Companion

The latest information and downloads the book points you to.

Last updated: 2026-06

Latest info

The fast-changing details the book’s [⚡ Check latest] tags point to. These move quickly — confirm on each service’s official page before you decide.

Gemini: 3.5 Flash (fast, cheap), 3.1 Pro (reasoning), 3 Flash, 3.1 Flash-Lite. Free tier is Flash-only — Pro has been paid since 2026-04.
Claude: Sonnet 4.6 (standard), Opus 4.8 (deep reasoning), Haiku 4.5 (low cost), Fable 5 (top). 1M context.
GPT: GPT-5.5 (flagship), GPT-5.4 family (Mini/Nano), GPT-5.3 Codex (coding).
Principle: Cheap models (Flash/Mini) for high-volume work, top models for paid-tier quality — model tiering is the core of cost control.

Claude Code: Terminal-based agent. Fits the non-coder “control tower” workflow.
Google Antigravity: Agent-first IDE (a VS Code fork) launched Nov 2025. Parallel agents, browser verification. Free preview for individuals.
Cursor: AI-native editor. Popular.
GitHub Copilot: Moved to usage-based (token) billing in June 2026 — long agent sessions can get expensive; set a spend cap.

Paddle: Merchant of Record. Handles global sales and taxes. The practical MoR choice as of 2026.
Stripe Managed Payments: Stripe’s MoR product. ~35 countries only (not Korea/Japan). For Checkout users.
Lemon Squeezy: Acquired by Stripe; effectively in maintenance mode. Not recommended for new projects.

Vercel: Strong for frontend. Hobby is non-commercial — revenue means you need Pro.
Railway: Backend + DB + worker in one. Usage-based ($5 trial, no permanent free tier).
Render: Free static sites.
Fly.io: Free tier removed (2024) — short trial only now.

※ Volatile info — verify on the official page

Copy-and-use design-doc templates and the cost simulator.

Type numbers into the yellow cells and it computes your monthly cost, cost per user, and break-even user count. (Excel · 3 sheets)

Architecture reference, spec doc, stage gates, and more — 8 templates. Copy and use as-is.