[AI in Practice] Upgrading from Gemini 3.5/3.6 to Gemini 4 Argon: Migration Notes and Pitfalls for LINE Bot Developers

Google has officially released Gemini 4 Argon, introducing significant changes to parameter specifications, token management, and caching mechanisms. For developers migrating existing LINE Bots from Gemini 3.5 or 3.6, a simple model swap is insufficient. Key pitfalls include the new unified 1M token window, where thinking tokens consume the output budget, and the deprecation of explicit caching in favor of automatic implicit caching. Developers must also navigate the shift from legacy generateContent to the new Interactions API, which supports background processing essential for handling long-running tasks without timing out LINE webhooks. Furthermore, standard sampling parameters like temperature are now ignored, and strict rules regarding model-role turns have been enforced. The author recommends a hybrid architecture: using lighter models for instant replies and routing complex, heavy-reasoning tasks to Gemini 4 Argon via the asynchronous Interactions API to ensure optimal performance and cost-efficiency.