Companion

The latest information and downloads the book points you to.

Last updated: 2026-09-08

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: 3.8 Flash (latest, GA 2026-09-02), 3.7/3.6/3.5 Flash, 3.1 Pro (preview, reasoning), 3.5/3.1 Flash-Lite. The 2.0 line is retired. Free tier is Flash-only — Pro is paid-only.
Claude: Sonnet 5 (standard), Opus 5 (deep reasoning), Haiku 4.5 (low cost), Fable 5.1 (top, 2026-09-01). 1M context on Fable, Opus and Sonnet; Haiku is 200K.
GPT: GPT-6 Astra (flagship, Sept 2026), GPT-5.6 Sol (high), Terra (balanced), Luna (low cost). Same lineup across paid ChatGPT plans, Codex, and the API.
Principle: Cheap models (Flash/Luna) 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: Since 2.0 (May 2026): a parallel-agent desktop app plus CLI, SDK and IDE extensions; the original VS Code-fork IDE remains. Free for individuals with weekly limits; Google AI Pro/Ultra raise them. Free Gemini CLI users were moved to Antigravity CLI in June 2026.
Cursor: AI-native editor. Popular.
GitHub Copilot: Since June 1, 2026: flat fee plus token-based AI Credits. Pro $10 / Pro+ $39 / Max $100 (new), each with matching included credits. Long agent sessions burn credits fast — set a budget.
OpenAI Codex app: Desktop agent for macOS and Windows (included in paid ChatGPT plans). Since April 2026: computer use, browsing, memory and scheduled runs.

Paddle: Merchant of Record. Handles global sales and taxes. The practical MoR choice as of 2026.
Stripe Managed Payments: Stripe’s MoR product. Generally available since April 2026 in 39 countries (Japan yes, Korea no). Checkout and Payment Links only.
Lemon Squeezy: Acquired by Stripe (2024). Still accepting signups with no sunset date announced, but the team is migrating to Stripe Managed Payments — new projects should go to Stripe MP or Paddle.

Vercel: Strong for frontend. Hobby is non-commercial — revenue means you need Pro.
Railway: Backend + DB + worker in one. $5 one-time trial (30 days), then a permanent Free plan with $1/month credit; Hobby $5, Pro $20. Usage-based.
Render: Free static sites.
Fly.io: No free tier — the trial is 2 machine-hours or 7 days, whichever comes first, then a payment method is required.

※ 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.