LiveKit tests Gemini 4 Hydrogen vs 3.8 Flash in a voice agent with deliberately broken tools

LiveKit ran Gemini 4 Hydrogen and Gemini 3.8 Flash through the same Google plugin in a voice travel-concierge agent with deliberately failing tools, and Hydrogen made 0 false booking reports across 54 transcripts versus 2 for 3.8 Flash. With Hydrogen at high and 3.8 Flash at default, Hydrogen's first sentence arrived 1.2 s sooner (4.0 s vs 5.2 s), and at low on both it was 1.7 s sooner (2.8 s vs 4.6 s). The author recommends medium or high thinking for voice agents, noting xhigh's median 7.8 s to first sentence and a 52 s worst case.