diff --git a/packages/react-bindings/src/__tests__/useStatsigInternalClientFactoryBootstrap.test.tsx b/packages/react-bindings/src/__tests__/useStatsigInternalClientFactoryBootstrap.test.tsx
new file mode 100644
index 00000000..c0e39414
--- /dev/null
+++ b/packages/react-bindings/src/__tests__/useStatsigInternalClientFactoryBootstrap.test.tsx
@@ -0,0 +1,145 @@
+import '@testing-library/jest-dom';
+import { render } from '@testing-library/react';
+import * as React from 'react';
+import { MockRemoteServerEvalClient } from 'statsig-test-helpers';
+
+import { _getStatsigGlobal } from '@statsig/client-core';
+
+import { useStatsigInternalClientFactoryBootstrap } from '../useStatsigInternalClientFactoryBootstrap';
+
+function clientFactory() {
+  const client = MockRemoteServerEvalClient.create();
+
+  // Add dataAdapter mock with both setData and setDataLegacy methods
+  client.dataAdapter = {
+    setData: jest.fn(),
+    setDataLegacy: jest.fn(),
+  };
+
+  let resolveinitializeAsync: (() => void) | undefined;
+  client.initializeAsync.mockReturnValue(
+    new Promise<void>((resolve) => {
+      resolveinitializeAsync = resolve;
+    }),
+  );
+  return {
+    client,
+    finishInitializeAsync: () => {
+      resolveinitializeAsync?.();
+    },
+  };
+}
+
+const TestComponent = ({
+  sdkKey,
+  useLegacyClient,
+  onClientCreated,
+}: {
+  sdkKey: string;
+  useLegacyClient?: boolean;
+  onClientCreated?: (client: any) => void;
+}) => {
+  const client = useStatsigInternalClientFactoryBootstrap(
+    (_args) => {
+      const { client } = clientFactory();
+      onClientCreated?.(client);
+      return client;
+    },
+    {
+      sdkKey,
+      initialUser: { userID: 'test-user' },
+      initialValues: JSON.stringify({ test: 'data' }),
+      statsigOptions: null,
+      useLegacyClient,
+    },
+  );
+
+  return <div data-testid="client-ready">{client ? 'Ready' : 'Not Ready'}</div>;
+};
+
+describe('useStatsigInternalClientFactoryBootstrap', () => {
+  const readySdkKey = 'client-key-ready';
+
+  beforeAll(() => {
+    // Create mock SDK that's ready
+    const { client } = clientFactory();
+    (client.loadingStatus as any) = 'Ready';
+
+    // Add this client to Statsig Global with the sdkKey
+    const global = _getStatsigGlobal();
+    const instances = global.instances ?? {};
+    instances[readySdkKey] = client;
+    global.instances = instances;
+  });
+
+  afterAll(() => {
+    delete _getStatsigGlobal().instances;
+  });
+
+  beforeEach(() => {
+    jest.clearAllMocks();
+  });
+
+  it('calls setData when useLegacyClient is false', () => {
+    let capturedClient: any = null;
+
+    render(
+      <TestComponent
+        sdkKey="test-sdk-key-standard"
+        useLegacyClient={false}
+        onClientCreated={(client) => {
+          capturedClient = client;
+        }}
+      />,
+    );
+
+    expect(capturedClient).not.toBeNull();
+    expect(capturedClient.dataAdapter.setData).toHaveBeenCalledWith(
+      JSON.stringify({ test: 'data' }),
+    );
+    expect(capturedClient.dataAdapter.setDataLegacy).not.toHaveBeenCalled();
+    expect(capturedClient.initializeSync).toHaveBeenCalled();
+  });
+
+  it('calls setData when useLegacyClient is not provided (default behavior)', () => {
+    let capturedClient: any = null;
+
+    render(
+      <TestComponent
+        sdkKey="test-sdk-key-default"
+        onClientCreated={(client) => {
+          capturedClient = client;
+        }}
+      />,
+    );
+
+    expect(capturedClient).not.toBeNull();
+    expect(capturedClient.dataAdapter.setData).toHaveBeenCalledWith(
+      JSON.stringify({ test: 'data' }),
+    );
+    expect(capturedClient.dataAdapter.setDataLegacy).not.toHaveBeenCalled();
+    expect(capturedClient.initializeSync).toHaveBeenCalled();
+  });
+
+  it('calls setDataLegacy when useLegacyClient is true', () => {
+    let capturedClient: any = null;
+
+    render(
+      <TestComponent
+        sdkKey="test-sdk-key-legacy"
+        useLegacyClient={true}
+        onClientCreated={(client) => {
+          capturedClient = client;
+        }}
+      />,
+    );
+
+    expect(capturedClient).not.toBeNull();
+    expect(capturedClient.dataAdapter.setDataLegacy).toHaveBeenCalledWith(
+      JSON.stringify({ test: 'data' }),
+      { userID: 'test-user' },
+    );
+    expect(capturedClient.dataAdapter.setData).not.toHaveBeenCalled();
+    expect(capturedClient.initializeSync).toHaveBeenCalled();
+  });
+});
diff --git a/packages/react-bindings/src/useClientBootstrapInit.ts b/packages/react-bindings/src/useClientBootstrapInit.ts
index 50864cd6..edc4250e 100644
--- a/packages/react-bindings/src/useClientBootstrapInit.ts
+++ b/packages/react-bindings/src/useClientBootstrapInit.ts
@@ -8,6 +8,7 @@ export function useClientBootstrapInit(
   initialUser: StatsigUser,
   initialValues: string,
   statsigOptions: StatsigOptions | null = null,
+  useLegacyClient?: boolean,
 ): StatsigClient {
   return useStatsigInternalClientFactoryBootstrap(
     (args) =>
@@ -17,6 +18,7 @@ export function useClientBootstrapInit(
       initialUser,
       initialValues,
       statsigOptions,
+      useLegacyClient,
     },
   );
 }
diff --git a/packages/react-bindings/src/useStatsigInternalClientFactoryBootstrap.ts b/packages/react-bindings/src/useStatsigInternalClientFactoryBootstrap.ts
index 69980d8c..32bb7542 100644
--- a/packages/react-bindings/src/useStatsigInternalClientFactoryBootstrap.ts
+++ b/packages/react-bindings/src/useStatsigInternalClientFactoryBootstrap.ts
@@ -8,6 +8,7 @@ type FactoryArgs = {
   initialUser: StatsigUser;
   initialValues: string;
   statsigOptions: StatsigOptions | null;
+  useLegacyClient?: boolean;
 };
 
 export function useStatsigInternalClientFactoryBootstrap<
@@ -23,7 +24,12 @@ export function useStatsigInternalClientFactoryBootstrap<
     const inst = factory(args);
     clientRef.current = inst;
 
-    inst.dataAdapter.setData(args.initialValues);
+    if (args.useLegacyClient) {
+      inst.dataAdapter.setDataLegacy(args.initialValues, args.initialUser);
+    } else {
+      inst.dataAdapter.setData(args.initialValues);
+    }
+
     inst.initializeSync();
 
     return inst;