diff --git a/go/plugins/googleai/googleai.go b/go/plugins/googleai/googleai.go
index 6c637c2323..1e360b2e62 100644
--- a/go/plugins/googleai/googleai.go
+++ b/go/plugins/googleai/googleai.go
@@ -39,19 +39,20 @@ var (
 	basicText = ai.ModelCapabilities{
 		Multiturn:  true,
 		Tools:      true,
-		SystemRole: true,
+		SystemRole: false,
 		Media:      false,
 	}
 
 	multimodal = ai.ModelCapabilities{
 		Multiturn:  true,
 		Tools:      true,
-		SystemRole: true,
+		SystemRole: false,
 		Media:      true,
 	}
 
 	knownCaps = map[string]ai.ModelCapabilities{
 		"gemini-1.0-pro":   basicText,
+		"gemini-1.5-pro":   multimodal,
 		"gemini-1.5-flash": multimodal,
 	}
 )
@@ -117,6 +118,17 @@ func DefineModel(name string, caps *ai.ModelCapabilities) (*ai.Model, error) {
 	return defineModel(name, mc), nil
 }
 
+// KnownModels returns a slice of all known model names.
+func KnownModels() []string {
+	keys := make([]string, len(knownCaps))
+	i := 0
+	for k := range knownCaps {
+		keys[i] = k
+		i++
+	}
+	return keys
+}
+
 // requires state.mu
 func defineModel(name string, caps ai.ModelCapabilities) *ai.Model {
 	meta := &ai.ModelMetadata{
diff --git a/go/plugins/vertexai/vertexai.go b/go/plugins/vertexai/vertexai.go
index cc08dc83d2..5a02cc520b 100644
--- a/go/plugins/vertexai/vertexai.go
+++ b/go/plugins/vertexai/vertexai.go
@@ -30,6 +30,28 @@ import (
 
 const provider = "vertexai"
 
+var (
+	basicText = ai.ModelCapabilities{
+		Multiturn:  true,
+		Tools:      true,
+		SystemRole: false,
+		Media:      false,
+	}
+
+	multimodal = ai.ModelCapabilities{
+		Multiturn:  true,
+		Tools:      true,
+		SystemRole: false,
+		Media:      true,
+	}
+
+	knownCaps = map[string]ai.ModelCapabilities{
+		"gemini-1.0-pro":   basicText,
+		"gemini-1.5-pro":   multimodal,
+		"gemini-1.5-flash": multimodal,
+	}
+)
+
 var state struct {
 	mu        sync.Mutex
 	initted   bool
@@ -72,20 +94,46 @@ func Init(ctx context.Context, projectID, location string) error {
 }
 
 // DefineModel defines a model with the given name.
-func DefineModel(name string) *ai.Model {
+func DefineModel(name string, caps *ai.ModelCapabilities) (*ai.Model, error) {
 	state.mu.Lock()
 	defer state.mu.Unlock()
 	if !state.initted {
 		panic("vertexai.Init not called")
 	}
+	var mc ai.ModelCapabilities
+	if caps == nil {
+		var ok bool
+		mc, ok = knownCaps[name]
+		if !ok {
+			return nil, fmt.Errorf("vertextai.DefineModel: called with unknown model %q and nil ModelCapabilities", name)
+		}
+	} else {
+		mc = *caps
+	}
+
 	meta := &ai.ModelMetadata{
-		Label: "Vertex AI - " + name,
-		Supports: ai.ModelCapabilities{
-			Multiturn: true,
-		},
+		Label:    "Vertex AI - " + name,
+		Supports: mc,
 	}
 	g := &generator{model: name, client: state.gclient}
-	return ai.DefineModel(provider, name, meta, g.generate)
+	return ai.DefineModel(provider, name, meta, g.generate), nil
+}
+
+// IsKnownModel reports whether a model is known to this plugin.
+func IsKnownModel(name string) bool {
+	_, ok := knownCaps[name]
+	return ok
+}
+
+// KnownModels returns a slice of all known model names.
+func KnownModels() []string {
+	keys := make([]string, len(knownCaps))
+	i := 0
+	for k := range knownCaps {
+		keys[i] = k
+		i++
+	}
+	return keys
 }
 
 // DefineModel defines an embedder with the given name.
diff --git a/go/plugins/vertexai/vertexai_test.go b/go/plugins/vertexai/vertexai_test.go
index c2900be4f7..9ade6d89ea 100644
--- a/go/plugins/vertexai/vertexai_test.go
+++ b/go/plugins/vertexai/vertexai_test.go
@@ -44,7 +44,10 @@ func TestLive(t *testing.T) {
 	if err != nil {
 		t.Fatal(err)
 	}
-	model := vertexai.DefineModel(modelName)
+	model, err := vertexai.DefineModel(modelName, nil)
+	if err != nil {
+		t.Fatal(err)
+	}
 	embedder := vertexai.DefineEmbedder(embedderName)
 
 	toolDef := &ai.ToolDefinition{
diff --git a/go/samples/coffee-shop/main.go b/go/samples/coffee-shop/main.go
index 4fc0d21518..82d5cb08da 100755
--- a/go/samples/coffee-shop/main.go
+++ b/go/samples/coffee-shop/main.go
@@ -104,19 +104,21 @@ func main() {
 		fmt.Fprintln(os.Stderr, "You can get an API key at https://ai.google.dev.")
 		os.Exit(1)
 	}
-	err := googleai.Init(context.Background(), apiKey)
-	if err != nil {
+	if err := googleai.Init(context.Background(), apiKey); err != nil {
 		log.Fatal(err)
 	}
+	for _, mname := range googleai.KnownModels() {
+		_, err := googleai.DefineModel(mname, nil)
+		if err != nil {
+			log.Fatal(err)
+		}
+	}
 
 	r := &jsonschema.Reflector{
 		AllowAdditionalProperties: false,
 		DoNotReference:            true,
 	}
-	g, err := googleai.DefineModel("gemini-1.5-pro", nil)
-	if err != nil {
-		log.Fatal(err)
-	}
+	g := googleai.Model("gemini-1.5-flash")
 	simpleGreetingPrompt, err := dotprompt.Define("simpleGreeting", simpleGreetingPromptTemplate,
 		dotprompt.Config{
 			Model:        g,
diff --git a/go/samples/menu/main.go b/go/samples/menu/main.go
index 12c8badeef..a5104725b8 100644
--- a/go/samples/menu/main.go
+++ b/go/samples/menu/main.go
@@ -78,8 +78,14 @@ func main() {
 	if err != nil {
 		log.Fatal(err)
 	}
-	model := vertexai.DefineModel("gemini-1.0-pro")
-	visionModel := vertexai.DefineModel("gemini-1.0-pro-vision")
+	model, err := vertexai.DefineModel("gemini-1.0-pro", nil)
+	if err != nil {
+		log.Fatal(err)
+	}
+	visionModel, err := vertexai.DefineModel("gemini-1.5-flash", nil)
+	if err != nil {
+		log.Fatal(err)
+	}
 	embedder := vertexai.DefineEmbedder("textembedding-gecko")
 	if err := setup01(ctx, model); err != nil {
 		log.Fatal(err)
@@ -99,6 +105,9 @@ func main() {
 	indexer, retriever, err := localvec.DefineIndexerAndRetriever("go-menu_items", localvec.Config{
 		Embedder: embedder,
 	})
+	if err != nil {
+		log.Fatal(err)
+	}
 	if err := setup04(ctx, indexer, retriever, model); err != nil {
 		log.Fatal(err)
 	}