fix: handle global region correctly for Vertex AI Claude models

- Add custom baseURL for global region to use aiplatform.googleapis.com
- Prevents incorrect hostname construction (global-aiplatform.googleapis.com)
- Add comprehensive test coverage for global region scenarios

Fixes #8571

src/api/providers/__tests__/anthropic-vertex.spec.ts

@@ -62,8 +62,58 @@ describe("VertexHandler", () => {
 			expect(AnthropicVertex).toHaveBeenCalledWith({
 				projectId: "test-project",
 				region: "us-central1",
+				baseURL: undefined,
 			})
 		})
+
+		it("should use custom baseURL for global region", () => {
+			handler = new AnthropicVertexHandler({
+				apiModelId: "claude-3-5-sonnet-v2@20241022",
+				vertexProjectId: "test-project",
+				vertexRegion: "global",
+			})
+
+			expect(AnthropicVertex).toHaveBeenCalledWith({
+				projectId: "test-project",
+				region: "global",
+				baseURL: "https://aiplatform.googleapis.com/v1",
+			})
+		})
+
+		it("should use custom baseURL for global region with JSON credentials", () => {
+			const mockCredentials = JSON.stringify({ type: "service_account", project_id: "test" })
+			handler = new AnthropicVertexHandler({
+				apiModelId: "claude-3-5-sonnet-v2@20241022",
+				vertexProjectId: "test-project",
+				vertexRegion: "global",
+				vertexJsonCredentials: mockCredentials,
+			})
+
+			expect(AnthropicVertex).toHaveBeenCalledWith(
+				expect.objectContaining({
+					projectId: "test-project",
+					region: "global",
+					baseURL: "https://aiplatform.googleapis.com/v1",
+				}),
+			)
+		})
+
+		it("should use custom baseURL for global region with key file", () => {
+			handler = new AnthropicVertexHandler({
+				apiModelId: "claude-3-5-sonnet-v2@20241022",
+				vertexProjectId: "test-project",
+				vertexRegion: "global",
+				vertexKeyFile: "/path/to/keyfile.json",
+			})
+
+			expect(AnthropicVertex).toHaveBeenCalledWith(
+				expect.objectContaining({
+					projectId: "test-project",
+					region: "global",
+					baseURL: "https://aiplatform.googleapis.com/v1",
+				}),
+			)
+		})
 	})
 
 	describe("createMessage", () => {

src/api/providers/anthropic-vertex.ts

@@ -34,10 +34,16 @@ export class AnthropicVertexHandler extends BaseProvider implements SingleComple
 		const projectId = this.options.vertexProjectId ?? "not-provided"
 		const region = this.options.vertexRegion ?? "us-east5"
 
+		// For the "global" region, we need to use a custom base URL
+		// The default would be "global-aiplatform.googleapis.com" which is incorrect
+		// The correct endpoint for global is "aiplatform.googleapis.com"
+		const baseURL = region === "global" ? `https://aiplatform.googleapis.com/v1` : undefined // Let the SDK use its default for other regions
+
 		if (this.options.vertexJsonCredentials) {
 			this.client = new AnthropicVertex({
 				projectId,
 				region,
+				baseURL,
 				googleAuth: new GoogleAuth({
 					scopes: ["https://www.googleapis.com/auth/cloud-platform"],
 					credentials: safeJsonParse<JWTInput>(this.options.vertexJsonCredentials, undefined),
@@ -47,13 +53,14 @@ export class AnthropicVertexHandler extends BaseProvider implements SingleComple
 			this.client = new AnthropicVertex({
 				projectId,
 				region,
+				baseURL,
 				googleAuth: new GoogleAuth({
 					scopes: ["https://www.googleapis.com/auth/cloud-platform"],
 					keyFile: this.options.vertexKeyFile,
 				}),
 			})
 		} else {
-			this.client = new AnthropicVertex({ projectId, region })
+			this.client = new AnthropicVertex({ projectId, region, baseURL })
 		}
 	}