Gemini Interactions API: Build Stateful AI Agents

At Google I/O on May 19, 2026, Gemini 3.5 Flash went generally available and Google quietly changed how it wants you to build. The docs now open with a line that matters: for new projects, use the Interactions API (Beta). It is the new standard, optimized for agentic workflows, server-side state, and the capabilities Google says will ship exclusively on it going forward. The old generateContent API is still fully supported, but the center of gravity has moved.

The single biggest practical change is state. With generateContent you resend the entire conversation history on every turn. With Interactions, the server keeps the history for you and you reference it by ID. That one shift removes a whole class of bugs around dropped thought signatures, mismatched tool IDs, and ballooning request payloads.