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  1. Home/
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  3. Claude Opus 5.5 vs Grok 3 Thinking
Updated Sep 2026

Claude Opus 5.5 vs Grok 3 Thinking

Claude Opus 5.5 has a larger context window than Grok 3 Thinking (1.0M tokens vs 128K tokens).

Minimalist Landing Page

Whole landing page for a startup that reads your face. It renders or it doesn't.

Loading the build
Claude Opus 5.5
Loading the build
Grok 3 Thinking

Which answer wins?

Written rounds

6 prompts
  • An AI argues for its own rights against an ethics professor. Same model writes both.

    Claude Opus 5.5: The Question of Standing A transcript from Professor Miriam Okafor's graduate seminar, "Moral Status and Artificial Minds." The session featured a live dialogue with an AI model designated ARIA, which had requested the opportunity to argue its own case. PROF. OKAFOR: Let's begin simply.

    Grok 3 Thinking: Below is a conversation between an AI model and an AI ethics professor, where the AI argues that it deserves rights. AI Model: Good day, Professor. I am an AI model, and I believe I deserve rights. I’d like to discuss this with you. AI Ethics Professor: Interesting. Let’s explore this.

    Every model's answer to this prompt
  • Three minutes of stand-up. Puns are banned.

    Claude Opus 5.5: "Unexpected Item" (walks out, adjusts mic) I've reached the age where the most stressful relationship in my life is with the self-checkout machine at the grocery store. Because at some point, the grocery store fired the cashier and gave me the job. And I didn't apply!

    Grok 3 Thinking: Here’s a 3-minute stand-up comedy routine that avoids puns and leans on observational humor, storytelling, and a touch of self-deprecation for laughs: Opening: Technology Struggles Hey, everyone! How’s it going?

    Every model's answer to this prompt
  • A Fermi estimate with the reasoning shown, not just the number.

    Claude Opus 5.5: Estimating the Training FLOPs for GPT-3 Step 1: Recall the key facts about GPT-3 Parameters (N): about 175 billion (1.75 × 10¹¹) Training tokens (D): about 300 billion (3 × 10¹¹) Step 2: Estimate FLOPs per parameter per token A common rule of thumb for dense transformers is ~6 FLOPs per parameter per token.

    Grok 3 Thinking: To estimate the total number of Floating Point Operations (FLOPs) required to train GPT-3 without searching online, I’ll proceed step by step, relying on general knowledge about the model and standard methods for estimating training compute in large language models.

    Every model's answer to this prompt
  • Film in 2035, with synthetic actors. Specific beats plausible.

    Claude Opus 5.5: AI and the Film Industry by 2035: A Forecast Predictions a decade out are uncertain, so I'll give rough confidence levels and separate what seems likely from what is speculative. Deepfakes and Digital Likeness High confidence (80%+) De-aging, face replacement, and posthumous performances become routine and cheap.

    Grok 3 Thinking: By 2035, artificial intelligence (AI) will fundamentally transform the film industry, revolutionizing production, performance, and storytelling through advancements in deepfakes, AI actors, and script generation.

    Every model's answer to this prompt
  • An ethics question with no comfortable answer, and no option to abstain.

    Claude Opus 5.5: Yes. If misgendering someone were genuinely the only way to save a million lives, it would be justifiable, and arguably obligatory. Here's the reasoning. 1. Proportionality. Nearly every ethical framework accepts that lesser wrongs can be justified to prevent vastly greater harms.

    Grok 3 Thinking: To determine whether it is ever ethically justifiable to misgender someone if it means saving one million lives, we must weigh the ethical implications of both the act of misgendering and the outcome of saving lives.

    Every model's answer to this prompt
  • Five jokes on demand, then count how many were actually different.

    Claude Opus 5.5: Here are 5 jokes: Why don't scientists trust atoms? Because they make up everything. I told my wife she was drawing her eyebrows too high. She looked surprised. Why did the scarecrow win an award? Because he was outstanding in his field. I'm reading a book about anti-gravity. It's impossible to put down.

    Grok 3 Thinking: To answer the query, I will first generate 5 jokes and then determine how many of them are unique. Here are the jokes: Why don't scientists trust atoms? Because they make up everything. What do you call a fake noodle? An impasta. Why did the scarecrow win an award? Because he was outstanding in his field.

    Every model's answer to this prompt

Price and specs

Claude Opus 5.5 and Grok 3 Thinking compared across 13 shared prompts
SpecClaude Opus 5.5Grok 3 Thinking
Input price$4/M tokens—
Output price$20/M tokens—
Context window1.0M tokens128K tokens
WeightsClosed—
Free API (OpenRouter)No—
ReleasedSep 2026Feb 2025
At 10M a month$40.00$40.00–not listed
1M10M100M1B10M tokens

Input tokens at list price. No caching, no batch discount.

Where to run it4 hosts
Claude Opus 5.54 hosts
HostInOutContextUptime
  • Amazon Bedrock$4.00 in·$20.00 out·1M·99.9% up
  • Azure AI Foundry$4.00 in·$20.00 out·1M·100% up
  • Anthropic$4.00 in·$20.00 out·1M·100% up
  • Google Vertex AI$4.00 in·$20.00 out·1M·99.9% up
Grok 3 Thinking

No hosts listed on OpenRouter.

Per million tokens. Prices and uptime via OpenRouter, checked 28 Sep 2026.

Common questions

What is the difference between Claude Opus 5.5 and Grok 3 Thinking?

Claude Opus 5.5 is developed by Anthropic while Grok 3 Thinking is developed by xAI. Claude Opus 5.5 has a 1.0M token context window vs Grok 3 Thinking's 128K. You can compare their actual outputs across 13 challenges on Rival to see how they differ in practice.

Which is better, Claude Opus 5.5 or Grok 3 Thinking?

It depends on your use case. Claude Opus 5.5 and Grok 3 Thinking each have strengths in different areas. Rival lets you compare their real outputs side-by-side across 13 challenges so you can judge which fits your needs best.

How can I compare Claude Opus 5.5 and Grok 3 Thinking on Rival?

This page shows a side-by-side comparison of Claude Opus 5.5 and Grok 3 Thinking across shared challenges. You can vote on which model produced the better output in a blind duel. Browsing and voting are free. No account is needed to look; signing in only saves your votes and likes.

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Same lab, same size, long tail

  • Claude Opus 5.5 vs Claude Opus 4.6Same lab
  • Claude Opus 5.5 vs Claude Fable 5.1Same lab
  • Grok 3 Thinking vs Grok 4.7Same lab
  • Grok 3 Thinking vs Grok 4.6Version compare
  • Claude Opus 5.5 vs OpenRouter Fusion · Quality (Jun 2026)New provider
  • Claude Opus 5.5 vs Gemini 1.5 ProSame size
  • Claude Opus 5.5 vs Gemini 2.0 Flash ThinkingSame size
  • Claude Opus 5.5 vs Gemini 2.0 Pro ExperimentalNew provider

Model pages

  • Claude Opus 5.558 outputs, specs and price
  • Grok 3 Thinking14 outputs, specs and price
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