diff --git a/ui/litellm-dashboard/src/app/onboarding/OnboardingForm.test.tsx b/ui/litellm-dashboard/src/app/onboarding/OnboardingForm.test.tsx
index 965b0db47c3..d40fc82be07 100644
--- a/ui/litellm-dashboard/src/app/onboarding/OnboardingForm.test.tsx
+++ b/ui/litellm-dashboard/src/app/onboarding/OnboardingForm.test.tsx
@@ -5,17 +5,14 @@ import { OnboardingForm } from "./OnboardingForm";
 
 const mockUseOnboardingCredentials = vi.fn();
 const mockClaimToken = vi.fn();
+const mockJwtDecode = vi.fn();
 
 vi.mock("next/navigation", () => ({
   useSearchParams: () => new URLSearchParams("invitation_id=inv-123"),
 }));
 
 vi.mock("jwt-decode", () => ({
-  jwtDecode: vi.fn(() => ({
-    user_email: "alice@example.com",
-    user_id: "user-1",
-    key: "access-tok",
-  })),
+  jwtDecode: (...args: unknown[]) => mockJwtDecode(...args),
 }));
 
 vi.mock("@/app/(dashboard)/hooks/onboarding/useOnboarding", () => ({
@@ -23,8 +20,14 @@ vi.mock("@/app/(dashboard)/hooks/onboarding/useOnboarding", () => ({
   useClaimOnboardingToken: () => ({ mutate: mockClaimToken, isPending: false }),
 }));
 
+let currentAuthHeaderName = "Authorization";
+
 vi.mock("@/components/networking", () => ({
   getProxyBaseUrl: vi.fn(() => ""),
+  setGlobalLitellmHeaderName: (headerName: string) => {
+    currentAuthHeaderName = headerName;
+  },
+  getGlobalLitellmHeaderName: () => currentAuthHeaderName,
 }));
 
 vi.mock("./OnboardingLoadingView", () => ({
@@ -60,6 +63,12 @@ vi.mock("./OnboardingFormBody", () => ({
 describe("OnboardingForm", () => {
   beforeEach(() => {
     vi.clearAllMocks();
+    currentAuthHeaderName = "Authorization";
+    mockJwtDecode.mockReturnValue({
+      user_email: "alice@example.com",
+      user_id: "user-1",
+      key: "access-tok",
+    });
     document.cookie = "token=; expires=Thu, 01 Jan 1970 00:00:00 GMT; path=/";
     document.cookie = "token=; expires=Thu, 01 Jan 1970 00:00:00 GMT; path=/ui";
     sessionStorage.clear();
@@ -166,6 +175,62 @@ describe("OnboardingForm", () => {
     cookieSpy.mockRestore();
   });
 
+  it("should send the claim request with the proxy's custom auth header name", async () => {
+    mockJwtDecode.mockReturnValue({
+      user_email: "alice@example.com",
+      user_id: "user-1",
+      key: "access-tok",
+      auth_header_name: "x-litellm-api-key",
+    });
+    mockUseOnboardingCredentials.mockReturnValue({
+      data: { token: "fake-jwt-token" },
+      isLoading: false,
+      isError: false,
+    });
+
+    // The onboarding page has no session yet, so the only source for a custom
+    // `litellm_key_header_name` is the onboarding token's own claims; without
+    // propagating it the claim lands in `Authorization` and the proxy answers
+    // "Missing onboarding session for invitation link."
+    const { getGlobalLitellmHeaderName } = await import("@/components/networking");
+    const headerNameAtClaimTime: string[] = [];
+    mockClaimToken.mockImplementation((_params, options) => {
+      headerNameAtClaimTime.push(getGlobalLitellmHeaderName());
+      options.onSuccess({ token: "NEW_USER_TOKEN" });
+    });
+
+    render(<OnboardingForm variant="signup" />);
+
+    await act(async () => {
+      fireEvent.click(screen.getByRole("button", { name: "Submit" }));
+    });
+
+    expect(headerNameAtClaimTime).toEqual(["x-litellm-api-key"]);
+  });
+
+  it("should keep the default auth header name when the onboarding token has no custom header claim", async () => {
+    mockUseOnboardingCredentials.mockReturnValue({
+      data: { token: "fake-jwt-token" },
+      isLoading: false,
+      isError: false,
+    });
+
+    const { getGlobalLitellmHeaderName } = await import("@/components/networking");
+    const headerNameAtClaimTime: string[] = [];
+    mockClaimToken.mockImplementation((_params, options) => {
+      headerNameAtClaimTime.push(getGlobalLitellmHeaderName());
+      options.onSuccess({ token: "NEW_USER_TOKEN" });
+    });
+
+    render(<OnboardingForm variant="signup" />);
+
+    await act(async () => {
+      fireEvent.click(screen.getByRole("button", { name: "Submit" }));
+    });
+
+    expect(headerNameAtClaimTime).toEqual(["Authorization"]);
+  });
+
   it("should show claim error when claim response is missing final token", async () => {
     mockUseOnboardingCredentials.mockReturnValue({
       data: { token: "fake-jwt-token" },
diff --git a/ui/litellm-dashboard/src/app/onboarding/OnboardingForm.tsx b/ui/litellm-dashboard/src/app/onboarding/OnboardingForm.tsx
index 23a8bc6725a..54d2711ce5e 100644
--- a/ui/litellm-dashboard/src/app/onboarding/OnboardingForm.tsx
+++ b/ui/litellm-dashboard/src/app/onboarding/OnboardingForm.tsx
@@ -3,7 +3,7 @@ import React from "react";
 import { useSearchParams } from "next/navigation";
 import { jwtDecode } from "jwt-decode";
 import { useOnboardingCredentials, useClaimOnboardingToken } from "@/app/(dashboard)/hooks/onboarding/useOnboarding";
-import { getProxyBaseUrl } from "@/components/networking";
+import { getProxyBaseUrl, setGlobalLitellmHeaderName } from "@/components/networking";
 import { clearTokenCookies, storeLoginToken } from "@/utils/cookieUtils";
 import { OnboardingLoadingView } from "./OnboardingLoadingView";
 import { OnboardingErrorView } from "./OnboardingErrorView";
@@ -30,12 +30,17 @@ export function OnboardingForm({ variant }: OnboardingFormProps) {
   const userEmail: string = decoded?.user_email ?? "";
   const userId: string | null = decoded?.user_id ?? null;
   const accessToken: string | null = decoded?.key ?? null;
+  const authHeaderName: string | null = decoded?.auth_header_name ?? null;
 
   const handleSubmit = (formValues: { password: string }) => {
     if (!accessToken || !userId || !inviteId) return;
 
     setClaimError(null);
 
+    if (authHeaderName) {
+      setGlobalLitellmHeaderName(authHeaderName);
+    }
+
     claimToken(
       { accessToken, inviteId, userId, password: formValues.password },
       {