Grok 4.20 (also written Grok 4.2) is xAI’s Grok release of early 2026, following Grok in the corpus’s lineage. It first appears as an internal beta that a UC Irvine mathematician gave an open problem in harmonic analysis, and which found a novel Bellman function in five minutes (X). In February Musk claimed it features continuous post-training that will let it improve every week, a promise the corpus records its successor Grok 4.3 making good on by improving every few days.
AISystem
Grok 4.20
xAI's early-2026 Grok release, first seen as an internal beta that solved an open harmonic-analysis problem and later claimed by Musk to keep learning after shipping.
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- Welcome to January 15, 2026 (theinnermostloop.substack.com)
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