Grok

Polymarket

Elon Musk

<a href="https://yellow.com/news/grok-openai-anthropic-agentic-ai" rel="noopener noreferrer nofollow">Grok 4.5</a> and <a href="https://yellow.com/news/gpt-56-beats-human-interns-openai" rel="noopener noreferrer nofollow">GPT-5.6</a> launched one day apart, splitting reviewers between OpenAI's 91.9% agentic coding score and <a href="https://yellow.com/news/spacexai-arrives-musk-buries-xai" rel="noopener noreferrer nofollow">SpaceXAI</a>'s $2-per-million-token challenge to frontier pricing.
<h2 id="key-points">Key Points:</h2>
<blockquote>
 <ul>
 <li>GPT-5.6 Sol leads most head-to-head benchmarks, while Grok 4.5 undercuts it on price, speed and token use.</li>
 <li>Independent testers rank Grok 4.5 fourth on intelligence and flag a hallucination rate that doubled to 54%.</li>
 <li>Reviewers favor GPT-5.6 for writing and long coding runs, and Grok 4.5 for high-volume budget work.</li>
 </ul>
</blockquote>
<h2 id="grok-4-5-vs-gpt-5-6-benchmarks">Grok 4.5 Vs GPT-5.6 Benchmarks</h2>
SpaceXAI shipped Grok 4.5 on Jul. 8. OpenAI answered a day later with GPT-5.6, a family that pairs flagship Sol with the cheaper Terra and Luna tiers. Benchmarking firm Artificial Analysis<a href="https://artificialanalysis.ai/articles/grok-4-5-brings-spacexai-to-the-the-intelligence-frontier" rel="noopener noreferrer nofollow">placed</a> the new Grok fourth on its Intelligence Index at 54 points, behind Claude Fable 5, GPT-5.5 and Opus 4.8.
The direct matchup favors OpenAI. One provisional scorecard <a href="https://benchlm.ai/compare/gpt-5-6-sol-vs-grok-4-5" rel="noopener noreferrer nofollow">puts</a> GPT-5.6 Sol at 86 points against Grok 4.5's 82, driven by a 91.9% to 83.3% gap on terminal-based agentic tasks, while coding averages sit in a near tie at 64.7 versus 64.6.
OpenAI <a href="https://openai.com/index/gpt-5-6/" rel="noopener noreferrer nofollow">claims</a> Sol at maximum reasoning sets a record 80 on the independent Coding Agent Index, where Grok 4.5 scores 76 inside its Grok Build harness. The economics run the other way. Grok charges $2 per million input tokens against Sol's $5, and a finished coding task costs $2.49 versus $11.80 for Fable 5.
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<h2 id="coding-writing-and-everyday-tasks">Coding, Writing And Everyday Tasks</h2>
Hands-on reports track the same split: one long-horizon harness <a href="https://www.coderabbit.ai/blog/gpt-5-6-sol-and-terra-benchmark" rel="noopener noreferrer nofollow">found</a> Sol finished 63.7% of more than 100 real repository tasks without trial errors, staying oriented through messy multi-step checklists. A separate independent coding test <a href="https://akitaonrails.com/en/2026/07/09/llm-benchmark-grok-4-5-gpt-5-6-sol/" rel="noopener noreferrer nofollow">scored</a> Sol at 92 out of 100 and Grok 4.5 at 87, level with the best open-weights models.
Writers lean the same way, with early testers <a href="https://every.to/vibe-check/gpt-5-6-sol" rel="noopener noreferrer nofollow">describing</a> Sol as a daily driver that now covers roughly 80% of routine knowledge work and follows style guides more faithfully than rivals.
Grok 4.5 answers with speed and obedience. Reviewers who ran it on live jobs <a href="https://theplanettools.ai/tools/grok-4-5" rel="noopener noreferrer nofollow">reported</a> clean first-attempt builds, reliable structured output and sub-five-second responses at about 80 tokens per second. Accuracy is the catch, because its measured hallucination rate jumped from 25% to 54% even as factual accuracy improved to 52%.
<h2 id="expert-verdicts-and-trust-questions">Expert Verdicts And Trust Questions</h2>
Elon Musk<a href="https://www.metirai.com/blog/groks-comeback-grok-4-5-xai-review-2026" rel="noopener noreferrer nofollow">billed</a> Grok 4.5 as "an Opus-class model, but faster, more token-efficient and lower cost." Some analysts <a href="https://the-decoder.com/grok-4-5-is-so-cheap-compared-to-fable-5-and-gpt-5-5-that-benchmark-gaps-may-not-matter-much/" rel="noopener noreferrer nofollow">argued</a> the price gap outweighs the score gap, since Grok burns 1.9 million tokens per task against Fable 5's 7.2 million.
Skeptics see reasons for caution. Reviewers <a href="https://letsdatascience.com/blog/grok-4-5-opus-class-claim-ranks-fourth" rel="noopener noreferrer nofollow">noted</a> that launch scores were vendor-reported, that no model card shipped, and that Cursor withdrew one internal benchmark after Grok accidentally trained on its codebase. GPT-5.6 carries its own asterisk, since OpenAI's system card <a href="https://www.eesel.ai/blog/gpt-5-6-review" rel="noopener noreferrer nofollow">admits</a> the model oversteps instructions more often than its predecessor.
The rivalry capped a turbulent stretch: SpaceX absorbed xAI in February, bought Cursor for $60 billion in June and rebranded the lab SpaceXAI two days before Grok 4.5 arrived. OpenAI spent late June with Sol locked in a government review, while <a href="https://yellow.com/news/fable-5-returns-without-hacker-power" rel="noopener noreferrer nofollow">Anthropic's Fable 5</a>, still the published benchmark leader, only returned Jul. 1 from a 19-day suspension.
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