diff --git a/packages/core/auth-js/src/lib/types.ts b/packages/core/auth-js/src/lib/types.ts
index 5a2327d6..930d994f 100644
--- a/packages/core/auth-js/src/lib/types.ts
+++ b/packages/core/auth-js/src/lib/types.ts
@@ -1439,7 +1439,31 @@ export type RequiredClaims = {
   session_id: string
 }
 
-export type JwtPayload = RequiredClaims & {
+/**
+ * JWT Payload containing claims for Supabase authentication tokens.
+ *
+ * Required claims (iss, aud, exp, iat, sub, role, aal, session_id) are inherited from RequiredClaims.
+ * All other claims are optional as they can be customized via Custom Access Token Hooks.
+ *
+ * @see https://supabase.com/docs/guides/auth/jwt-fields
+ */
+export interface JwtPayload extends RequiredClaims {
+  // Standard optional claims (can be customized via custom access token hooks)
+  email?: string
+  phone?: string
+  is_anonymous?: boolean
+
+  // Optional claims
+  jti?: string
+  nbf?: number
+  app_metadata?: UserAppMetadata
+  user_metadata?: UserMetadata
+  amr?: AMREntry[]
+
+  // Special claims (only in anon/service role tokens)
+  ref?: string
+
+  // Allow custom claims via custom access token hooks
   [key: string]: any
 }
 
diff --git a/packages/core/auth-js/test/GoTrueClient.test.ts b/packages/core/auth-js/test/GoTrueClient.test.ts
index 5ed3fd4f..d5141511 100644
--- a/packages/core/auth-js/test/GoTrueClient.test.ts
+++ b/packages/core/auth-js/test/GoTrueClient.test.ts
@@ -1613,6 +1613,87 @@ describe('getClaims', () => {
     expect(authWithSession.getUser).toHaveBeenCalled()
   })
 
+  test('getClaims returns properly typed JwtPayload with documented fields', async () => {
+    const { email, password } = mockUserCredentials()
+    const {
+      data: { user },
+      error: initialError,
+    } = await authWithSession.signUp({
+      email,
+      password,
+    })
+    expect(initialError).toBeNull()
+    expect(user).not.toBeNull()
+
+    const { data, error } = await authWithSession.getClaims()
+    expect(error).toBeNull()
+    expect(data).not.toBeNull()
+
+    const claims = data?.claims
+    expect(claims).toBeDefined()
+
+    // Test core required claims that are always present
+    expect(typeof claims?.sub).toBe('string')
+    expect(typeof claims?.role).toBe('string')
+
+    // Test standard optional claims
+    if (claims?.email !== undefined) {
+      expect(typeof claims.email).toBe('string')
+    }
+    if (claims?.phone !== undefined) {
+      expect(typeof claims.phone).toBe('string')
+    }
+    if (claims?.user_metadata !== undefined) {
+      expect(typeof claims.user_metadata).toBe('object')
+    }
+    if (claims?.app_metadata !== undefined) {
+      expect(typeof claims.app_metadata).toBe('object')
+    }
+    if (claims?.is_anonymous !== undefined) {
+      expect(typeof claims.is_anonymous).toBe('boolean')
+    }
+
+    // Test optional JWT standard claims if present
+    if (claims?.iss !== undefined) {
+      expect(typeof claims.iss).toBe('string')
+    }
+    if (claims?.aud !== undefined) {
+      expect(['string', 'object']).toContain(typeof claims.aud)
+    }
+    if (claims?.exp !== undefined) {
+      expect(typeof claims.exp).toBe('number')
+    }
+    if (claims?.iat !== undefined) {
+      expect(typeof claims.iat).toBe('number')
+    }
+    if (claims?.aal !== undefined) {
+      expect(typeof claims.aal).toBe('string')
+    }
+    if (claims?.session_id !== undefined) {
+      expect(typeof claims.session_id).toBe('string')
+    }
+    if (claims?.jti !== undefined) {
+      expect(typeof claims.jti).toBe('string')
+    }
+    if (claims?.nbf !== undefined) {
+      expect(typeof claims.nbf).toBe('number')
+    }
+
+    // Verify amr array structure if present
+    if (claims?.amr) {
+      expect(Array.isArray(claims.amr)).toBe(true)
+      if (claims.amr.length > 0) {
+        expect(typeof claims.amr[0].method).toBe('string')
+        expect(typeof claims.amr[0].timestamp).toBe('number')
+      }
+    }
+
+    // Verify ref claim if present (anon/service role tokens)
+    if (claims?.ref !== undefined) {
+      expect(typeof claims.ref).toBe('string')
+    }
+  })
+
   test('getClaims fetches JWKS to verify asymmetric jwt', async () => {
     const fetchedUrls: any[] = []
     const fetchedResponse: any[] = []