diff --git a/multitree/api_surface.go b/multitree/api_surface.go
new file mode 100644
index 0000000..f739a24
--- /dev/null
+++ b/multitree/api_surface.go
@@ -0,0 +1,119 @@
+// Copyright 2021 Google Inc. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package multitree
+
+import (
+	"android/soong/android"
+	"fmt"
+
+	"github.com/google/blueprint"
+)
+
+var (
+	pctx = android.NewPackageContext("android/soong/multitree")
+)
+
+func init() {
+	RegisterApiSurfaceBuildComponents(android.InitRegistrationContext)
+}
+
+var PrepareForTestWithApiSurface = android.FixtureRegisterWithContext(RegisterApiSurfaceBuildComponents)
+
+func RegisterApiSurfaceBuildComponents(ctx android.RegistrationContext) {
+	ctx.RegisterModuleType("api_surface", ApiSurfaceFactory)
+}
+
+type ApiSurface struct {
+	android.ModuleBase
+	ExportableModuleBase
+	properties apiSurfaceProperties
+
+	allOutputs    android.Paths
+	taggedOutputs map[string]android.Paths
+}
+
+type apiSurfaceProperties struct {
+	Contributions []string
+}
+
+func ApiSurfaceFactory() android.Module {
+	module := &ApiSurface{}
+	module.AddProperties(&module.properties)
+	android.InitAndroidModule(module)
+	InitExportableModule(module)
+	return module
+}
+
+func (surface *ApiSurface) DepsMutator(ctx android.BottomUpMutatorContext) {
+	if surface.properties.Contributions != nil {
+		ctx.AddVariationDependencies(nil, nil, surface.properties.Contributions...)
+	}
+
+}
+func (surface *ApiSurface) GenerateAndroidBuildActions(ctx android.ModuleContext) {
+	contributionFiles := make(map[string]android.Paths)
+	var allOutputs android.Paths
+	ctx.WalkDeps(func(child, parent android.Module) bool {
+		if contribution, ok := child.(ApiContribution); ok {
+			copied := contribution.CopyFilesWithTag(ctx)
+			for tag, files := range copied {
+				contributionFiles[child.Name()+"#"+tag] = files
+			}
+			for _, paths := range copied {
+				allOutputs = append(allOutputs, paths...)
+			}
+			return false // no transitive dependencies
+		}
+		return false
+	})
+
+	// phony target
+	ctx.Build(pctx, android.BuildParams{
+		Rule:   blueprint.Phony,
+		Output: android.PathForPhony(ctx, ctx.ModuleName()),
+		Inputs: allOutputs,
+	})
+
+	surface.allOutputs = allOutputs
+	surface.taggedOutputs = contributionFiles
+}
+
+func (surface *ApiSurface) OutputFiles(tag string) (android.Paths, error) {
+	if tag != "" {
+		return nil, fmt.Errorf("unknown tag: %q", tag)
+	}
+	return surface.allOutputs, nil
+}
+
+func (surface *ApiSurface) TaggedOutputs() map[string]android.Paths {
+	return surface.taggedOutputs
+}
+
+func (surface *ApiSurface) Exportable() bool {
+	return true
+}
+
+var _ android.OutputFileProducer = (*ApiSurface)(nil)
+var _ Exportable = (*ApiSurface)(nil)
+
+type ApiContribution interface {
+	// copy files necessaryt to construct an API surface
+	// For C, it will be map.txt and .h files
+	// For Java, it will be api.txt
+	CopyFilesWithTag(ctx android.ModuleContext) map[string]android.Paths // output paths
+
+	// Generate Android.bp in out/ to use the exported .txt files
+	// GenerateBuildFiles(ctx ModuleContext) Paths //output paths
+}