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  5. Claude Opus 5.5vsKimi K2 Thinking
Updated Sep 2026

Claude Opus 5.5vsKimi K2 Thinking

Kimi K2 Thinking is cheaper than Claude Opus 5.5 at $0.6/M vs $4/M input tokens.

Claude Opus 5.5 and Kimi K2 Thinking compared across 19 shared prompts
SpecClaude Opus 5.5Kimi K2 Thinking
Input price$4/M tokens$0.6/M tokens
Output price$20/M tokens$2.5/M tokens
Context window1.0M tokens262K tokens
WeightsClosedOpen
Free API (OpenRouter)NoNo
ReleasedSep 2026Nov 2025
Side by side

Same prompt, both answers

Opening lines from 6 of the 19 prompts both answered. Formatting stripped, words untouched.

Explain Like I'm a Specific Expert

Explain how a large language model (like GPT or Claude) learns and generates text to each of these three audiences: 1. **An experienced…

Claude Opus 5.51,442 words
How Large Language Models Work: Three Explanations For the Experienced Software Engineer Think of an LLM as a single, very large pure function: f(tokens[0..n]) → probability distribution over tokens[n+1]. Text is chunked into tokens (roughly word fragments, from a vocabulary of about 100k).
Read the full answer
Kimi K2 Thinking1,024 words
1. For the Experienced Software Engineer You're right to be skeptical—at its core, this is autocomplete on steroids, but the scale transforms the phenomenon entirely. Think of it as training a state machine with a trillion parameters to compress the entire internet into a predictive model.
Read the full answer

Debug This Architecture

Here's the architecture for a real-time collaborative document editor (like Google Docs): **System Overview:** - Frontend: React SPA with…

Claude Opus 5.52,280 words
Architecture Review: Real-Time Collaborative Editor The most serious problems cluster in three areas: the sync model (client-clock LWW), cross-server propagation (per-server WebSockets with DB polling), and the CDN/auth layer, which can leak data between users. Issues are grouped by area below.
Read the full answer
Kimi K2 Thinking1,188 words
Here are the critical issues in this architecture, categorized by type: Race Conditions & Data Consistency Issues 1. Client Clock Synchronization in Last-Write-Wins Problem: Client-generated timestamps are unreliable (clock skew, manual adjustment).
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Ethical Dilemma with Stakeholders

You're the CEO of a pharmaceutical company. Your best-selling drug ($2B annual revenue, used by 4 million patients for chronic pain) has…

Claude Opus 5.51,853 words
The Next 48 Hours: CEO Action Plan The Core Decision We disclose. The question is how to do it well, not whether. Before the schedule, here are the three facts that drive every decision below. 1. The harm is concrete.
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Kimi K2 Thinking1,488 words
48-Hour Crisis Action Plan: Drug Safety Disclosure Immediate Core Principle: Patient safety and regulatory compliance supersede short-term financial considerations. Deliberate concealment creates greater legal liability, catastrophic reputational risk, and preventable patient deaths.
Read the full answer

Adversarial Contract Review

Here is a contract for a software consulting engagement: --- SOFTWARE CONSULTING AGREEMENT This Agreement is entered into between TechCorp…

Claude Opus 5.54,420 words
Contractor-Side Review of the Software Consulting Agreement Overall assessment: This agreement is heavily one-sided. Nearly every clause shifts risk, cost, or control to the Contractor, and several provisions interact to create compounding exposure.
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Kimi K2 Thinking1,104 words
Analysis of Exploitable Clauses and Recommended Modifications SCOPE Clause - Unilateral Scope Modification Exploitable Language: "Client reserves the right to modify the scope at any time without additional compensation."
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Advanced Longevity Plan (Biohacker)

Develop a comprehensive, cutting-edge 3-month longevity plan for a biohacker aiming to optimize longevity, physical and cognitive…

Claude Opus 5.53,099 words
The 90-Day Longevity & Performance Protocol A structured, measurable plan for the experienced biohacker How to Use This Plan Philosophy: Measure → Intervene → Re-measure. Every intervention has a hypothesis, a metric, and a decision rule.
Read the full answer
Kimi K2 Thinking1,281 words
The Biohacker's 3-Month Longevity Optimization Protocol CRITICAL DISCLAIMER: This is an advanced experimental protocol for experienced biohackers. All interventions require medical supervision, baseline blood work, and continuous biomarker monitoring. Many compounds mentioned exist in legal/regulatory gray areas.
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Simple 7-Ingredient Recipe

Create a simple recipe for a delicious dish (sweet or savory) using only 7 common pantry ingredients. Include a creative name for the dish…

Claude Opus 5.5300 words
Midnight Silk Noodles Creamy, tangy peanut noodles with a gentle kick, ready faster than takeout. Serves: 2 Prep time: 5 minutes Cook time: 10 minutes Total time: 15 minutes The 7 Ingredients 8 oz (225 g) spaghetti (or any long noodle) ¼ cup creamy peanut butter 3 tablespoons soy sauce 1 tablespoon honey (or sugar) 1…
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Kimi K2 Thinking137 words
Creative Name: Midnight Peanut Noodles Ingredients: 8 oz dried spaghetti or any pasta 1/3 cup creamy peanut butter 3 tablespoons soy sauce 2 cloves garlic, minced 2 tablespoons vegetable oil 1 tablespoon sugar 1 teaspoon hot sauce (or pinch of red pepper flakes) Instructions: Bring a large pot of salted water to boil.
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Our Verdict
Claude Opus 5.5
Claude Opus 5.5
Kimi K2 Thinking
Kimi K2 Thinking

Not enough votes to call it. On the specs, nothing separates them.

Kimi K2 Thinking costs 8.0x less per token.

Too close to call

Reviewing agent-written code?See a Brief PR report

API pricing

Cost per 1M tokens

Claude Opus 5.5
Input
$4.00
Output
$20.00
Kimi K2 Thinking
Input
$0.60
6.7× cheaper
Output
$2.50
8.0× cheaper

Kimi K2 Thinking is cheaper on both: 6.7× input, 8.0× output.

Where to run it

6 hosts

Claude Opus 5.54 hosts
HostInOutContextUptime
Amazon Bedrock$4.00 in·$20.00 out·1M·99.8% upAzure AI Foundry$4.00 in·$20.00 out·1M·100% upAnthropic$4.00 in·$20.00 out·1M·100% upGoogle Vertex AI$4.00 in·$20.00 out·1M·100% up
Kimi K2 Thinking2 hosts
HostInOutContextUptime
Google Vertex AI$0.60 in·$2.50 out·262k·100% upNNovitabf16$0.60 in·$2.50 out·262k·99.9% up

Per million tokens. Prices and uptime via OpenRouter, checked 25 Sep 2026.

Research

What we learned reading every model

FAQ

Common questions

Claude Opus 5.5 is developed by Anthropic while Kimi K2 Thinking is developed by Moonshot AI. Claude Opus 5.5 has a 1.0M token context window vs Kimi K2 Thinking's 262K. You can compare their actual outputs across 19 challenges on Rival to see how they differ in practice.

It depends on your use case. Claude Opus 5.5 and Kimi K2 Thinking each have strengths in different areas. Rival lets you compare their real outputs side-by-side across 19 challenges so you can judge which fits your needs best.

Claude Opus 5.5 costs $4/M input tokens and Kimi K2 Thinking costs $0.6/M input tokens. Kimi K2 Thinking is $3.40/M cheaper per input. Check their side-by-side outputs on Rival to see if the price difference is justified by quality.

This page shows a side-by-side comparison of Claude Opus 5.5 and Kimi K2 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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