Grok 4 Fast Reasoning is xAI's cost-efficient large-context model that targets near-frontier quality while dramatically reducing per-token costs. It delivers strong reasoning and instruction following on complex math, coding, and analytical tasks, landing between frontier models and earlier Grok generations in overall quality. Compared with Grok 4.1 Thinking it sacrifices a bit of peak text quality and creativity in exchange for much higher throughput, making it a great default for production assistants and agentic tools that need both depth and speed.