Mathew Pregasen announced the beta of Letterpress-1 from The Letter Company, a New York team in Y Combinator's Fall 2026 batch. The product is for teams that keep a marketing site in git. It reads the site and outside signals, including agent traffic, search rankings, human visits, and competitor activity, then builds the change in a sandbox and opens a pull request with a live preview. The team decides whether that change stays a preview, becomes a pull request, or merges after checks pass. Letterpress-1 runs in Build, Plan, and Fix. Build creates pages and copy that stay inside the existing brand. Plan turns a growth goal into work that ships in the repository. Fix finds issues on the marketing site and opens pull requests to correct them. It can also propose the next growth task, such as visitor de-anonymization, experimental landing pages, warmed email, blog automation, and agent telemetry. Teams can ask from the web app, Slack, or the letterpress command in a repo, or press Command-L on the live site, edit the text in place, and send that edit into a pull request. The same tools are exposed over MCP, so an agent the team already uses, including Claude Code or Codex, can call them. Letter says the system mixes frontier models with smaller fine-tuned models, runs on its hosted platform with no local GPU, and can be installed against a repository in under five minutes. The beta is aimed at a change the company describes in the launch: models are increasingly the ones deciding which products to recommend, and they want evidence and context before they do. After install, Letterpress-1 is meant to measure and flag issues around agent conviction, SEO, GEO, and inbound conversion, then ship the fixes as pull requests. It also includes four primitives for that kind of work. Proofs are evidence chains meant to show agents real usage, repeat customers, and outcomes. Simulations are mirror applications an agent can try before a purchase. Phantoms are autonomous sites for testing growth strategies in a sandbox. Benches are self-hosted benchmarks with independent, open-source governance. These sit on Slack, Git, and MCP. Paid plans start at $100 a month for 10,000 tokens, and new accounts get 5,000 free tokens, or 6,000 with a work email.