Simulithic sends AI agents through a web app the way real users would, across browsers, devices, and account types, then reports what broke without anyone writing a test script. It is for engineering teams that can generate changes quickly with coding agents, but still check those changes with hand-written Playwright tests or manual clicks before a deploy. The YC Fall 2026 launch targets the gap that opens when code is written in minutes and verification still takes hours. A command called simulithic map points the agents at an app so they explore it and map user flows on their own. Each flow runs in its own virtual machine against the browsers, devices, screen sizes, and network speeds customers actually use, including Safari, Chrome, and Firefox on macOS, Windows, iOS, and Android. The same checks can run from the terminal or from Claude Code and Codex before a pull request, as the end-to-end step in CI with a comment on the pull request, and against production as often as every 30 minutes, with a Slack alert if a live flow fails. When the interface changes, the agents adapt, so there is no script library to keep rewriting. Ryan Ning (CEO) and Satyam Singh (CTO) founded the San Francisco company. Ning previously worked at Uber and Shopify and researched AI agents at the University of Toronto. Singh previously worked at Ramp and at Bree (YC S21), and is a NASA Space Apps Challenge winner. They started Simulithic after running into the same slow verification step while shipping at those companies.