diff --git a/Makefile b/Makefile
index 8a90abff0..7886badbb 100644
--- a/Makefile
+++ b/Makefile
@@ -127,7 +127,7 @@ install-tools: \
 #   module (it's linked into the api).
 
 # Where all generated builtin plugin code should go.
-pGen=api/builtins
+pGen=api/internal/builtins
 # Where the builtin Go plugin modules live.
 pSrc=plugin/builtin
 
diff --git a/api/builtins/builtins.go b/api/builtins/builtins.go
new file mode 100644
index 000000000..ae59f3779
--- /dev/null
+++ b/api/builtins/builtins.go
@@ -0,0 +1,49 @@
+// Copyright 2021 The Kubernetes Authors.
+// SPDX-License-Identifier: Apache-2.0
+
+// Deprecated: Package api/builtins will not be available in API v1.
+package builtins
+
+import (
+	internal "sigs.k8s.io/kustomize/api/internal/builtins"
+)
+
+type (
+	AnnotationsTransformerPlugin         = internal.AnnotationsTransformerPlugin
+	ConfigMapGeneratorPlugin             = internal.ConfigMapGeneratorPlugin
+	HashTransformerPlugin                = internal.HashTransformerPlugin
+	HelmChartInflationGeneratorPlugin    = internal.HelmChartInflationGeneratorPlugin
+	IAMPolicyGeneratorPlugin             = internal.IAMPolicyGeneratorPlugin
+	ImageTagTransformerPlugin            = internal.ImageTagTransformerPlugin
+	LabelTransformerPlugin               = internal.LabelTransformerPlugin
+	LegacyOrderTransformerPlugin         = internal.LegacyOrderTransformerPlugin
+	NamespaceTransformerPlugin           = internal.NamespaceTransformerPlugin
+	PatchJson6902TransformerPlugin       = internal.PatchJson6902TransformerPlugin
+	PatchStrategicMergeTransformerPlugin = internal.PatchStrategicMergeTransformerPlugin
+	PatchTransformerPlugin               = internal.PatchTransformerPlugin
+	PrefixSuffixTransformerPlugin        = internal.PrefixSuffixTransformerPlugin
+	ReplacementTransformerPlugin         = internal.ReplacementTransformerPlugin
+	ReplicaCountTransformerPlugin        = internal.ReplicaCountTransformerPlugin
+	SecretGeneratorPlugin                = internal.SecretGeneratorPlugin
+	ValueAddTransformerPlugin            = internal.ValueAddTransformerPlugin
+)
+
+var (
+	NewAnnotationsTransformerPlugin         = internal.NewAnnotationsTransformerPlugin
+	NewConfigMapGeneratorPlugin             = internal.NewConfigMapGeneratorPlugin
+	NewHashTransformerPlugin                = internal.NewHashTransformerPlugin
+	NewHelmChartInflationGeneratorPlugin    = internal.NewHelmChartInflationGeneratorPlugin
+	NewIAMPolicyGeneratorPlugin             = internal.NewIAMPolicyGeneratorPlugin
+	NewImageTagTransformerPlugin            = internal.NewImageTagTransformerPlugin
+	NewLabelTransformerPlugin               = internal.NewLabelTransformerPlugin
+	NewLegacyOrderTransformerPlugin         = internal.NewLegacyOrderTransformerPlugin
+	NewNamespaceTransformerPlugin           = internal.NewNamespaceTransformerPlugin
+	NewPatchJson6902TransformerPlugin       = internal.NewPatchJson6902TransformerPlugin
+	NewPatchStrategicMergeTransformerPlugin = internal.NewPatchStrategicMergeTransformerPlugin
+	NewPatchTransformerPlugin               = internal.NewPatchTransformerPlugin
+	NewPrefixSuffixTransformerPlugin        = internal.NewPrefixSuffixTransformerPlugin
+	NewReplacementTransformerPlugin         = internal.NewReplacementTransformerPlugin
+	NewReplicaCountTransformerPlugin        = internal.NewReplicaCountTransformerPlugin
+	NewSecretGeneratorPlugin                = internal.NewSecretGeneratorPlugin
+	NewValueAddTransformerPlugin            = internal.NewValueAddTransformerPlugin
+)
diff --git a/api/builtins/AnnotationsTransformer.go b/api/internal/builtins/AnnotationsTransformer.go
similarity index 100%
rename from api/builtins/AnnotationsTransformer.go
rename to api/internal/builtins/AnnotationsTransformer.go
diff --git a/api/builtins/ConfigMapGenerator.go b/api/internal/builtins/ConfigMapGenerator.go
similarity index 100%
rename from api/builtins/ConfigMapGenerator.go
rename to api/internal/builtins/ConfigMapGenerator.go
diff --git a/api/builtins/HashTransformer.go b/api/internal/builtins/HashTransformer.go
similarity index 100%
rename from api/builtins/HashTransformer.go
rename to api/internal/builtins/HashTransformer.go
diff --git a/api/builtins/HelmChartInflationGenerator.go b/api/internal/builtins/HelmChartInflationGenerator.go
similarity index 100%
rename from api/builtins/HelmChartInflationGenerator.go
rename to api/internal/builtins/HelmChartInflationGenerator.go
diff --git a/api/builtins/IAMPolicyGenerator.go b/api/internal/builtins/IAMPolicyGenerator.go
similarity index 100%
rename from api/builtins/IAMPolicyGenerator.go
rename to api/internal/builtins/IAMPolicyGenerator.go
diff --git a/api/builtins/ImageTagTransformer.go b/api/internal/builtins/ImageTagTransformer.go
similarity index 100%
rename from api/builtins/ImageTagTransformer.go
rename to api/internal/builtins/ImageTagTransformer.go
diff --git a/api/builtins/LabelTransformer.go b/api/internal/builtins/LabelTransformer.go
similarity index 100%
rename from api/builtins/LabelTransformer.go
rename to api/internal/builtins/LabelTransformer.go
diff --git a/api/builtins/LegacyOrderTransformer.go b/api/internal/builtins/LegacyOrderTransformer.go
similarity index 100%
rename from api/builtins/LegacyOrderTransformer.go
rename to api/internal/builtins/LegacyOrderTransformer.go
diff --git a/api/builtins/NamespaceTransformer.go b/api/internal/builtins/NamespaceTransformer.go
similarity index 100%
rename from api/builtins/NamespaceTransformer.go
rename to api/internal/builtins/NamespaceTransformer.go
diff --git a/api/builtins/PatchJson6902Transformer.go b/api/internal/builtins/PatchJson6902Transformer.go
similarity index 100%
rename from api/builtins/PatchJson6902Transformer.go
rename to api/internal/builtins/PatchJson6902Transformer.go
diff --git a/api/builtins/PatchStrategicMergeTransformer.go b/api/internal/builtins/PatchStrategicMergeTransformer.go
similarity index 100%
rename from api/builtins/PatchStrategicMergeTransformer.go
rename to api/internal/builtins/PatchStrategicMergeTransformer.go
diff --git a/api/builtins/PatchTransformer.go b/api/internal/builtins/PatchTransformer.go
similarity index 100%
rename from api/builtins/PatchTransformer.go
rename to api/internal/builtins/PatchTransformer.go
diff --git a/api/builtins/PrefixSuffixTransformer.go b/api/internal/builtins/PrefixSuffixTransformer.go
similarity index 100%
rename from api/builtins/PrefixSuffixTransformer.go
rename to api/internal/builtins/PrefixSuffixTransformer.go
diff --git a/api/builtins/ReplacementTransformer.go b/api/internal/builtins/ReplacementTransformer.go
similarity index 100%
rename from api/builtins/ReplacementTransformer.go
rename to api/internal/builtins/ReplacementTransformer.go
diff --git a/api/builtins/ReplicaCountTransformer.go b/api/internal/builtins/ReplicaCountTransformer.go
similarity index 100%
rename from api/builtins/ReplicaCountTransformer.go
rename to api/internal/builtins/ReplicaCountTransformer.go
diff --git a/api/builtins/SecretGenerator.go b/api/internal/builtins/SecretGenerator.go
similarity index 100%
rename from api/builtins/SecretGenerator.go
rename to api/internal/builtins/SecretGenerator.go
diff --git a/api/builtins/ValueAddTransformer.go b/api/internal/builtins/ValueAddTransformer.go
similarity index 100%
rename from api/builtins/ValueAddTransformer.go
rename to api/internal/builtins/ValueAddTransformer.go
diff --git a/api/builtins/doc.go b/api/internal/builtins/doc.go
similarity index 100%
rename from api/builtins/doc.go
rename to api/internal/builtins/doc.go
diff --git a/api/internal/plugins/builtinhelpers/builtins.go b/api/internal/plugins/builtinhelpers/builtins.go
index 7d5e8fce1..416ce5ec0 100644
--- a/api/internal/plugins/builtinhelpers/builtins.go
+++ b/api/internal/plugins/builtinhelpers/builtins.go
@@ -4,7 +4,7 @@
 package builtinhelpers
 
 import (
-	"sigs.k8s.io/kustomize/api/builtins"
+	"sigs.k8s.io/kustomize/api/internal/builtins"
 	"sigs.k8s.io/kustomize/api/resmap"
 )
 
diff --git a/api/internal/target/kusttarget.go b/api/internal/target/kusttarget.go
index d2929a03f..85f25165f 100644
--- a/api/internal/target/kusttarget.go
+++ b/api/internal/target/kusttarget.go
@@ -11,9 +11,9 @@ import (
 
 	"github.com/pkg/errors"
 
-	"sigs.k8s.io/kustomize/api/builtins"
 	"sigs.k8s.io/kustomize/api/ifc"
 	"sigs.k8s.io/kustomize/api/internal/accumulator"
+	"sigs.k8s.io/kustomize/api/internal/builtins"
 	"sigs.k8s.io/kustomize/api/internal/plugins/builtinconfig"
 	"sigs.k8s.io/kustomize/api/internal/plugins/builtinhelpers"
 	"sigs.k8s.io/kustomize/api/internal/plugins/loader"
diff --git a/api/krusty/kustomizer.go b/api/krusty/kustomizer.go
index ea67c5e6a..c5dda8a1b 100644
--- a/api/krusty/kustomizer.go
+++ b/api/krusty/kustomizer.go
@@ -7,7 +7,7 @@ import (
 	"fmt"
 	"path/filepath"
 
-	"sigs.k8s.io/kustomize/api/builtins"
+	"sigs.k8s.io/kustomize/api/internal/builtins"
 	pLdr "sigs.k8s.io/kustomize/api/internal/plugins/loader"
 	"sigs.k8s.io/kustomize/api/internal/target"
 	"sigs.k8s.io/kustomize/api/konfig"
diff --git a/cmd/pluginator/internal/builtinplugin/builtinplugin.go b/cmd/pluginator/internal/builtinplugin/builtinplugin.go
index cad21c83e..809f74618 100644
--- a/cmd/pluginator/internal/builtinplugin/builtinplugin.go
+++ b/cmd/pluginator/internal/builtinplugin/builtinplugin.go
@@ -141,7 +141,7 @@ func newWriter(r string) (*writer, error) {
 //   $HOME/kustomize/api/builtins
 func makeOutputFileName(root string) string {
 	return filepath.Join(
-		"..", "..", "..", "api", packageForGeneratedCode, root+".go")
+		"..", "..", "..", "api/internal", packageForGeneratedCode, root+".go")
 }
 
 func (w *writer) Close() error {