diff --git a/.changeset/major-parks-study.md b/.changeset/major-parks-study.md
new file mode 100644
index 00000000000..55bf83977a6
--- /dev/null
+++ b/.changeset/major-parks-study.md
@@ -0,0 +1,5 @@
+---
+"@clerk/clerk-js": patch
+---
+
+Support both `clerkUICtor` and `clerkUiCtor` option names for backwards compatibility
diff --git a/packages/clerk-js/src/core/__tests__/clerk.test.ts b/packages/clerk-js/src/core/__tests__/clerk.test.ts
index ab27b1d1646..f46c3a4686e 100644
--- a/packages/clerk-js/src/core/__tests__/clerk.test.ts
+++ b/packages/clerk-js/src/core/__tests__/clerk.test.ts
@@ -2732,4 +2732,69 @@ describe('Clerk singleton', () => {
       });
     });
   });
+
+  describe('clerkUICtor backwards compatibility', () => {
+    beforeEach(() => {
+      mockEnvironmentFetch.mockReturnValue(
+        Promise.resolve({
+          userSettings: mockUserSettings,
+          displayConfig: mockDisplayConfig,
+          isSingleSession: () => false,
+          isProduction: () => true,
+          isDevelopmentOrStaging: () => false,
+        }),
+      );
+      mockClientFetch.mockReturnValue(
+        Promise.resolve({
+          signedInSessions: [],
+        }),
+      );
+    });
+
+    it('uses clerkUICtor when provided with correct casing', async () => {
+      const mockClerkUIInstance = { mount: vi.fn() };
+      const mockClerkUICtor = vi.fn(() => mockClerkUIInstance);
+
+      const sut = new Clerk(productionPublishableKey);
+      await sut.load({
+        ...mockedLoadOptions,
+        clerkUICtor: mockClerkUICtor,
+      });
+
+      expect(mockClerkUICtor).toHaveBeenCalled();
+    });
+
+    it('uses clerkUiCtor (legacy casing) for backwards compatibility', async () => {
+      const mockClerkUIInstance = { mount: vi.fn() };
+      const mockClerkUICtor = vi.fn(() => mockClerkUIInstance);
+
+      const sut = new Clerk(productionPublishableKey);
+      // Use legacy casing - cast to bypass TypeScript since clerkUiCtor is not in the type
+      await sut.load({
+        ...mockedLoadOptions,
+        clerkUiCtor: mockClerkUICtor,
+      } as Parameters<typeof sut.load>[0]);
+
+      expect(mockClerkUICtor).toHaveBeenCalled();
+    });
+
+    it('prefers clerkUICtor over clerkUiCtor when both are provided', async () => {
+      const mockClerkUIInstanceCorrect = { mount: vi.fn() };
+      const mockClerkUICtorCorrect = vi.fn(() => mockClerkUIInstanceCorrect);
+
+      const mockClerkUIInstanceLegacy = { mount: vi.fn() };
+      const mockClerkUICtorLegacy = vi.fn(() => mockClerkUIInstanceLegacy);
+
+      const sut = new Clerk(productionPublishableKey);
+      // Provide both - the correct casing should take precedence
+      await sut.load({
+        ...mockedLoadOptions,
+        clerkUICtor: mockClerkUICtorCorrect,
+        clerkUiCtor: mockClerkUICtorLegacy,
+      } as Parameters<typeof sut.load>[0]);
+
+      expect(mockClerkUICtorCorrect).toHaveBeenCalled();
+      expect(mockClerkUICtorLegacy).not.toHaveBeenCalled();
+    });
+  });
 });
diff --git a/packages/clerk-js/src/core/clerk.ts b/packages/clerk-js/src/core/clerk.ts
index 01395bac1b4..52ad8d2a7df 100644
--- a/packages/clerk-js/src/core/clerk.ts
+++ b/packages/clerk-js/src/core/clerk.ts
@@ -3248,9 +3248,14 @@ export class Clerk implements ClerkInterface {
   };
 
   #initOptions = (options?: ClerkOptions): ClerkOptions => {
+    // Support both clerkUICtor (correct) and clerkUiCtor (legacy) for backwards compatibility
+    const clerkUICtor =
+      options?.clerkUICtor ?? (options as Record<string, unknown> | undefined)?.clerkUiCtor ?? undefined;
+
     return {
       ...defaultOptions,
       ...options,
+      clerkUICtor: clerkUICtor as ClerkOptions['clerkUICtor'],
       allowedRedirectOrigins: createAllowedRedirectOrigins(
         options?.allowedRedirectOrigins,
         this.frontendApi,