Grok 4.20 Review: xAI's 4-Agent System Sets a Hallucination Record — At a Price

Grok 4.20 (March 10, 2026) is xAI's first model to deploy four specialized internal agents on every Heavy-mode query. AA-Omniscience record: 78% accuracy (lowest hallucination rate ever measured by Artificial Analysis). AI Intelligence Index: 49 — behind GPT-5.4 and Gemini 3.1 Pro (both 57). GPQA Diamond 77.6%, HLE 24.2%. $2/$6/M, 2M context. Rating: 3.5/5.