diff --git a/src/Elastic.Transport/Products/DefaultProductRegistration.cs b/src/Elastic.Transport/Products/DefaultProductRegistration.cs
index 2c4e033..542a595 100644
--- a/src/Elastic.Transport/Products/DefaultProductRegistration.cs
+++ b/src/Elastic.Transport/Products/DefaultProductRegistration.cs
@@ -22,7 +22,7 @@ public sealed class DefaultProductRegistration : ProductRegistration
 	/// <summary>
 	/// 
 	/// </summary>
-	public DefaultProductRegistration() => _metaHeaderProvider = new DefaultMetaHeaderProvider(typeof(HttpTransport), "et");
+	public DefaultProductRegistration() => _metaHeaderProvider = new DefaultMetaHeaderProvider(typeof(HttpTransport), ServiceIdentifier);
 
 	/// <summary> A static instance of <see cref="DefaultProductRegistration"/> to promote reuse </summary>
 	public static DefaultProductRegistration Default { get; } = new DefaultProductRegistration();
@@ -30,6 +30,9 @@ public sealed class DefaultProductRegistration : ProductRegistration
 	/// <inheritdoc cref="ProductRegistration.Name"/>
 	public override string Name { get; } = "elastic-transport-net";
 
+	/// <inheritdoc cref="ProductRegistration.ServiceIdentifier"/>
+	public override string? ServiceIdentifier => "et";
+
 	/// <inheritdoc cref="ProductRegistration.SupportsPing"/>
 	public override bool SupportsPing { get; } = false;
 
diff --git a/src/Elastic.Transport/Products/Elasticsearch/ElasticsearchProductRegistration.cs b/src/Elastic.Transport/Products/Elasticsearch/ElasticsearchProductRegistration.cs
index f104cbc..8e2beb2 100644
--- a/src/Elastic.Transport/Products/Elasticsearch/ElasticsearchProductRegistration.cs
+++ b/src/Elastic.Transport/Products/Elasticsearch/ElasticsearchProductRegistration.cs
@@ -34,10 +34,13 @@ public class ElasticsearchProductRegistration : ProductRegistration
 	public ElasticsearchProductRegistration(Type markerType) : this()
 	{
 		var clientVersionInfo = ReflectionVersionInfo.Create(markerType);
-		_metaHeaderProvider = new DefaultMetaHeaderProvider(clientVersionInfo, "es");
+
+		var identifier = ServiceIdentifier;
+		if (!string.IsNullOrEmpty(identifier))
+			_metaHeaderProvider = new DefaultMetaHeaderProvider(clientVersionInfo, identifier);
 
 		// Only set this if we have a version.
-		// If we don't have a version we won't apply the vendor-based REST API compatibilty Accept header.
+		// If we don't have a version we won't apply the vendor-based REST API compatibility Accept header.
 		if (clientVersionInfo.Version.Major > 0)
 			_clientMajorVersion = clientVersionInfo.Version.Major;
 	}
@@ -48,6 +51,9 @@ public ElasticsearchProductRegistration(Type markerType) : this()
 	/// <inheritdoc cref="ProductRegistration.Name"/>
 	public override string Name { get; } = "elasticsearch-net";
 
+	/// <inheritdoc cref="ProductRegistration.ServiceIdentifier"/>
+	public override string? ServiceIdentifier => "es";
+
 	/// <inheritdoc cref="ProductRegistration.SupportsPing"/>
 	public override bool SupportsPing { get; } = true;
 
diff --git a/src/Elastic.Transport/Products/ProductRegistration.cs b/src/Elastic.Transport/Products/ProductRegistration.cs
index 278bf54..95da739 100644
--- a/src/Elastic.Transport/Products/ProductRegistration.cs
+++ b/src/Elastic.Transport/Products/ProductRegistration.cs
@@ -34,6 +34,11 @@ public abstract class ProductRegistration
 	/// </summary>
 	public abstract string Name { get; }
 
+	/// <summary>
+	/// An optional service-identifier string that is used in metadata headers.
+	/// </summary>
+	public abstract string? ServiceIdentifier { get; }
+
 	/// <summary>
 	/// Whether the product <see cref="HttpTransport{TConnectionSettings}"/> will call out to supports ping endpoints
 	/// </summary>