Gemini 3.5 Flash Function Calling: Build a Tool-Using Agent

On May 19, 2026 at Google I/O, Google shipped Gemini 3.5 Flash straight to general availability — no preview tag. The headline number was speed (~4x the output tokens per second of comparable frontier models), but the more interesting line in the docs was the positioning: this is a model built for the agentic era, tuned for sub-agent deployment, rapid tool-use loops, and long-horizon multi-step work.

A fast model is only useful as an agent if it can do things — call your code, read the result, and decide what to do next. That capability is function calling. In this guide you'll wire Gemini 3.5 Flash to two real Python functions and build a working agent loop that can chain multiple tool calls in a single turn, feed results back, and produce a grounded final answer.