Each chapter covers the same five things: the configuration surface, the caching model, the delegation and tool model, the controls that matter, and what is distinctive. Chapters are ordered alphabetically by product, which is the only ordering that carries no implied ranking. Prices are as published on 8 September 2026 and move faster than anything else here.
Claude and Claude Code
Claude and Claude Code on the same five questions: configuration surface, caching model, pricing, delegation and tools, and controls worth setting.
OpenAI and Codex
OpenAI and Codex: configuration surface, caching model, prompt cache keys, pricing, and the distinctive features.
GitHub Copilot
GitHub Copilot: configuration surface, the multi-surface problem, the consumption model, and controls worth setting.
Cursor
Cursor: the rules system, why always-apply stays small, rules and AGENTS.md together, and what is distinctive.
Gemini
Gemini: two caching mechanisms, the storage meter that changes the arithmetic, hit reliability, and pricing notes.
Writing Once and Running Everywhere
A platform crosswalk, the portable core, prompting to the intersection, and what is not worth trying to unify.