Grok 4.20 Beta 0309 (Reasoning) is a flagship large language model developed by xAI, released on March 9, 2026. As a variant of the Grok 4.20 model family, it is specifically optimized for deep reasoning and complex problem-solving. This version features a 2,000,000 token context window, which allows the system to process massive datasets, comprehensive documentation, and long-form codebases in a single session.
The model utilizes a multi-agent reasoning architecture known as the "Council of Four." This internal framework involves specialized agents that collaborate, debate, and cross-check information before a leader agent synthesizes the final response. This approach, combined with inference-time scaling through thinking tokens, enables the model to perform advanced chain-of-thought reasoning for multi-step math, scientific analysis, and logic-heavy tasks.
A distinguishing characteristic of the 4.20 series is its Rapid Learning Architecture. Unlike traditional static models, Grok 4.20 is designed to update its capabilities and refine its performance on a weekly cadence based on real-world usage and feedback. The 0309 build specifically focuses on improving prompt adherence and achieving lower hallucination rates compared to previous iterations.
In addition to its reasoning capabilities, the model supports multimodal inputs, allowing users to upload images for analysis alongside text queries. It is designed for agentic workflows, featuring native support for function calling, structured outputs, and integrated web search to provide grounded, real-time information.