feat: support VertexAI provider (#153)

* support: vertexai

fix

fix

set default for vertexai

added comment

fix

fix

* create schema

* fix README.md

* fix order

* added pupularity

* set tools if tools is exists

restore commentout

* fix comment

* set summarizer model

3 files changed, 51 insertions, 6 deletions

diff --git a/internal/llm/provider/gemini.go b/internal/llm/provider/gemini.go
index cc97463d4..8b8e33698 100644
--- a/internal/llm/provider/gemini.go
+++ b/internal/llm/provider/gemini.go
@@ -176,13 +176,16 @@ func (g *geminiClient) send(ctx context.Context, messages []message.Message, too
 
 	history := geminiMessages[:len(geminiMessages)-1] // All but last message
 	lastMsg := geminiMessages[len(geminiMessages)-1]
-	chat, _ := g.client.Chats.Create(ctx, g.providerOptions.model.APIModel, &genai.GenerateContentConfig{
+	config := &genai.GenerateContentConfig{
 		MaxOutputTokens: int32(g.providerOptions.maxTokens),
 		SystemInstruction: &genai.Content{
 			Parts: []*genai.Part{{Text: g.providerOptions.systemMessage}},
 		},
-		Tools: g.convertTools(tools),
-	}, history)
+	}
+	if len(tools) > 0 {
+		config.Tools = g.convertTools(tools)
+	}
+	chat, _ := g.client.Chats.Create(ctx, g.providerOptions.model.APIModel, config, history)
 
 	attempts := 0
 	for {
@@ -262,13 +265,16 @@ func (g *geminiClient) stream(ctx context.Context, messages []message.Message, t
 
 	history := geminiMessages[:len(geminiMessages)-1] // All but last message
 	lastMsg := geminiMessages[len(geminiMessages)-1]
-	chat, _ := g.client.Chats.Create(ctx, g.providerOptions.model.APIModel, &genai.GenerateContentConfig{
+	config := &genai.GenerateContentConfig{
 		MaxOutputTokens: int32(g.providerOptions.maxTokens),
 		SystemInstruction: &genai.Content{
 			Parts: []*genai.Part{{Text: g.providerOptions.systemMessage}},
 		},
-		Tools: g.convertTools(tools),
-	}, history)
+	}
+	if len(tools) > 0 {
+		config.Tools = g.convertTools(tools)
+	}
+	chat, _ := g.client.Chats.Create(ctx, g.providerOptions.model.APIModel, config, history)
 
 	attempts := 0
 	eventChan := make(chan ProviderEvent)
diff --git a/internal/llm/provider/provider.go b/internal/llm/provider/provider.go
index 6f2a20bd9..f21e051c2 100644
--- a/internal/llm/provider/provider.go
+++ b/internal/llm/provider/provider.go
@@ -123,6 +123,11 @@ func NewProvider(providerName models.ModelProvider, opts ...ProviderClientOption
 			options: clientOptions,
 			client:  newAzureClient(clientOptions),
 		}, nil
+	case models.ProviderVertexAI:
+		return &baseProvider[VertexAIClient]{
+			options: clientOptions,
+			client:  newVertexAIClient(clientOptions),
+		}, nil
 	case models.ProviderOpenRouter:
 		clientOptions.openaiOptions = append(clientOptions.openaiOptions,
 			WithOpenAIBaseURL("https://openrouter.ai/api/v1"),
diff --git a/internal/llm/provider/vertexai.go b/internal/llm/provider/vertexai.go
new file mode 100644
index 000000000..2a13a9572
--- /dev/null
+++ b/internal/llm/provider/vertexai.go
@@ -0,0 +1,34 @@
+package provider
+
+import (
+	"context"
+	"os"
+
+	"github.com/opencode-ai/opencode/internal/logging"
+	"google.golang.org/genai"
+)
+
+type VertexAIClient ProviderClient
+
+func newVertexAIClient(opts providerClientOptions) VertexAIClient {
+	geminiOpts := geminiOptions{}
+	for _, o := range opts.geminiOptions {
+		o(&geminiOpts)
+	}
+
+	client, err := genai.NewClient(context.Background(), &genai.ClientConfig{
+		Project:  os.Getenv("VERTEXAI_PROJECT"),
+		Location: os.Getenv("VERTEXAI_LOCATION"),
+		Backend:  genai.BackendVertexAI,
+	})
+	if err != nil {
+		logging.Error("Failed to create VertexAI client", "error", err)
+		return nil
+	}
+
+	return &geminiClient{
+		providerOptions: opts,
+		options:         geminiOpts,
+		client:          client,
+	}
+}