Gemini Flash vs Pro: Comparing Google's Latest LLMs

Google's Gemini 2.5 Flash and 2.5 Pro differ mainly in speed versus reasoning depth, both offering 1M-token context windows and native availability in Vapi for voice agents. Flash returns its first token in 0.21–0.37 seconds at 163 tokens per second and costs $0.15/$0.60 per million input/output tokens, while Pro costs $1.25/$10 and adds a Deep Think mode, with a 2M-token window planned.