diff --git a/packages/types/src/providers/vertex.ts b/packages/types/src/providers/vertex.ts
index 199b139ddd30..ba077a249226 100644
--- a/packages/types/src/providers/vertex.ts
+++ b/packages/types/src/providers/vertex.ts
@@ -165,7 +165,7 @@ export const vertexModels = {
 	},
 	"claude-sonnet-4@20250514": {
 		maxTokens: 8192,
-		contextWindow: 200_000,
+		contextWindow: 1_000_000,
 		supportsImages: true,
 		supportsComputerUse: true,
 		supportsPromptCache: true,
@@ -177,7 +177,7 @@ export const vertexModels = {
 	},
 	"claude-sonnet-4-5@20250929": {
 		maxTokens: 8192,
-		contextWindow: 200_000,
+		contextWindow: 1_000_000,
 		supportsImages: true,
 		supportsComputerUse: true,
 		supportsPromptCache: true,
diff --git a/src/api/providers/__tests__/anthropic-vertex.spec.ts b/src/api/providers/__tests__/anthropic-vertex.spec.ts
index 9d83f265c7c3..1217895c2771 100644
--- a/src/api/providers/__tests__/anthropic-vertex.spec.ts
+++ b/src/api/providers/__tests__/anthropic-vertex.spec.ts
@@ -691,6 +691,34 @@ describe("VertexHandler", () => {
 			expect(modelInfo.info.contextWindow).toBe(200_000)
 		})
 
+		it("should return 1M context window for Claude Sonnet 4", () => {
+			handler = new AnthropicVertexHandler({
+				apiModelId: "claude-sonnet-4@20250514",
+				vertexProjectId: "test-project",
+				vertexRegion: "us-central1",
+			})
+
+			const modelInfo = handler.getModel()
+			expect(modelInfo.id).toBe("claude-sonnet-4@20250514")
+			expect(modelInfo.info).toBeDefined()
+			expect(modelInfo.info.maxTokens).toBe(8192)
+			expect(modelInfo.info.contextWindow).toBe(1_000_000)
+		})
+
+		it("should return 1M context window for Claude Sonnet 4.5", () => {
+			handler = new AnthropicVertexHandler({
+				apiModelId: "claude-sonnet-4-5@20250929",
+				vertexProjectId: "test-project",
+				vertexRegion: "us-central1",
+			})
+
+			const modelInfo = handler.getModel()
+			expect(modelInfo.id).toBe("claude-sonnet-4-5@20250929")
+			expect(modelInfo.info).toBeDefined()
+			expect(modelInfo.info.maxTokens).toBe(8192)
+			expect(modelInfo.info.contextWindow).toBe(1_000_000)
+		})
+
 		it("honors custom maxTokens for thinking models", () => {
 			const handler = new AnthropicVertexHandler({
 				apiKey: "test-api-key",