diff --git a/go/internal/doc-snippets/dotprompt.go b/go/internal/doc-snippets/dotprompt.go
index bd688db997..f7262d66b2 100644
--- a/go/internal/doc-snippets/dotprompt.go
+++ b/go/internal/doc-snippets/dotprompt.go
@@ -35,9 +35,9 @@ func dot01() error {
 	ctx := context.Background()
 
 	// The .prompt file specifies vertexai/gemini-1.5-pro, so make sure it's set
-	// up:
-	projectID := os.Getenv("GCLOUD_PROJECT")
-	vertexai.Init(ctx, projectID, "us-central1")
+	// up.
+	// Default to the project in GCLOUD_PROJECT and the location "us-central1".
+	vertexai.Init(ctx, nil)
 	vertexai.DefineModel("gemini-1.5-pro", nil)
 
 	type GreetingPromptInput struct {
diff --git a/go/internal/doc-snippets/init/main.go b/go/internal/doc-snippets/init/main.go
index 0343558844..62c2c81c0a 100644
--- a/go/internal/doc-snippets/init/main.go
+++ b/go/internal/doc-snippets/init/main.go
@@ -30,11 +30,11 @@ import (
 func main() {
 	ctx := context.Background()
 
-	// Initialize the Google AI plugin. When you pass an empty string for the
-	// apiKey parameter, the Google AI plugin will use the value from the
+	// Initialize the Google AI plugin. When you pass nil for the
+	// Config parameter, the Google AI plugin will get the API key from the
 	// GOOGLE_GENAI_API_KEY environment variable, which is the recommended
 	// practice.
-	if err := googleai.Init(ctx, ""); err != nil {
+	if err := googleai.Init(ctx, nil); err != nil {
 		log.Fatal(err)
 	}
 
diff --git a/go/internal/doc-snippets/models.go b/go/internal/doc-snippets/models.go
index e7258b6f54..dd3262271d 100644
--- a/go/internal/doc-snippets/models.go
+++ b/go/internal/doc-snippets/models.go
@@ -34,12 +34,13 @@ var gemini15pro *ai.Model
 
 func m1() error {
 	// !+init
-	projectID := os.Getenv("GCLOUD_PROJECT")
-	if err := vertexai.Init(ctx, projectID, "us-central1"); err != nil {
+	// Default to the value of GCLOUD_PROJECT for the project,
+	// and "us-central1" for the location.
+	// To specify these values directly, pass a vertexai.Config value to Init.
+	if err := vertexai.Init(ctx, nil); err != nil {
 		return err
 	}
 	// !-init
-	_ = projectID
 
 	// !+model
 	gemini15pro := vertexai.Model("gemini-1.5-pro")
diff --git a/go/plugins/googleai/googleai.go b/go/plugins/googleai/googleai.go
index 8b192542a4..69bf559f63 100644
--- a/go/plugins/googleai/googleai.go
+++ b/go/plugins/googleai/googleai.go
@@ -59,10 +59,23 @@ var (
 	knownEmbedders = []string{"text-embedding-004", "embedding-001"}
 )
 
+// Config is the configuration for the plugin.
+type Config struct {
+	// The API key to access the service.
+	// If empty, the values of the environment variables GOOGLE_GENAI_API_KEY
+	// and GOOGLE_API_KEY will be consulted, in that order.
+	APIKey string
+	// Options to the Google AI client.
+	ClientOptions []option.ClientOption
+}
+
 // Init initializes the plugin and all known models and embedders.
 // After calling Init, you may call [DefineModel] and [DefineEmbedder] to create
 // and register any additional generative models and embedders
-func Init(ctx context.Context, apiKey string) (err error) {
+func Init(ctx context.Context, cfg *Config) (err error) {
+	if cfg == nil {
+		cfg = &Config{}
+	}
 	state.mu.Lock()
 	defer state.mu.Unlock()
 	if state.initted {
@@ -74,6 +87,7 @@ func Init(ctx context.Context, apiKey string) (err error) {
 		}
 	}()
 
+	apiKey := cfg.APIKey
 	if apiKey == "" {
 		apiKey = os.Getenv("GOOGLE_GENAI_API_KEY")
 		if apiKey == "" {
@@ -84,7 +98,8 @@ func Init(ctx context.Context, apiKey string) (err error) {
 		}
 	}
 
-	client, err := genai.NewClient(ctx, option.WithAPIKey(apiKey))
+	opts := append([]option.ClientOption{option.WithAPIKey(apiKey)}, cfg.ClientOptions...)
+	client, err := genai.NewClient(ctx, opts...)
 	if err != nil {
 		return err
 	}
diff --git a/go/plugins/googleai/googleai_test.go b/go/plugins/googleai/googleai_test.go
index b2656d1cb8..45317d2e26 100644
--- a/go/plugins/googleai/googleai_test.go
+++ b/go/plugins/googleai/googleai_test.go
@@ -42,7 +42,7 @@ func TestLive(t *testing.T) {
 		t.Skip("-all provided")
 	}
 	ctx := context.Background()
-	err := googleai.Init(ctx, *apiKey)
+	err := googleai.Init(ctx, &googleai.Config{APIKey: *apiKey})
 	if err != nil {
 		t.Fatal(err)
 	}
diff --git a/go/plugins/vertexai/vertexai.go b/go/plugins/vertexai/vertexai.go
index a822189a59..ea472dc5cf 100644
--- a/go/plugins/vertexai/vertexai.go
+++ b/go/plugins/vertexai/vertexai.go
@@ -72,36 +72,53 @@ var state struct {
 	pclient   *aiplatform.PredictionClient
 }
 
+// Config is the configuration for the plugin.
+type Config struct {
+	// The cloud project to use for Vertex AI.
+	// If empty, the values of the environment variables GCLOUD_PROJECT
+	// and GOOGLE_CLOUD_PROJECT will be consulted, in that order.
+	ProjectID string
+	// The location of the Vertex AI service. The default is "us-central1".
+	Location string
+	// Options to the Vertex AI client.
+	ClientOptions []option.ClientOption
+}
+
 // Init initializes the plugin and all known models and embedders.
 // After calling Init, you may call [DefineModel] and [DefineEmbedder] to create
 // and register any additional generative models and embedders
-func Init(ctx context.Context, projectID, location string) error {
+func Init(ctx context.Context, cfg *Config) error {
+	if cfg == nil {
+		cfg = &Config{}
+	}
 	state.mu.Lock()
 	defer state.mu.Unlock()
 	if state.initted {
 		panic("vertexai.Init already called")
 	}
-	if projectID == "" {
-		projectID = os.Getenv("GCLOUD_PROJECT")
-		if projectID == "" {
-			projectID = os.Getenv("GOOGLE_CLOUD_PROJECT")
-		}
-		if projectID == "" {
-			return fmt.Errorf("vertexai.Init: Vertex AI requires setting GCLOUD_PROJECT or GOOGLE_CLOUD_PROJECT in the environment")
-		}
+
+	state.projectID = cfg.ProjectID
+	if state.projectID == "" {
+		state.projectID = os.Getenv("GCLOUD_PROJECT")
+	}
+	if state.projectID == "" {
+		state.projectID = os.Getenv("GOOGLE_CLOUD_PROJECT")
 	}
-	state.projectID = projectID
-	if location == "" {
-		location = "us-central1"
+	if state.projectID == "" {
+		return fmt.Errorf("vertexai.Init: Vertex AI requires setting GCLOUD_PROJECT or GOOGLE_CLOUD_PROJECT in the environment")
+	}
+
+	state.location = cfg.Location
+	if state.location == "" {
+		state.location = "us-central1"
 	}
-	state.location = location
 	var err error
 	// Client for Gemini SDK.
-	state.gclient, err = genai.NewClient(ctx, projectID, location)
+	state.gclient, err = genai.NewClient(ctx, state.projectID, state.location, cfg.ClientOptions...)
 	if err != nil {
 		return err
 	}
-	endpoint := fmt.Sprintf("%s-aiplatform.googleapis.com:443", location)
+	endpoint := fmt.Sprintf("%s-aiplatform.googleapis.com:443", state.location)
 	numConns := max(runtime.GOMAXPROCS(0), 4)
 	o := []option.ClientOption{
 		option.WithEndpoint(endpoint),
diff --git a/go/plugins/vertexai/vertexai_test.go b/go/plugins/vertexai/vertexai_test.go
index b8675d647c..4238d2fe75 100644
--- a/go/plugins/vertexai/vertexai_test.go
+++ b/go/plugins/vertexai/vertexai_test.go
@@ -39,7 +39,8 @@ func TestLive(t *testing.T) {
 	}
 	ctx := context.Background()
 	const modelName = "gemini-1.0-pro"
-	err := vertexai.Init(ctx, *projectID, *location)
+	const embedderName = "textembedding-gecko"
+	err := vertexai.Init(ctx, &vertexai.Config{ProjectID: *projectID, Location: *location})
 	if err != nil {
 		t.Fatal(err)
 	}
diff --git a/go/samples/coffee-shop/main.go b/go/samples/coffee-shop/main.go
index 1cb4f90cd5..1649e9c77f 100755
--- a/go/samples/coffee-shop/main.go
+++ b/go/samples/coffee-shop/main.go
@@ -97,7 +97,7 @@ type testAllCoffeeFlowsOutput struct {
 }
 
 func main() {
-	if err := googleai.Init(context.Background(), ""); err != nil {
+	if err := googleai.Init(context.Background(), nil); err != nil {
 		log.Fatal(err)
 	}
 
diff --git a/go/samples/menu/main.go b/go/samples/menu/main.go
index 42d6e3ba84..093c573519 100644
--- a/go/samples/menu/main.go
+++ b/go/samples/menu/main.go
@@ -16,7 +16,6 @@ package main
 
 import (
 	"context"
-	"fmt"
 	"log"
 	"os"
 
@@ -67,14 +66,8 @@ type textMenuQuestionInput struct {
 var textMenuQuestionInputSchema = jsonschema.Reflect(textMenuQuestionInput{})
 
 func main() {
-	projectID := os.Getenv("GCLOUD_PROJECT")
-	if projectID == "" {
-		fmt.Fprintln(os.Stderr, "menu example requires setting GCLOUD_PROJECT in the environment.")
-		os.Exit(1)
-	}
-
 	ctx := context.Background()
-	err := vertexai.Init(ctx, projectID, os.Getenv("GCLOUD_LOCATION"))
+	err := vertexai.Init(ctx, &vertexai.Config{Location: os.Getenv("GCLOUD_LOCATION")})
 	if err != nil {
 		log.Fatal(err)
 	}
diff --git a/go/samples/rag/main.go b/go/samples/rag/main.go
index 857cc59ff6..44c5a28735 100644
--- a/go/samples/rag/main.go
+++ b/go/samples/rag/main.go
@@ -38,7 +38,6 @@ import (
 	"context"
 	"fmt"
 	"log"
-	"os"
 	"strings"
 
 	"github.com/firebase/genkit/go/ai"
@@ -69,13 +68,7 @@ type simpleQaPromptInput struct {
 }
 
 func main() {
-	apiKey := os.Getenv("GOOGLE_GENAI_API_KEY")
-	if apiKey == "" {
-		fmt.Fprintln(os.Stderr, "rag example requires setting GOOGLE_GENAI_API_KEY in the environment.")
-		fmt.Fprintln(os.Stderr, "You can get an API key at https://ai.google.dev.")
-		os.Exit(1)
-	}
-	err := googleai.Init(context.Background(), apiKey)
+	err := googleai.Init(context.Background(), nil)
 	if err != nil {
 		log.Fatal(err)
 	}