diff --git a/src/shared/components/Modal.tsx b/src/shared/components/Modal.tsx
index 74d0043a77d1..503c22a81fb3 100644
--- a/src/shared/components/Modal.tsx
+++ b/src/shared/components/Modal.tsx
@@ -60,12 +60,18 @@ const TOASTER_SELECTOR = '[data-slot="toaster"]';
 const isFromToaster = (event: Event) =>
   event.target instanceof Element && event.target.closest(TOASTER_SELECTOR) !== null;
 
+// Dialogs take ~70% of the viewport from the `sm` breakpoint up, so settings-style modals
+// (API key permissions, provider config, routing editors) stop cramming their forms into a
+// 28rem column. Below `sm` they keep the kit's `calc(100vw - 3rem)` width with its 30rem cap
+// lifted (`max-w-none`), i.e. full width minus the mobile gutter. Only `sm` keeps a fixed
+// narrow width — it is the confirm/alert dialog size.
+const WIDE = "max-w-none sm:w-[70vw] sm:max-w-[70vw]";
 const SIZES = {
   sm: "max-w-sm",
-  md: "max-w-md",
-  lg: "max-w-lg",
-  xl: "max-w-xl",
-  full: "max-w-4xl",
+  md: WIDE,
+  lg: WIDE,
+  xl: WIDE,
+  full: WIDE,
 } as const;
 
 // The element focused right now, unless it is <body> (nothing to return to).
diff --git a/tests/unit/ui/modal-width-70vw.test.tsx b/tests/unit/ui/modal-width-70vw.test.tsx
new file mode 100644
index 000000000000..fd556a191bbb
--- /dev/null
+++ b/tests/unit/ui/modal-width-70vw.test.tsx
@@ -0,0 +1,67 @@
+// @vitest-environment jsdom
+import React, { act } from "react";
+import { createRoot } from "react-dom/client";
+import { afterEach, describe, expect, it, vi } from "vitest";
+
+vi.mock("next-intl", () => ({
+  useTranslations: () => (key: string) => key,
+}));
+
+const { default: Modal } = await import("../../../src/shared/components/Modal");
+
+const cleanups: Array<() => void> = [];
+
+function renderModal(props: Partial<React.ComponentProps<typeof Modal>> = {}) {
+  const container = document.createElement("div");
+  document.body.appendChild(container);
+  const root = createRoot(container);
+  (
+    globalThis as typeof globalThis & { IS_REACT_ACT_ENVIRONMENT?: boolean }
+  ).IS_REACT_ACT_ENVIRONMENT = true;
+  act(() =>
+    root.render(
+      <Modal isOpen onClose={() => {}} title="Width" {...props}>
+        body
+      </Modal>
+    )
+  );
+  cleanups.push(() => {
+    act(() => root.unmount());
+    container.remove();
+  });
+  // The kit Dialog (Radix) portals its content to <body>, outside `container`.
+  const dialogs = document.body.querySelectorAll<HTMLElement>('[role="dialog"]');
+  return dialogs[dialogs.length - 1];
+}
+
+afterEach(() => {
+  while (cleanups.length) cleanups.pop()!();
+});
+
+describe("Modal width", () => {
+  it("defaults (md) to ~70% of the viewport from the sm breakpoint, full width below", () => {
+    const dialog = renderModal();
+    // Below `sm` the kit Dialog's own `calc(100vw - 3rem)` width applies (mobile gutter);
+    // `max-w-none` lifts its 30rem cap so the dialog spans the full width minus the gutter.
+    expect(dialog.className).toContain("max-w-none");
+    expect(dialog.className).toContain("sm:w-[70vw]");
+    expect(dialog.className).toContain("sm:max-w-[70vw]");
+    expect(dialog.className).not.toContain("max-w-md");
+  });
+
+  it("uses 70vw for every non-sm size", () => {
+    for (const size of ["lg", "xl", "full"] as const) {
+      const dialog = renderModal({ size });
+      expect(dialog.className, size).toContain("sm:w-[70vw]");
+      expect(dialog.className, size).toContain("sm:max-w-[70vw]");
+      expect(dialog.className, size).not.toMatch(/(^|\s)max-w-(md|lg|xl|4xl)(\s|$)/);
+      cleanups.pop()!();
+    }
+  });
+
+  it("keeps the sm (confirm/alert) dialog narrow", () => {
+    const dialog = renderModal({ size: "sm" });
+    expect(dialog.className).toContain("max-w-sm");
+    expect(dialog.className).not.toContain("70vw");
+  });
+});