diff --git a/apps/cli/src/tui/components/dialogs/provider-picker.tsx b/apps/cli/src/tui/components/dialogs/provider-picker.tsx
index af5d02bac2..179f2f4ee4 100644
--- a/apps/cli/src/tui/components/dialogs/provider-picker.tsx
+++ b/apps/cli/src/tui/components/dialogs/provider-picker.tsx
@@ -27,6 +27,7 @@ import {
 	getDefaultAwsRegion,
 	type ProviderConfigValues,
 	resolveProviderConfigAwsRegion,
+	resolveProviderConfigGcp,
 	resolveProviderConfigSap,
 	updateProviderConfigValue,
 } from "../../utils/provider-config-values";
@@ -317,6 +318,8 @@ const DEFAULT_FIELD_LABELS: Partial<Record<ProviderConfigFieldKey, string>> = {
 	baseUrl: "Base URL",
 	awsRegion: "AWS Region",
 	awsProfile: "AWS Profile Name",
+	gcpProjectId: "Google Cloud Project ID",
+	gcpRegion: "Google Cloud Region",
 	sapClientId: "Client ID",
 	sapClientSecret: "Client Secret",
 	sapTokenUrl: "Token URL",
@@ -331,6 +334,8 @@ const DEFAULT_FIELD_PLACEHOLDERS: Partial<
 	baseUrl: "",
 	awsRegion: "us-east-1",
 	awsProfile: "default",
+	gcpProjectId: "my-gcp-project",
+	gcpRegion: "us-central1",
 	sapClientId: "sb-...|xsuaa_std!b...",
 	sapClientSecret: "SAP AI Core client secret",
 	sapTokenUrl: "https://<subdomain>.authentication.sap.hana.ondemand.com",
@@ -341,6 +346,8 @@ const DEFAULT_FIELD_PLACEHOLDERS: Partial<
 /** Render order for cycling focus with Tab. */
 const FIELD_ORDER: ProviderConfigFieldKey[] = [
 	"awsRegion",
+	"gcpProjectId",
+	"gcpRegion",
 	"baseUrl",
 	"apiKey",
 	"awsProfile",
@@ -403,6 +410,13 @@ export function ProviderConfigInputContent(
 			initial.awsRegion =
 				existingSettings?.aws?.region?.trim() || getDefaultAwsRegion(ep);
 		}
+		if (config.fields.gcpProjectId)
+			initial.gcpProjectId = existingSettings?.gcp?.projectId?.trim() ?? "";
+		if (config.fields.gcpRegion)
+			initial.gcpRegion =
+				existingSettings?.gcp?.region?.trim() ??
+				config.fields.gcpRegion.defaultValue ??
+				"us-central1";
 		if (config.fields.apiKey)
 			initial.apiKey = existingSettings?.apiKey?.trim() ?? "";
 		if (config.fields.awsProfile)
@@ -431,6 +445,7 @@ export function ProviderConfigInputContent(
 		const apiKey = values.apiKey?.trim();
 		const awsProfile = values.awsProfile?.trim();
 		const hasAwsFields = config.fields.awsRegion || config.fields.awsProfile;
+		const hasGcpFields = config.fields.gcpProjectId || config.fields.gcpRegion;
 		const hasSapFields =
 			config.fields.sapClientId ||
 			config.fields.sapClientSecret ||
@@ -448,6 +463,7 @@ export function ProviderConfigInputContent(
 						profile: apiKey ? undefined : awsProfile || undefined,
 					}
 				: undefined,
+			gcp: hasGcpFields ? resolveProviderConfigGcp(values) : undefined,
 			sap: hasSapFields ? resolveProviderConfigSap(values) : undefined,
 		});
 		resolve(true);
diff --git a/apps/cli/src/tui/utils/provider-config-values.test.ts b/apps/cli/src/tui/utils/provider-config-values.test.ts
index 92b75f69c7..1be10ee330 100644
--- a/apps/cli/src/tui/utils/provider-config-values.test.ts
+++ b/apps/cli/src/tui/utils/provider-config-values.test.ts
@@ -5,6 +5,7 @@ import { afterEach, describe, expect, it } from "vitest";
 import {
 	getDefaultAwsRegion,
 	resolveProviderConfigAwsRegion,
+	resolveProviderConfigGcp,
 	resolveProviderConfigSap,
 	updateProviderConfigValue,
 } from "./provider-config-values";
@@ -66,6 +67,16 @@ describe("provider config values", () => {
 		).toBe("us-west-2");
 	});
 
+	it("resolves Vertex GCP field values into GCP settings", () => {
+		expect(resolveProviderConfigGcp({ gcpRegion: "us-central1" })).toBeUndefined();
+		expect(
+			resolveProviderConfigGcp({
+				gcpProjectId: " project ",
+				gcpRegion: " europe-west4 ",
+			}),
+		).toEqual({ projectId: "project", region: "europe-west4" });
+	});
+
 	it("resolves SAP AI Core field values into SAP settings", () => {
 		expect(
 			resolveProviderConfigSap({
diff --git a/apps/cli/src/tui/utils/provider-config-values.ts b/apps/cli/src/tui/utils/provider-config-values.ts
index e78a089e11..7c1f9fc374 100644
--- a/apps/cli/src/tui/utils/provider-config-values.ts
+++ b/apps/cli/src/tui/utils/provider-config-values.ts
@@ -6,6 +6,7 @@ export type ProviderConfigValues = Partial<
 >;
 
 const DEFAULT_AWS_REGION = "us-east-1";
+const DEFAULT_GCP_REGION = "us-central1";
 
 export function getDefaultAwsRegion(profile?: string): string {
 	return (
@@ -20,6 +21,20 @@ export function resolveProviderConfigAwsRegion(
 	return values.awsRegion?.trim() || getDefaultAwsRegion(values.awsProfile);
 }
 
+export function resolveProviderConfigGcp(values: ProviderConfigValues):
+	| {
+			projectId?: string;
+			region?: string;
+	  }
+	| undefined {
+	const projectId = values.gcpProjectId?.trim() || undefined;
+	if (!projectId) return undefined;
+	return {
+		projectId,
+		region: values.gcpRegion?.trim() || DEFAULT_GCP_REGION,
+	};
+}
+
 export function resolveProviderConfigSap(values: ProviderConfigValues):
 	| {
 			clientId?: string;
diff --git a/apps/cli/src/utils/provider-readiness.test.ts b/apps/cli/src/utils/provider-readiness.test.ts
index 6536b5c969..d794e7f931 100644
--- a/apps/cli/src/utils/provider-readiness.test.ts
+++ b/apps/cli/src/utils/provider-readiness.test.ts
@@ -139,6 +139,12 @@ describe("provider readiness", () => {
 				gcp: { projectId: "test-project" },
 			} satisfies ProviderSettings),
 		).toBe(true);
+		expect(
+			isProviderSettingsUsable("vertex", {
+				provider: "vertex",
+				gcp: { projectId: "test-project", region: "us-central1" },
+			} satisfies ProviderSettings),
+		).toBe(true);
 		expect(
 			isProviderSettingsUsable("sapaicore", {
 				provider: "sapaicore",
diff --git a/apps/cli/src/utils/provider-readiness.ts b/apps/cli/src/utils/provider-readiness.ts
index d804419068..c99fd85551 100644
--- a/apps/cli/src/utils/provider-readiness.ts
+++ b/apps/cli/src/utils/provider-readiness.ts
@@ -33,6 +33,8 @@ function hasAwsRegion(settings: ProviderSettings): boolean {
 
 function hasGcpCredentials(settings: ProviderSettings): boolean {
 	const gcp = settings.gcp;
+	// Vertex defaults to us-central1 at runtime when no region is stored, so keep
+	// existing project-only configs usable while new CLI saves include a region.
 	return hasText(gcp?.projectId);
 }
 
diff --git a/sdk/packages/core/src/services/local-runtime-bootstrap.ts b/sdk/packages/core/src/services/local-runtime-bootstrap.ts
index 3dbb5e4197..ef313fee2f 100644
--- a/sdk/packages/core/src/services/local-runtime-bootstrap.ts
+++ b/sdk/packages/core/src/services/local-runtime-bootstrap.ts
@@ -189,6 +189,7 @@ function buildProviderConfig(
 					...(stored?.modelCatalog ?? {}),
 				}
 			: undefined;
+	const sessionProviderConfig = config.providerConfig?.providerId === config.providerId ? config.providerConfig : undefined;
 	const settings: ProviderSettings = {
 		...(stored ?? {}),
 		provider: config.providerId,
@@ -209,7 +210,10 @@ function buildProviderConfig(
 		reasoning: resolveReasoningSettings(config, stored?.reasoning),
 		modelCatalog,
 	};
-	const providerConfig = toProviderConfig(settings);
+	const providerConfig: ProviderConfig = {
+		...toProviderConfig(settings),
+		...(sessionProviderConfig ?? {}),
+	};
 	if (config.knownModels) {
 		providerConfig.knownModels = config.knownModels;
 	}
diff --git a/sdk/packages/core/src/services/providers/provider-config-fields.test.ts b/sdk/packages/core/src/services/providers/provider-config-fields.test.ts
index a4cb014a2c..7149a57110 100644
--- a/sdk/packages/core/src/services/providers/provider-config-fields.test.ts
+++ b/sdk/packages/core/src/services/providers/provider-config-fields.test.ts
@@ -94,6 +94,21 @@ describe("getProviderConfigFields", () => {
 		);
 	});
 
+	it("returns Vertex GCP config fields with optional API key", () => {
+		const result = getProviderConfigFields("vertex");
+		expect(result.providerId).toBe("vertex");
+		expect(result.authMethod).toBe("api-key");
+		expect(result.description).toMatch(/Application Default Credentials/i);
+		expect(Object.keys(result.fields)).toEqual([
+			"gcpProjectId",
+			"gcpRegion",
+			"apiKey",
+		]);
+		expect(result.fields.gcpProjectId?.label).toBe("Google Cloud Project ID");
+		expect(result.fields.gcpRegion?.defaultValue).toBe("us-central1");
+		expect(result.fields.apiKey?.optional).toBe(true);
+	});
+
 	it("returns api-key auth with awsRegion, apiKey, and awsProfile for bedrock", () => {
 		const result = getProviderConfigFields("bedrock");
 		expect(result.providerId).toBe("bedrock");
diff --git a/sdk/packages/core/src/services/providers/provider-config-fields.ts b/sdk/packages/core/src/services/providers/provider-config-fields.ts
index 8a69cec32b..80dc01535b 100644
--- a/sdk/packages/core/src/services/providers/provider-config-fields.ts
+++ b/sdk/packages/core/src/services/providers/provider-config-fields.ts
@@ -6,6 +6,8 @@ export type ProviderConfigFieldKey =
 	| "baseUrl"
 	| "awsRegion"
 	| "awsProfile"
+	| "gcpProjectId"
+	| "gcpRegion"
 	| "sapClientId"
 	| "sapClientSecret"
 	| "sapTokenUrl"
@@ -35,6 +37,8 @@ const FIELD_KEYS: ProviderConfigFieldKey[] = [
 	"baseUrl",
 	"awsRegion",
 	"awsProfile",
+	"gcpProjectId",
+	"gcpRegion",
 	"sapClientId",
 	"sapClientSecret",
 	"sapTokenUrl",
@@ -53,6 +57,27 @@ interface ProviderConfigFieldMetadata {
 const PROVIDER_CONFIG_FIELD_METADATA: Partial<
 	Record<string, ProviderConfigFieldMetadata>
 > = {
+	vertex: {
+		mode: "replace",
+		description:
+			"Vertex AI can use Google Cloud Application Default Credentials with a project/region. An API key is optional for supported Gemini models.",
+		fields: {
+			gcpProjectId: {
+				label: "Google Cloud Project ID",
+				placeholder: "my-gcp-project",
+			},
+			gcpRegion: {
+				label: "Google Cloud Region",
+				placeholder: "us-central1",
+				defaultValue: "us-central1",
+			},
+			apiKey: {
+				label: "API Key (optional)",
+				placeholder: "Leave blank to use Google Cloud credentials",
+				optional: true,
+			},
+		},
+	},
 	bedrock: {
 		mode: "replace",
 		description:
diff --git a/sdk/packages/llms/src/providers/vendors/vertex.test.ts b/sdk/packages/llms/src/providers/vendors/vertex.test.ts
index 78c5373ef8..f6a19bc381 100644
--- a/sdk/packages/llms/src/providers/vendors/vertex.test.ts
+++ b/sdk/packages/llms/src/providers/vendors/vertex.test.ts
@@ -60,6 +60,30 @@ describe("createVertexProviderModule", () => {
 		expect(createVertexAnthropicMock).not.toHaveBeenCalled();
 	});
 
+	it("accepts nested gcp project and region options", async () => {
+		await createVertexProviderModule(
+			config({
+				options: {
+					gcp: {
+						projectId: "nested-project",
+						region: "europe-west4",
+					},
+				},
+			}),
+			context("gemini-3-flash-preview"),
+		);
+
+		expect(createVertexMock).toHaveBeenCalledWith(
+			expect.objectContaining({
+				project: "nested-project",
+				location: "europe-west4",
+				googleAuthOptions: {
+					projectId: "nested-project",
+				},
+			}),
+		);
+	});
+
 	it("keeps API-key express mode when Gemini config has no GCP settings", async () => {
 		await createVertexProviderModule(
 			config({
diff --git a/sdk/packages/llms/src/providers/vendors/vertex.ts b/sdk/packages/llms/src/providers/vendors/vertex.ts
index 2a5d5cadeb..d6df1ddc94 100644
--- a/sdk/packages/llms/src/providers/vendors/vertex.ts
+++ b/sdk/packages/llms/src/providers/vendors/vertex.ts
@@ -8,22 +8,35 @@ import { ensureFetch, resolveApiKey } from "../http";
 import { isClaudeModelId } from "../model-facts";
 import type { ProviderFactoryResult } from "./types";
 
+function readStringOption(options: Record<string, unknown> | undefined, key: string): string | undefined {
+	const value = options?.[key];
+	return typeof value === "string" && value.trim().length > 0 ? value : undefined;
+}
+
+function readNestedStringOption(options: Record<string, unknown> | undefined, objectKey: string, key: string): string | undefined {
+	const object = options?.[objectKey];
+	if (!object || typeof object !== "object" || Array.isArray(object)) {
+		return undefined;
+	}
+	const value = (object as Record<string, unknown>)[key];
+	return typeof value === "string" && value.trim().length > 0 ? value : undefined;
+}
+
 export async function createVertexProviderModule(
 	config: GatewayResolvedProviderConfig,
 	context: GatewayProviderContext,
 ): Promise<ProviderFactoryResult> {
-	const project = String(
-		config.options?.project ?? config.options?.projectId ?? "",
-	);
-	const location = String(
-		config.options?.location ?? config.options?.region ?? "us-central1",
-	);
-	const googleAuthProjectId =
-		typeof config.options?.project === "string"
-			? config.options.project
-			: typeof config.options?.projectId === "string"
-				? config.options.projectId
-				: undefined;
+	const project =
+		readStringOption(config.options, "project") ??
+		readStringOption(config.options, "projectId") ??
+		readNestedStringOption(config.options, "gcp", "projectId") ??
+		"";
+	const location =
+		readStringOption(config.options, "location") ??
+		readStringOption(config.options, "region") ??
+		readNestedStringOption(config.options, "gcp", "region") ??
+		"us-central1";
+	const googleAuthProjectId = project || undefined;
 	const fetch = ensureFetch(config.fetch);
 
 	if (isClaudeModelId(context.model.id)) {