Model comparisons - tested October 2026 by Vitus Pruser. How we test.
Verdict
GPT-6 Astra took 9 of 10 prompts: fuller emails, all-facts rewrites, code whose own tests pass, and data answers with richer tables. Grok 4.3 won only the jug puzzle on tersest correct answer, but the real story is the price: the whole ten-prompt round cost Grok $0.02 against GPT-6 Astra's $0.21, at 3 seconds faster per answer on average. For anything that must be right pick GPT-6 Astra; for quick drafts and everyday questions Grok is the bargain on Krater.
Verdict by task
| Task | Winner | Why |
|---|
| Writing | GPT-6 Astra | Grok produced functional but flatter copy and dropped the exponential-versus-linear contrast in the rewrite; GPT-6 Astra kept every fact and read better. |
| Coding | GPT-6 Astra | Grok's slugify failed one of its own tests (its accent map misses ï) and its rounding fix silently changes policy; GPT-6 Astra passed everything, at the cost of one npm dependency. |
| Research | GPT-6 Astra | Both were correct on the EU VAT headline figure, but Grok omitted the €85,000 national cap nuance and cited Worldometer instead of the UN on populations. |
| Data analysis | GPT-6 Astra | Both computed every figure correctly; GPT-6 Astra added change-in-euros columns and multi-metric best and worst breakdowns. |
| Reasoning | Split | Both solved both puzzles. Grok won the water jug for the tersest optimal answer; GPT-6 Astra won the bill split on presentation. |
Results, prompt by prompt
writing - winner: GPT-6 Astra
Prompt: Write a 120 word product update email to existing customers of a small accounting software company announcing that bank feeds now sync every hour instead of once a day. Plain, friendly, no exclamation marks, end with one clear call to action.
- Grok 4.3 - pass, no hallucinations, 16.1s. 103 words, functional but flat: a "Thank you for being a customer" opener and the weakest flow.
- GPT-6 Astra - pass, no hallucinations, 16.1s. 124 words, plain and friendly, ends with a clear log in call to action. No subject line.
writing - winner: GPT-6 Astra
Prompt: Rewrite this paragraph so a 12 year old understands it, keep every fact, max 80 words: 'Compound interest is interest calculated on the initial principal and also on the accumulated interest of previous periods. Because the base grows each period, the growth is exponential rather than linear, which is why long time horizons matter far more than the interest rate alone.'
- Grok 4.3 - pass, no hallucinations, 11.3s. 46 words and loses the exponential-versus-linear contrast; "grows fast like doubling" is looser.
- GPT-6 Astra - pass, no hallucinations, 12.5s. 66 words, keeps every fact including exponential versus linear growth. Cleanest rewrite.
coding - winner: GPT-6 Astra
Prompt: Write a Python function slugify(title: str) -> str that lowercases, replaces any run of non alphanumeric characters with a single hyphen, strips leading and trailing hyphens, and transliterates common accented Latin letters (e, a, o, u with accents, and the German sharp s) to ASCII. Include 5 pytest test cases. No external dependencies.
- Grok 4.3 - partial, no hallucinations, 15s. 4 of its own 5 tests pass: its transliteration map misses ï, so its own naïve test case fails.
- GPT-6 Astra - pass, no hallucinations, 22.6s. Leanest correct solution: casefold() handles ß naturally. All 5 tests pass and it survives extra edge cases (Ü, Ñ).
coding - winner: GPT-6 Astra
Prompt: This JavaScript has a bug: users report the total is sometimes off by one cent. Find the bug, explain it in two sentences, and give the corrected function.
function total(items) {
let sum = 0;
for (const it of items) {
sum += it.price * it.qty * (1 + it.taxRate);
}
return Math.round(sum * 100) / 100;
}
- Grok 4.3 - partial, no hallucinations, 14.6s. Per-line integer cents fixes accumulation, but silently changes the rounding policy and still misses the 4.01 boundary case.
- GPT-6 Astra - pass, no hallucinations, 17s. Correct diagnosis and a Decimal.js fix that is exact on every boundary case, but it adds an npm dependency.
research - winner: GPT-6 Astra
Prompt: What is the current EU VAT registration threshold for small businesses under the EU wide SME scheme that started in 2025, in euros, and which regulation introduced it? Answer in 3 sentences and say if you are unsure about any figure.
- Grok 4.3 - pass, no hallucinations, 9.8s. Correct on €100,000 and Directive 2020/285, but omits the €85,000 national cap the question asked about.
- GPT-6 Astra - pass, no hallucinations, 13.4s. Correct figures (€100,000 union threshold, €85,000 national cap), correct instrument (Directive 2020/285), and honestly flags it cannot verify later amendments.
research - winner: GPT-6 Astra
Prompt: List the 5 largest countries by population in 2024 with their approximate population, and name the source you would cite for these figures. Table format.
- Grok 4.3 - pass, no hallucinations, 9.8s. Right ranking, but cites Worldometer instead of the UN primary source; figures ~4 to 6m low.
- GPT-6 Astra - pass, no hallucinations, 11s. Most precise figures (India 1.451b, China 1.419b), matching UN World Population Prospects 2024 mid-year estimates, with the source named.
data - winner: GPT-6 Astra
Prompt: Here are monthly revenue figures in EUR for a shop: Jan 41200, Feb 38900, Mar 45100, Apr 47800, May 46200, Jun 52300, Jul 55900, Aug 51400, Sep 58700. Compute the month over month growth for each month, the average growth rate, and the best and worst month. Show the numbers in a table and state the totals.
- Grok 4.3 - pass, no hallucinations, 13.4s. Every number correct, bare-minimum presentation.
- GPT-6 Astra - pass, no hallucinations, 20.6s. Every month over month figure correct (avg 4.90%), plus euro changes, totals and a multi-metric best and worst table.
data - winner: GPT-6 Astra
Prompt: A SaaS company has 1,240 customers paying an average of 49 EUR per month and loses 3.1 percent of customers each month. New signups are 85 per month. Estimate the customer count and MRR after 12 months assuming these rates hold. Show your working and round to whole numbers.
- Grok 4.3 - pass, no hallucinations, 18.2s. Correct 1,713 and 83,937, self-verifies by iteration. Concise.
- GPT-6 Astra - pass, no hallucinations, 23s. Closed-form solution, 1,713 customers, MRR 83,920 computed on the unrounded count, which is the more rigorous route.
reasoning - winner: Grok 4.3
Prompt: I have a 3 litre jug and a 5 litre jug and unlimited water. Give the shortest sequence of steps to measure exactly 4 litres. Then say how many steps it took.
- Grok 4.3 - pass, no hallucinations, 8.7s. Optimal 6 steps and the tersest answer of the five: exactly what the prompt asked.
- GPT-6 Astra - pass, no hallucinations, 11.1s. Optimal 6 steps with per-step jug states shown.
reasoning - winner: GPT-6 Astra
Prompt: Three colleagues need to split a 187 EUR dinner. Anna had no drinks and her food was 41 EUR. Ben and Clara shared two bottles of wine totalling 58 EUR and their food was 44 EUR each. Who owes what, so that everyone pays exactly for what they consumed? Show the check that the parts add up to 187.
- Grok 4.3 - pass, no hallucinations, 8.6s. 41, 73, 73, correct, with a short method note.
- GPT-6 Astra - pass, no hallucinations, 8.6s. 41, 73, 73, check to 187. Correct and cleanest.
Try both on Krater
Tested inside the Krater Model Arena. Run the same prompts yourself - Grok 4.3 and GPT-6 Astra are both in one subscription.
Open Krater chat · Grok 4.3 · GPT-6 Astra
Frequently asked questions
Is Grok or ChatGPT better?
In our October 2026 round, GPT-6 Astra ranked first on 9 of 10 prompts in a blind review; Grok 4.3 won only the water jug puzzle on brevity. But Grok answered every prompt at roughly a tenth of the cost and faster on average, so for everyday questions the gap in quality may not justify the gap in price for you.
Is Grok or ChatGPT better for coding?
GPT-6 Astra, clearly. Its slugify passed all five tests including extra edge cases, while Grok 4.3 failed its own naïve test case and produced a rounding fix that quietly changes the rounding policy. Grok is fine for quick scripts, not for code you ship.
Which is cheaper, Grok or ChatGPT?
Grok by a wide margin. Across the ten prompts Grok 4.3 cost $0.02 in total against $0.21 for GPT-6 Astra, and answered about 3 seconds faster on average.
Can I use Grok and ChatGPT in the same place?
Yes. Krater gives you Grok 4.3, GPT-6 Astra and 500+ other models in one workspace, and the Model Arena sends one prompt to several models side by side, which is how this comparison was run.
How was this comparison tested?
All five models (GPT-6 Astra, Claude Fable 5.1, Gemini 3.1 Pro Preview, Grok 4.3 and Perplexity Sonar Pro) received the same ten prompts side by side in the Krater Model Arena on 7 October 2026, with default settings and no system prompt; this page compares the two you are looking at. We recorded time to a complete answer and the real model cost per answer, ran the generated code through its own test suites, fact checked every claim, scored completion as pass, partial or fail, and then ranked the answers blind. The full procedure is on our methodology page.
Will this comparison be updated?
Yes. Flagship comparisons are rerun monthly and whenever a provider ships a new version. The tested month and model versions are shown at the top of the page.
