diff --git a/internal/registry/model_definitions_test.go b/internal/registry/model_definitions_test.go
index 934802fb2c..a99e7987be 100644
--- a/internal/registry/model_definitions_test.go
+++ b/internal/registry/model_definitions_test.go
@@ -1,6 +1,9 @@
 package registry
 
-import "testing"
+import (
+	"slices"
+	"testing"
+)
 
 func TestGetStaticModelDefinitionsByChannelSupportsGeminiInteractions(t *testing.T) {
 	models := GetStaticModelDefinitionsByChannel("gemini-interactions")
@@ -42,6 +45,49 @@ func TestGeminiVertexModelsUseFlashLiteReleaseID(t *testing.T) {
 	t.Fatalf("Vertex models do not contain %q", releaseID)
 }
 
+func TestAntigravityModelsIncludeGemini38Flash(t *testing.T) {
+	modelsByID := make(map[string]*ModelInfo)
+	for _, model := range GetAntigravityModels() {
+		if model != nil {
+			modelsByID[model.ID] = model
+		}
+	}
+
+	tests := []struct {
+		id          string
+		description string
+	}{
+		{id: "gemini-3.8-flash-high", description: "Gemini 3.8 Flash (High)"},
+		{id: "gemini-3.8-flash-medium", description: "Gemini 3.8 Flash (Medium)"},
+	}
+	for _, tt := range tests {
+		t.Run(tt.id, func(t *testing.T) {
+			got := modelsByID[tt.id]
+			if got == nil {
+				t.Fatalf("Antigravity models do not contain %q", tt.id)
+			}
+			if got.OwnedBy != "antigravity" || got.Type != "antigravity" || got.Name != tt.id || got.DisplayName != "Gemini 3.8 Flash" || got.Description != tt.description {
+				t.Fatalf("Gemini 3.8 Flash identity metadata = %+v", got)
+			}
+			if got.ContextLength != 1048576 || got.MaxCompletionTokens != 65536 {
+				t.Fatalf("Gemini 3.8 Flash token limits = %d/%d, want 1048576/65536", got.ContextLength, got.MaxCompletionTokens)
+			}
+			if got.Thinking == nil || got.Thinking.Min != 1 || got.Thinking.Max != 65535 || !got.Thinking.DynamicAllowed {
+				t.Fatalf("Gemini 3.8 Flash thinking metadata = %+v", got.Thinking)
+			}
+			if want := []string{"low", "medium", "high"}; !slices.Equal(got.Thinking.Levels, want) {
+				t.Fatalf("Gemini 3.8 Flash thinking levels = %v, want %v", got.Thinking.Levels, want)
+			}
+			if want := []string{"text", "image", "audio", "video"}; !slices.Equal(got.SupportedInputModalities, want) {
+				t.Fatalf("Gemini 3.8 Flash input modalities = %v, want %v", got.SupportedInputModalities, want)
+			}
+			if want := []string{"text"}; !slices.Equal(got.SupportedOutputModalities, want) {
+				t.Fatalf("Gemini 3.8 Flash output modalities = %v, want %v", got.SupportedOutputModalities, want)
+			}
+		})
+	}
+}
+
 func TestWithXAIBuiltinsIncludesImage20(t *testing.T) {
 	models := WithXAIBuiltins(nil)
 	for _, model := range models {
diff --git a/internal/registry/models/models.json b/internal/registry/models/models.json
index 333a071cc0..2fc55de346 100644
--- a/internal/registry/models/models.json
+++ b/internal/registry/models/models.json
@@ -3445,6 +3445,66 @@
         "text"
       ]
     },
+    {
+      "id": "gemini-3.8-flash-high",
+      "object": "model",
+      "owned_by": "antigravity",
+      "type": "antigravity",
+      "display_name": "Gemini 3.8 Flash",
+      "name": "gemini-3.8-flash-high",
+      "description": "Gemini 3.8 Flash (High)",
+      "context_length": 1048576,
+      "max_completion_tokens": 65536,
+      "thinking": {
+        "min": 1,
+        "max": 65535,
+        "dynamic_allowed": true,
+        "levels": [
+          "low",
+          "medium",
+          "high"
+        ]
+      },
+      "supportedInputModalities": [
+        "text",
+        "image",
+        "audio",
+        "video"
+      ],
+      "supportedOutputModalities": [
+        "text"
+      ]
+    },
+    {
+      "id": "gemini-3.8-flash-medium",
+      "object": "model",
+      "owned_by": "antigravity",
+      "type": "antigravity",
+      "display_name": "Gemini 3.8 Flash",
+      "name": "gemini-3.8-flash-medium",
+      "description": "Gemini 3.8 Flash (Medium)",
+      "context_length": 1048576,
+      "max_completion_tokens": 65536,
+      "thinking": {
+        "min": 1,
+        "max": 65535,
+        "dynamic_allowed": true,
+        "levels": [
+          "low",
+          "medium",
+          "high"
+        ]
+      },
+      "supportedInputModalities": [
+        "text",
+        "image",
+        "audio",
+        "video"
+      ],
+      "supportedOutputModalities": [
+        "text"
+      ]
+    },
     {
       "id": "gemini-3-flash",
       "object": "model",