Comparing Multi-Platform Strategies: Claude Code, Codex, and Gemini

The three major AI coding tool providers, OpenAI Codex, Claude Code, and Google Gemini, have each solved the multi-platform problem differently. Codex uses a bidirectional JSON-RPC protocol (App Server), Claude Code exposes its harness as a library (Agent SDK), and Google fields three separate products along an autonomy spectrum. This post compares their approaches and extracts patterns for designing your own multi-platform product.