Grok 4.5 vs Claude Opus 4.8 vs GPT-5.5: Which Should You Use?

Quick answer: Grok 4.5 (launched July 8, 2026) lands at #4 on Artificial Analysis' Intelligence Index — just behind Claude Opus 4.8 and GPT-5.5 — while costing a fraction of both: $2/$6 per million tokens vs $5/$25 for Opus and $5/$30 for GPT-5.5. It's not the benchmark king; it's the price disruptor. And as of today, it's live on TulexAI at 2 PT per message.

xAI (now SpaceXAI, post-IPO and fresh off the Cursor acquisition) shipped Grok 4.5 with a bold framing from Musk: "an Opus-class model, but faster, more token-efficient and lower cost." Worth noting his own caveat — the internal comparison was against Opus 4.7, not the current 4.8. So how does it actually stack up? Here are the numbers, with sources and the caveats vendors leave out.

The price gap is the headline

Model	Input / 1M tokens	Output / 1M tokens	Context window	On TulexAI
Grok 4.5	$2.00	$6.00	500k	2 PT / message
Claude Opus 4.8	$5.00	$25.00	1M	3 PT / message
GPT-5.5	$5.00	$30.00	—	5 PT / message
Fable 5	$10.00	$50.00	—	Suspended by Anthropic since June 2026

Per API token, Grok 4.5 is roughly 4–5× cheaper than Opus 4.8 and GPT-5.5 on output — and it's stingy with those tokens too. On SWE Bench Pro tasks it averaged ~15,954 output tokens per task vs Opus 4.8's 67,020: about 4.2× fewer tokens for the same work (xAI's measurement; Artificial Analysis independently found ~60% fewer output tokens per task than Opus). The-Decoder's launch-day take captured the mood: it's "so cheap compared to the frontier that benchmark gaps may not matter much."

What do the benchmarks actually say?

On Artificial Analysis' independent Intelligence Index — the closest thing to a neutral scoreboard — Grok 4.5 scores 54, ranking #4 of 168 models: behind Fable 5 (60), Claude Opus 4.8 (56), and GPT-5.5 (55), and a full 16 points above its predecessor Grok 4.3 (38). That's a frontier model, one notch below the very top.

Coding, on the neutral harness (not the vendor's own):

Benchmark	Grok 4.5	Claude Opus 4.8	GPT-5.5	Fable 5
DeepSWE 1.1 (neutral harness)	53%	59%	67%	70%
Terminal Bench 2.1	83.3%	78.9%	83.4%	84.3%
SWE Bench Pro (resolve)	64.7%	69.2%	58.6%	80.4%
Cost per coding-agent task (AA)	$2.59	$5.07 (GPT-5.5) / $11.80 (Claude Code)		$11.80

Read the table honestly: Grok 4.5 does not top a single quality benchmark against the frontier. It trades blows — beating Opus on Terminal Bench, beating GPT-5.5 on SWE Bench Pro — at a quarter to a half of the cost per task. On Artificial Analysis' agentic tool-use test (τ³-Banking) it posted the single best score on the board at 33%. It also measured ~89.5 tokens/sec serving speed, more than twice GPT-5.5's typical throughput.

Caveat that matters: the first table rows above come from launch-day coverage of xAI's announcement plus Artificial Analysis; BenchLM notes xAI published only ~6 benchmarks and third-party coverage is still filling in. Treat vendor-reported numbers as claims, not facts.

The trade-off nobody headlines

We sell honest billing, so here's the honest catch: on Artificial Analysis' Omniscience factuality test, Grok 4.5's accuracy jumped (35% → 52% vs Grok 4.3) but its hallucination rate more than doubled — 25% → 54%. When it doesn't know, it now guesses confidently more often. xAI's launch post didn't mention it. For research and fact-heavy work, keep a search-grounded model (or TulexAI's web-search toggle) in the loop and treat unverified claims accordingly. Two more launch-day footnotes: the context window is 500k — big, but smaller than Grok 4.3's 1M — and xAI's own consumer apps hadn't rolled out in the EU at launch. TulexAI integrates via the xAI API, so it's available on every TulexAI plan today.

Who should use which?

• Pick Grok 4.5 when: you want frontier-adjacent reasoning at mid-tier prices — agentic tasks, coding iteration, long working sessions where output-token burn adds up. It's the new best value-per-answer in the premium tier.
• Pick Claude Opus 4.8 when: you need the most reliable long-form writing, careful instruction-following, and fewer confident errors — and the 1M context for huge documents.
• Pick GPT-5.5 when: you want the strongest all-round coding harness (DeepSWE 67%) and the deepest ecosystem of tooling.
• What about Fable 5? It tops nearly every board in the tables above — but Anthropic suspended public access to it in June 2026, so for most people the practical Anthropic flagship is Opus 4.8. The benchmark rows stay because that's who xAI chose to compare against.

The part where one subscription beats four

Here's the thing about "which model should you use": the honest answer changes month to month — Grok 4.5 didn't exist last week. A SuperGrok subscription runs ~$30/mo for one vendor. On TulexAI, Grok 4.5 costs 2 PT per message (Premium tier) alongside Claude Opus 4.8, GPT-5.5, Gemini 3.1, and 50+ other models — from $11/mo, with a live token meter showing exactly what each message costs before you send it. Run the same prompt through all three and pick the winner yourself; that's the whole point.

Try Grok 4.5 free on TulexAI — no card, and your first prompts are on us. Already paying for Grok, Claude, or ChatGPT separately? Bring your chat history with you.

Frequently Asked Questions

Is Grok 4.5 better than Claude Opus 4.8?

On neutral scoreboards, no — Opus 4.8 ranks slightly higher on Artificial Analysis' Intelligence Index (56 vs 54) and wins on SWE Bench Pro. But Grok 4.5 beats Opus on Terminal Bench, uses roughly 4× fewer output tokens per task, and costs $2/$6 per million tokens against Opus' $5/$25. Better per dollar: usually Grok. Better per answer on hard writing and reliability: Opus.

How much does Grok 4.5 cost?

Via the xAI API: $2.00 per million input tokens, $6.00 per million output tokens, and $0.50 for cached input (verified against docs.x.ai, July 2026). On TulexAI it's 2 Platform Tokens per message on any plan, from $11/mo — no separate xAI subscription needed.

What is Grok 4.5's context window?

500,000 tokens (per xAI's docs). That's large, but notably smaller than both Claude Opus 4.8's 1M and Grok 4.3's 1M — so for very large documents the older Grok or Opus can still be the right pick.

Does Grok 4.5 hallucinate more than other models?

The independent data says yes: Artificial Analysis measured a 54% hallucination rate on its Omniscience test, up from 25% for Grok 4.3, even though overall accuracy improved. For fact-critical work, pair it with web search or double-check with a second model — both one click on TulexAI.

Can I use Grok 4.5 without a SuperGrok subscription?

Yes. TulexAI includes Grok 4.5 through the xAI API on every plan at 2 PT per message, alongside 50+ other models. That replaces a ~$30/mo SuperGrok subscription — and everything else you'd subscribe to separately — from $11/mo.