Vals published a benchmark pass for Grok 4.20 Beta showing gains on coding, math, multimodal, and Terminal Bench 2, alongside weaker legal-task results. Check task-level results before adopting it, especially if legal workflows matter more than headline benchmark gains.
Vals' benchmark pass says Grok 4.20 Beta improved over Grok 4.1 Fast on a broad set of engineering-relevant tests, including AIME, GPQA, IOI, LiveCodeBench, SWE-Bench, and Terminal Bench 2 coding gains. The same thread says Vibe Code Bench rose from "1% to ~4%," a small absolute number but still a measurable gain on a test for building web apps from scratch coding gains.
The clearest single delta was ProofBench. Vals says the model "jumps up to 14%" from 4% on a benchmark for formally verified graduate-level math proofs ProofBench jump. On the multimodal side, Vals reports 83.47% and a #9 MMMU ranking, up from #31 for Grok 4.1 Fast, plus improvement on SAGE for grading handwritten solutions multimodal gains.
Vals says the model is "generally quite fast," with per-test latency on the Vals Index at roughly 20% to 50% of higher-performing models latency note. The benchmark card in Vals' post lists 85.58s latency, $0.28 cost per test, and a 2M context window and max output size for this snapshot benchmark card.
The same evaluation thread also flags two reasons not to overread the headline gains. First, legal-task performance lagged: Vals reports rankings of #30 on CaseLaw and #62 on LegalBench, calling out "less improvement or even regressions" on legal benchmarks legal regressions. Second, these numbers come from a beta snapshot run at temperature 0.7 and top_p 0.95 through the xAI API endpoint grok-4.20-beta-0309-reasoning, and Vals says performance may change in later releases eval settings beta caveat.
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We’ve finished evaluating the Grok 4.20 Beta (Reasoning) snapshot on our full suite of benchmarks. We find it to be an overall improvement over Grok 4.1 Fast (Reasoning).
Evaluations were run with a temperature of 0.7 and a `top_p` of 0.95 via the @xai API using the grok-4.20-beta-0309-reasoning endpoint. Full results are available on Vals AI.
The model is generally quite fast. On the Vals Index, it is approximately 20% to 50% of the latency (on a per-test basis) of higher performing models.
