aws
diff --git a/‎codegen/smithy-aws-go-codegen/src/main/java/software/amazon/smithy/aws/go/codegen/customization/AwsEndpointBuiltins.java
+31 b/‎codegen/smithy-aws-go-codegen/src/main/java/software/amazon/smithy/aws/go/codegen/customization/AwsEndpointBuiltins.java
+31
diff --git a/‎codegen/smithy-aws-go-codegen/src/main/resources/META-INF/services/software.amazon.smithy.go.codegen.integration.GoIntegration
+2-1 b/‎codegen/smithy-aws-go-codegen/src/main/resources/META-INF/services/software.amazon.smithy.go.codegen.integration.GoIntegration
+2-1
diff --git a/‎feature/dynamodbstreams/attributevalue/go_module_metadata.go
+1-1 b/‎feature/dynamodbstreams/attributevalue/go_module_metadata.go
+1-1
diff --git a/‎internal/protocoltest/awsrestjson/auth.go
+2-2 b/‎internal/protocoltest/awsrestjson/auth.go
+2-2
diff --git a/‎internal/protocoltest/ec2query/auth.go
+2-2 b/‎internal/protocoltest/ec2query/auth.go
+2-2
diff --git a/‎internal/protocoltest/jsonrpc10/auth.go
+2-2 b/‎internal/protocoltest/jsonrpc10/auth.go
+2-2
diff --git a/‎internal/protocoltest/query/auth.go
+2-2 b/‎internal/protocoltest/query/auth.go
+2-2
diff --git a/‎internal/protocoltest/restxml/auth.go
+2-2 b/‎internal/protocoltest/restxml/auth.go
+2-2
diff --git a/‎internal/protocoltest/restxmlwithnamespace/api_client.go
+10-9 b/‎internal/protocoltest/restxmlwithnamespace/api_client.go
+10-9
diff --git a/‎internal/protocoltest/restxmlwithnamespace/auth.go
+2-2 b/‎internal/protocoltest/restxmlwithnamespace/auth.go
+2-2
diff --git a/‎internal/protocoltest/smithyrpcv2cbor/api_client.go
+9-8 b/‎internal/protocoltest/smithyrpcv2cbor/api_client.go
+9-8
diff --git a/‎internal/protocoltest/smithyrpcv2cbor/auth.go
+2-2 b/‎internal/protocoltest/smithyrpcv2cbor/auth.go
+2-2
diff --git a/‎internal/protocoltest/smithyrpcv2cbor/options.go
+3 b/‎internal/protocoltest/smithyrpcv2cbor/options.go
+3
diff --git a/‎service/accessanalyzer/api_client.go
+42-9 b/‎service/accessanalyzer/api_client.go
+42-9
@@ -5,10 +5,13 @@
 import software.amazon.smithy.go.codegen.GoDelegator;
 import software.amazon.smithy.go.codegen.GoSettings;
 import software.amazon.smithy.go.codegen.GoWriter;
+import software.amazon.smithy.go.codegen.SmithyGoTypes;
 import software.amazon.smithy.go.codegen.integration.GoIntegration;
 import software.amazon.smithy.go.codegen.integration.RuntimeClientPlugin;
 import software.amazon.smithy.model.Model;
+import software.amazon.smithy.rulesengine.traits.EndpointRuleSetTrait;
 import software.amazon.smithy.utils.ListUtils;
+import software.amazon.smithy.utils.MapUtils;
 
 import java.util.List;
 
@@ -36,6 +39,8 @@ public class AwsEndpointBuiltins implements GoIntegration {
             goTemplate("$T(options.UseARNRegion)", SdkGoTypes.Aws.Bool);
     private static final GoWriter.Writable BindAwsS3DisableMultiRegionAccessPoints =
             goTemplate("$T(options.DisableMultiRegionAccessPoints)", SdkGoTypes.Aws.Bool);
+    private static final GoWriter.Writable BindAccountID =
+            goTemplate("resolveAccountID(getIdentity(ctx), options.AccountIDEndpointMode)");
 
     @Override
     public List<RuntimeClientPlugin> getClientPlugins() {
@@ -49,12 +54,38 @@ public List<RuntimeClientPlugin> getClientPlugins() {
                 .addEndpointBuiltinBinding("AWS::S3::UseArnRegion", BindAwsS3UseArnRegion)
                 .addEndpointBuiltinBinding("AWS::S3::DisableMultiRegionAccessPoints", BindAwsS3DisableMultiRegionAccessPoints)
                 .addEndpointBuiltinBinding("AWS::S3Control::UseArnRegion", BindAwsS3UseArnRegion)
+                .addEndpointBuiltinBinding("AWS::Auth::AccountId", BindAccountID)
                 .build());
     }
 
     @Override
     public void writeAdditionalFiles(GoSettings settings, Model model, SymbolProvider symbolProvider, GoDelegator goDelegator) {
         goDelegator.useFileWriter("endpoints.go", settings.getModuleName(), builtinBindingSource());
+        if (!settings.getService(model).hasTrait(EndpointRuleSetTrait.class)) {
+            return;
+        }
+        goDelegator.useShapeWriter(settings.getService(model), goTemplate("""
+        func resolveAccountID(identity $auth:T, mode $accountIDEndpointMode:T) *string {
+            if mode == $aidModeDisabled:T {
+                return nil
+            }
+            
+            if ca, ok := identity.(*$credentialsAdapter:T); ok && ca.Credentials.AccountID != "" {
+                return $string:T(ca.Credentials.AccountID)
+            }
+            
+            return nil
+        }
+        """,
+                MapUtils.of(
+                        "auth", SmithyGoTypes.Auth.Identity,
+                        "accountIDEndpointMode", SdkGoTypes.Aws.AccountIDEndpointMode,
+                        "aidModeUnset", SdkGoTypes.Aws.AccountIDEndpointModeUnset,
+                        "aidModeDisabled", SdkGoTypes.Aws.AccountIDEndpointModeDisabled,
+                        "credentialsAdapter", SdkGoTypes.Internal.Auth.Smithy.CredentialsAdapter,
+                        "string", SdkGoTypes.Aws.String
+                )
+        ));
     }
 
     private GoWriter.Writable builtinBindingSource() {
 
@@ -76,4 +76,5 @@ software.amazon.smithy.aws.go.codegen.customization.CloudFrontKVSSigV4a
 software.amazon.smithy.aws.go.codegen.customization.BackfillProtocolTestServiceTrait
 software.amazon.smithy.go.codegen.integration.MiddlewareStackSnapshotTests
 software.amazon.smithy.aws.go.codegen.customization.s3.S3ExpiresShapeCustomization
-software.amazon.smithy.aws.go.codegen.ClockSkewGenerator
+software.amazon.smithy.aws.go.codegen.ClockSkewGenerator
+software.amazon.smithy.aws.go.codegen.customization.AccountIDEndpointRouting