Author and run E2E tests on a cloud browser grid - BrowserStack Automate, Sauce Labs, or LambdaTest. All three follow one pattern: username + access-key env vars, a W3C WebDriver hub URL, a vendor options dict inside the capabilities (bstack:options / sauce:options / LT:Options), a local tunnel binary for internal apps, session pass/fail reporting, and a CI matrix throttled to the plan's parallel-session limit. Worked example uses BrowserStack; per-vendor deltas live in references/. Use for cross-browser regression on real devices + browsers beyond the engines bundled on the local machine - distinct from a local matrix runner and from self-hosted Selenium Grid.