Gemini 2.0 Flash Thinking Mode is an experimental model that's trained to generate the "thinking process" the model goes through as part of its response. As a result, Thinking Mode is capable of stronger reasoning capabilities in its responses than the base Gemini 2.0 Flash model.
Google: Gemini 2.0 Flash Thinking Experimental (free) – Provider Status
Providers for Gemini 2.0 Flash Thinking Experimental (free)
OpenRouter routes requests to the best providers that are able to handle your prompt size and parameters, with fallbacks to maximize uptime.