main/java/com/google/cloud/spanner/SpannerImpl.java
+++ b/java-spanner/google-cloud-spanner/src/main/java/com/google/cloud/spanner/SpannerImpl.java
@@ -306,6 +306,17 @@ public DatabaseClient getDatabaseClient(DatabaseId db) {
       if (dbClients.containsKey(db)) {
         return dbClients.get(db);
       } else {
+        SpannerOptions opts = getOptions();
+        String metricsProject = opts.resolveMetricsProjectId();
+        if (opts.isEnableBuiltInMetrics()
+            && metricsProject != null
+            && !metricsProject.equals(db.getInstanceId().getProject())) {
+          logger.log(
+              Level.INFO,
+              "Built-in metrics project ''{0}'' differs from DatabaseId project ''{1}''."
+                  + " Use setMetricsProjectId() to override if needed.",
+              new Object[] {metricsProject, db.getInstanceId().getProject()});
+        }
         if (clientId == null) {
           clientId = nextDatabaseClientId(db);
         }
diff --git a/java-spanner/google-cloud-spanner/src/main/java/com/google/cloud/spanner/SpannerOptions.java b/java-spanner/google-cloud-spanner/src/main/java/com/google/cloud/spanner/SpannerOptions.java
index 9c542bc52365..277402eb69e0 100644
--- a/java-spanner/google-cloud-spanner/src/main/java/com/google/cloud/spanner/SpannerOptions.java
+++ b/java-spanner/google-cloud-spanner/src/main/java/com/google/cloud/spanner/SpannerOptions.java
@@ -306,6 +306,7 @@ static GcpChannelPoolOptions mergeWithDefaultChannelPoolOptions(
   private final boolean enableExtendedTracing;
   private final boolean enableEndToEndTracing;
   private final String monitoringHost;
+  private final String metricsProjectId;
   private final TransactionOptions defaultTransactionOptions;
   private final RequestOptions.ClientContext clientContext;
 
@@ -991,6 +992,7 @@ protected SpannerOptions(Builder builder) {
     }
     enableEndToEndTracing = builder.enableEndToEndTracing;
     monitoringHost = builder.monitoringHost;
+    metricsProjectId = builder.metricsProjectId;
     defaultTransactionOptions = builder.defaultTransactionOptions;
     clientContext = builder.clientContext;
   }
@@ -1251,6 +1253,7 @@ public static class Builder
     private boolean enableBuiltInMetrics = SpannerOptions.environment.isEnableBuiltInMetrics();
     private boolean enableLocationApi = SpannerOptions.environment.isEnableLocationApi();
     private String monitoringHost = SpannerOptions.environment.getMonitoringHost();
+    private String metricsProjectId;
     private SslContext mTLSContext = null;
     private String experimentalHost = null;
     private boolean usePlainText = false;
@@ -1360,6 +1363,7 @@ protected Builder() {
       this.enableLocationApi = options.enableLocationApi;
       this.enableEndToEndTracing = options.enableEndToEndTracing;
       this.monitoringHost = options.monitoringHost;
+      this.metricsProjectId = options.metricsProjectId;
       this.defaultTransactionOptions = options.defaultTransactionOptions;
       this.clientContext = options.clientContext;
     }
@@ -2033,6 +2037,17 @@ public Builder setMonitoringHost(String monitoringHost) {
       return this;
     }
 
+    /**
+     * Sets the GCP project ID for exporting client-side built-in metrics. Defaults to {@link
+     * SpannerOptions#getProjectId()} when not set. On GKE with shared VPC, the default project may
+     * resolve to the host project instead of the application project; set this explicitly to avoid
+     * {@code monitoring.metricWriter} permission errors.
+     */
+    public Builder setMetricsProjectId(String metricsProjectId) {
+      this.metricsProjectId = metricsProjectId;
+      return this;
+    }
+
     /**
      * Sets whether to enable extended OpenTelemetry tracing. Enabling this option will add the
      * following additional attributes to the traces that are generated by the client:
@@ -2443,14 +2458,14 @@ public ApiTracerFactory getApiTracerFactory() {
   @InternalApi
   public OpenTelemetry getBuiltInOpenTelemetry() {
     return this.builtInMetricsProvider.getOrCreateOpenTelemetry(
-        this.getProjectId(), getCredentials(), this.monitoringHost, getUniverseDomain());
+        this.resolveMetricsProjectId(), getCredentials(), this.monitoringHost, getUniverseDomain());
   }
 
   public void enablegRPCMetrics(InstantiatingGrpcChannelProvider.Builder channelProviderBuilder) {
     if (isEnableBuiltInMetrics() && SpannerOptions.environment.isEnableGRPCBuiltInMetrics()) {
       this.builtInMetricsProvider.enableGrpcMetrics(
           channelProviderBuilder,
-          this.getProjectId(),
+          this.resolveMetricsProjectId(),
           getCredentials(),
           this.monitoringHost,
           getUniverseDomain());
@@ -2499,7 +2514,7 @@ private ApiTracerFactory getDefaultApiTracerFactory() {
   private ApiTracerFactory createMetricsApiTracerFactory() {
     OpenTelemetry openTelemetry =
         this.builtInMetricsProvider.getOrCreateOpenTelemetry(
-            this.getProjectId(), getCredentials(), this.monitoringHost, getUniverseDomain());
+            this.resolveMetricsProjectId(), getCredentials(), this.monitoringHost, getUniverseDomain());
 
     return openTelemetry != null
         ? new BuiltInMetricsTracerFactory(
@@ -2543,6 +2558,19 @@ String getMonitoringHost() {
     return monitoringHost;
   }
 
+  /**
+   * Returns the GCP project ID for client-side metrics export. Returns the explicit value if set
+   * via {@link Builder#setMetricsProjectId}, otherwise falls back to {@link #getProjectId()}.
+   */
+  String resolveMetricsProjectId() {
+    return metricsProjectId != null ? metricsProjectId : getProjectId();
+  }
+
+  /** Returns the explicitly configured metrics project ID, or null if not set. */
+  public String getMetricsProjectId() {
+    return metricsProjectId;
+  }
+
   public TransactionOptions getDefaultTransactionOptions() {
     return defaultTransactionOptions;
   }