diff --git a/README.md b/README.md
index 2891ae3..b76f3da 100644
--- a/README.md
+++ b/README.md
@@ -3,7 +3,7 @@
 Generate Git commit messages from staged diffs using your preferred LLM CLI.
 
 git-ai-commit does not talk to LLM APIs directly.
-Instead, it delegates generation to existing LLM CLIs such as Claude Code, Gemini, or Codex, so no API keys, SDKs, or vendor-specific integrations are required.
+Instead, it delegates generation to existing LLM CLIs such as Claude Code, Antigravity, or Codex, so no API keys, SDKs, or vendor-specific integrations are required.
 
 ## Install
 
@@ -132,7 +132,8 @@ git-ai-commit treats LLMs as external commands, not as APIs. This design avoids
 Supported engines:
 
 - `claude`
-- `gemini`
+- `agy` (Antigravity CLI)
+- `gemini` (deprecated — see note below)
 - `codex`
 
 Built-in defaults are applied when `engines.<name>.args` is not set.
@@ -141,7 +142,9 @@ For `claude`, defaults include:
 - `-p --model haiku`
 - `--settings "{\"attribution\":{\"commit\":\"\",\"pr\":\"\"}}"` (prevents automatic `Co-authored-by` metadata)
 
-If no engine is configured, auto-detection tries commands in this order: `claude` → `gemini` → `codex`. The first available command is used.
+If no engine is configured, auto-detection tries commands in this order: `claude` → `agy` → `gemini` → `codex`. The first available command is used.
+
+> **Gemini CLI deprecation:** Google is transitioning Gemini CLI to Antigravity CLI (`agy`). After **June 18, 2026**, Gemini CLI stops serving requests for Google AI Pro/Ultra subscribers and free users. Gemini CLI continues to work for users on Gemini Code Assist Standard/Enterprise or paid API keys. If you previously used `engine = "gemini"`, switch to `engine = "agy"`.
 
 Any other engine name is treated as a direct command and executed with the prompt on stdin.
 
diff --git a/internal/app/app_test.go b/internal/app/app_test.go
index 37e09de..f3a34bc 100644
--- a/internal/app/app_test.go
+++ b/internal/app/app_test.go
@@ -172,6 +172,20 @@ func TestSelectEngineGeminiDefault(t *testing.T) {
 	}
 }
 
+func TestSelectEngineAgyDefault(t *testing.T) {
+	cfg := config.Default()
+	cfg.DefaultEngine = "agy"
+	cfg.Engines = map[string]config.EngineConfig{}
+
+	_, command, err := selectEngine(cfg)
+	if err != nil {
+		t.Fatalf("selectEngine error: %v", err)
+	}
+	if command != "agy -p {{prompt}}" {
+		t.Fatalf("command = %q", command)
+	}
+}
+
 func TestSelectEngineCustomArgs(t *testing.T) {
 	cfg := config.Default()
 	cfg.DefaultEngine = "claude"
diff --git a/internal/config/config.go b/internal/config/config.go
index e35596c..541515a 100644
--- a/internal/config/config.go
+++ b/internal/config/config.go
@@ -56,6 +56,7 @@ var DefaultEngineArgs = map[string][]string{
 	"claude":       {"-p", "--model", "haiku", "--settings", "{\"attribution\":{\"commit\":\"\",\"pr\":\"\"}}", "--no-session-persistence"},
 	"cursor-agent": {"-p"},
 	"gemini":       {"-m", "gemini-2.5-flash", "-p", "{{prompt}}"},
+	"agy":          {"-p", "{{prompt}}"},
 }
 
 func Default() Config {
@@ -353,7 +354,7 @@ func LoadPromptPreset(name string) (string, error) {
 }
 
 func autodetectEngine() string {
-	candidates := []string{"claude", "gemini", "codex"}
+	candidates := []string{"claude", "agy", "gemini", "codex"}
 	for _, name := range candidates {
 		if _, err := exec.LookPath(name); err == nil {
 			return name
diff --git a/internal/config/config_test.go b/internal/config/config_test.go
index e27a69e..df51b19 100644
--- a/internal/config/config_test.go
+++ b/internal/config/config_test.go
@@ -82,6 +82,30 @@ func TestAutodetectEngineOrder(t *testing.T) {
 	})
 }
 
+func TestAutodetectEnginePrefersAgyOverGemini(t *testing.T) {
+	configHome := t.TempDir()
+	binDir := filepath.Join(configHome, "bin")
+	if err := os.MkdirAll(binDir, 0o755); err != nil {
+		t.Fatalf("mkdir bin: %v", err)
+	}
+	makeExecutable(t, binDir, "codex")
+	makeExecutable(t, binDir, "gemini")
+	makeExecutable(t, binDir, "agy")
+
+	t.Setenv("PATH", binDir)
+	t.Setenv("XDG_CONFIG_HOME", t.TempDir())
+
+	withDir(t, t.TempDir(), func() {
+		cfg, err := Load()
+		if err != nil {
+			t.Fatalf("Load error: %v", err)
+		}
+		if cfg.DefaultEngine != "agy" {
+			t.Fatalf("DefaultEngine = %q", cfg.DefaultEngine)
+		}
+	})
+}
+
 func makeExecutable(t *testing.T, dir, name string) {
 	t.Helper()
 	path := filepath.Join(dir, name)