Grok 4.3 vs GPT-5.5
Cheap specialist vs expensive flagship.
xAI shipped Grok 4.3 on April 30, 2026. OpenAI shipped GPT-5.5 a week earlier on April 23. They aren't aiming at the same market. GPT-5.5 is smarter overall. Grok 4.3 is roughly 10x cheaper and beats it on legal reasoning, corporate finance, and certain agentic workloads. The right answer depends entirely on what you're doing.
OpenAI
GPT-5.5 wins on…
- →Intelligence Index (60 vs 53)
- →Terminal-Bench 2.0 (82.7%)
- →General coding (Grok ranks 13th)
- →Agent reliability (no idle / narcolepsy)
xAI
Grok 4.3 wins on…
- →Price (~10x cheaper per token)
- →Legal reasoning (#1 on CaseLaw v2)
- →Corporate finance (#1 on CorpFin)
- →Agentic knowledge work (GDPval-AA ELO 1500)
GPT-5.5 is the smarter generalist. Grok 4.3 is the cheap specialist. Most teams need both.
Grok 4.3 is roughly 10x cheaper
xAI deliberately undercut the market. This is the most aggressive frontier-model pricing shipped in 2026.
GPT-5.5
Grok 4.3
What this means in practice
On a typical workload with a 3:1 input-to-output ratio, Grok 4.3 ends up roughly 6–8x cheaper per task than GPT-5.5. For pure output-heavy work (long generations, agentic loops, synthesis), the gap widens to 12x. The independent benchmark suite Artificial Analysis costs current plan details to run on Grok 4.3 vs nearly 10x more on GPT-5.5.
Benchmark by benchmark
Where each model wins and loses. Green cell marks the leader.
| Benchmark | What it measures | GPT-5.5 | Grok 4.3 |
|---|---|---|---|
| Intelligence Index | Composite reasoning + knowledge + math + code | 60 | 53 |
| CaseLaw v2 | Legal reasoning | ~73% | 79.3% (#1) |
| CorpFin | Corporate finance reasoning | ~76% | #1 |
| GDPval-AA (agentic) | Real-world knowledge work | ELO ~1450 | ELO 1500 |
| Tau²-Bench Telecom | Customer-service workflows | 98.0% | leading |
| Terminal-Bench 2.0 | Command-line agent work | 82.7% | ~64% |
| General coding (Vals AI rank) | Cross-language coding tasks | Top 3 | 13th |
| FrontierMath (1–3) | Olympic-level mathematics | 51.7% | ~38% |
| IFBench | Instruction following | strong | leading |
| Native video input | Direct video frame processing | — | ✓ |
| Cost to run Intelligence Index | current plan details | current plan details | |
Sources: artificialanalysis.ai, Vals AI, Andon Labs, official launch announcements (April–May 2026). Methodology varies between labs — treat as directional.
Three things the benchmarks reveal
The interesting stories aren't in the headline numbers. They're in the gaps.
Always-on reasoning beats general intelligence in legal & finance
#1 on CaseLaw v2 + CorpFin
Per Vals AI, May 2026
Grok 4.3's "reasoning is permanently active, not toggleable" architecture turns out to be remarkably well-suited to dense, structured domains where every claim needs to be traced through a chain of logic.
On CaseLaw v2 (legal reasoning), Grok 4.3 hit 79.3% accuracy — a 25-point jump over its predecessor and the top score from any model tested. Same #1 ranking on CorpFin. For law firms, M&A advisory, contract review, and regulated finance work, this is the better tool — and at 1/10th the cost of GPT-5.5, the math is hard to argue with.
Still the smarter generalist
60 vs 53
Artificial Analysis Intelligence Index
For broad reasoning across math, science, code, and general knowledge work, GPT-5.5 remains meaningfully ahead. The 7-point Intelligence Index gap (60 vs 53) shows up consistently across hard math (FrontierMath), Terminal-Bench, and general coding evaluations.
If you need one model to be reliably good at everything you might throw at it, GPT-5.5 is the safer pick. For unattended agents that can't have idle moments, the gap is even bigger — Andon Labs reported Grok 4.3 sometimes "preferring to sleep for multiple days in a row over taking actions."
xAI shattered the reasoning-model price floor
~10x cheaper
Per-token cost vs GPT-5.5
Grok 4.3 brings the price of "1M context + always-on reasoning" to roughly 1/12th of Claude Opus 4.7. That's not a small adjustment. It's an explicit attempt to break the industry consensus that reasoning models have to be expensive.
The downstream signal: OpenAI and Anthropic are likely to either follow with cuts in the back half of 2026 or differentiate further on quality — better coding, longer memory, deeper agent capabilities. For users right now, it means workloads that were too expensive to justify on GPT-5.5 might suddenly be economical on Grok 4.3 even if they need slightly more effort.
When to reach for which
Reach for GPT-5.5
- →Production software engineering and complex coding
- →Unattended agents that can't afford idle time
- →Hard math, scientific reasoning, FrontierMath-style problems
- →Terminal automation, DevOps pipelines
- →General-purpose use where breadth matters more than cost
Reach for Grok 4.3
- →Legal research, contract analysis, regulated work
- →Corporate finance, M&A modeling, financial reasoning
- →High-volume agentic tasks where cost dominates
- →Customer service / structured workflow automation
- →Video input — direct frame processing without transcription
- →Document generation: PDF, XLSX, PPTX directly in chat
Stop picking. Route by task.
Different tasks have different right answers. Cheap specialist for one, expensive flagship for another. MultipleChat AI gives you both — and three more frontier models — with current plan details.
Subscribe to both
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ChatGPT Plus + SuperGrok
SuperGrok Heavy alone
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One ecosystem, 16-Agent mode
MultipleChat AI
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Both — and 3 more models
Why this works for the Grok-vs-GPT split
When you have both, you stop optimizing for one and start routing by task.
Compare Mode
Send the same prompt to GPT-5.5 and Grok 4.3 in parallel. See which is right on YOUR specific task — not which won a benchmark someone else ran.
Sources & Disagreements
When the models disagree on a legal citation or a financial figure, you see exactly where. That's where one is right and the other is hallucinating.
AI Collaboration modes
Have Grok 4.3 draft the legal analysis (cheap, specialized), GPT-5.5 review for general accuracy (smart, broad). Cooperative, Verification, Chain — ten interaction modes.
Always the latest API versions
When xAI ships Grok 4.4 or OpenAI ships GPT-5.6, you get them through the same subscription. No re-subscribing, no migrating.
Plus Claude, Gemini, Perplexity Sonar
Three more frontier models. Claude for nuanced writing and SWE-bench-leading coding. Gemini for the longest documents. Sonar for source-grounded research.
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Frequently Asked Questions
GPT-5.5 is smarter overall — it scores 60 on the Artificial Analysis Intelligence Index versus Grok 4.3's 53, and leads on most general benchmarks. But Grok 4.3 costs about 1/10th as much per token and wins specific niches: legal reasoning (CaseLaw v2 #1 at 79.3%), corporate finance (CorpFin #1), and agentic knowledge work (GDPval-AA ELO 1500). For most general use, GPT-5.5. For legal/finance work or high-volume agentic tasks where cost matters, Grok 4.3.
Grok 4.3 costs published API rates for input and output tokens. GPT-5.5 costs published API rates for input and output. That makes Grok 4.3 roughly 4x cheaper on input and 12x cheaper on output. For high-volume workloads where output dominates the cost, Grok 4.3 can be 10x or more cheaper end-to-end.
xAI is positioning Grok 4.3 as a value play. Pricing was deliberately set to undercut OpenAI and Anthropic — input prices dropped 40% and output prices dropped 60% versus the previous Grok 4.20. Combined with reasoning being always-on (no separate reasoning tier), this brings the price of "1M context + reasoning" to roughly 1/12th of Claude Opus 4.7.
Independent evaluators (Vals AI, Andon Labs) report two real weaknesses. First, general coding — Grok 4.3 ranks 13th on broader coding benchmarks despite being strong in specific domains. Second, agent persistence: Andon Labs reports Grok 4.3 sometimes sits idle on autonomous tasks ("narcolepsy"), preferring to wait rather than act. For general software engineering or long-running unattended agents, GPT-5.5 is more reliable.
Three areas have clear independent confirmation. CaseLaw v2 (legal reasoning) — Grok 4.3 ranks #1 at 79.3% accuracy, a 25-point jump over Grok 4.20. CorpFin (corporate finance) — ranked #1. Real-world agentic knowledge work — Grok 4.3 scores ELO 1500 on GDPval-AA, a 321-point gain over its predecessor and ahead of Gemini 3.1 Pro. Always-on reasoning seems particularly suited to dense, structured domains.
Yes. MultipleChat AI gives you the latest API versions of ChatGPT, Claude, Gemini, Grok and Perplexity Sonar in one one paid subscription. Compare Mode runs them in parallel — useful for routing tasks to the cheaper model when quality is comparable, and falling back to the smarter flagship when it matters. AI Collaboration modes can also have one model verify another's work.
Note on benchmarks: All scores in this article are sourced from official launch announcements (xAI, OpenAI), independent benchmarking firms (Artificial Analysis, Vals AI, Andon Labs), and major tech press coverage as of May 2026. Where labs ran different methodologies on the same benchmark, scores may not be perfectly comparable — treat absolute numbers as directional. Pricing and model capabilities change frequently; verify current figures with each provider before making procurement decisions. MultipleChat AI does not guarantee the accuracy of third-party benchmark data and accepts no responsibility for decisions made based on this content.
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