Elon Musk's mid-September 2026 X posts outlining xAI's rapid Grok roadmap have shaped trader sentiment, detailing Grok 4.8 as a 2.5-trillion-parameter model on a new in-house C++ training stack that would finish pretraining that week before reinforcement learning. Grok 4.7 shipped September 21 at competitive $2/$6 per million tokens pricing, positioned for coding and long-context knowledge work with improvements in self-verification and multi-hour tasks, though independent benchmarks show it trailing leaders like Anthropic's Fable and OpenAI models in some agentic areas. The sequence signals xAI's accelerated cadence—monthly iterations noted earlier—with 4.9 eyed for elite-class performance and Grok 5 as the potential AGI milestone. Key near-term catalysts include confirmation of 4.8 training completion, RL progress, and any benchmark releases or delays that could shift implied probabilities around release windows.