Hydrogen is free to try. The main path is the Gemini app, which needs a Google account.
One plan nuance: our paid work account listed Hydrogen directly in the app's model picker. Google's announcement says free users get Hydrogen through automatic model selection when it's the right model for the prompt, so a free plan may not list it in the picker.
For developers, the Gemini API pricing page lists Hydrogen on a free tier: input and output free of charge. The paid tier is $1.50 per million input tokens and $7.50 per million output tokens (checked November 12, 2026).
Google AI Studio has it on every tier too. It asks for a one-time developer terms acknowledgment first.