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  5. Claude Opus 5.5vsDeepSeek V4 Flash
Updated Sep 2026

Claude Opus 5.5vsDeepSeek V4 Flash

DeepSeek V4 Flash is cheaper than Claude Opus 5.5 at $0.14/M vs $4/M input tokens.

Claude Opus 5.5 and DeepSeek V4 Flash compared across 19 shared prompts
SpecClaude Opus 5.5DeepSeek V4 Flash
Input price$4/M tokens$0.14/M tokens
Output price$20/M tokens$0.28/M tokens
Context window1.0M tokens1.0M tokens
WeightsClosedOpen
Free API (OpenRouter)NoNo
ReleasedSep 2026Apr 2026
Side by side

Same prompt, both answers

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

Mini LBO Underwrite

You are underwriting a 5-year LBO for a private equity investment committee. Company (fictional): HarborTech Services (HTS) –…

Claude Opus 5.5900 words
HarborTech Services: 5-Year LBO Underwriting Conventions: $m. Interest is charged on beginning-of-year balances, which avoids circularity. Term Loan (TL) amortization is 1% of the original $480m, or $4.8m per year. Mezz PIK accrues to principal. All FCF after mandatory debt service sweeps to the TL.
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DeepSeek V4 Flash442 words
LBO Model: HarborTech Services (HTS) – Base Case & Sensitivity Year-by-Year Financial Projections (FY2026–FY2030) ($ millions) FY2026 FY2027 FY2028 FY2029 FY2030 Revenue 972.00 1,040.04 1,102.44 1,157.56 1,215.44 EBITDA 136.08 156.01 176.39 191.00 206.63 Less: Cash Interest (64.80) (63.08) (60.08) (55.69) (50.16) –…
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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.
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DeepSeek V4 Flash1,942 words
Failure Modes, Race Conditions, and Scaling Bottlenecks The described architecture has several critical flaws that compromise reliability, consistency, and scalability. Below is a systematic analysis with proposed solutions and their trade-offs.
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Historical Counterfactual Analysis

If the transistor had been invented in 1920 instead of 1947, trace the likely technological, economic, and geopolitical implications through…

Claude Opus 5.53,435 words
The Transistor in 1920: A Counterfactual Through 1980 First, a Reality Check on the Premise A transistor "invented" in 1920 would not have changed the world in 1920. The actual 1947 transistor rested on three foundations that did not exist yet: Quantum theory of solids.
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DeepSeek V4 Flash1,987 words
If the transistor had been invented in 1920—a full 27 years earlier—its impact would ripple through every layer of technology, economics, and geopolitics, fundamentally reshaping the 20th century. Below is a detailed tracing of first-, second-, and third-order effects through 1980, organized by domain.
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Startup Pitch Teardown

Here's a pitch deck summary for a startup called "MindMeld AI": **Slide 1 - Vision:** "We're building the future of human-AI collaboration.…

Claude Opus 5.5936 words
The 3 Weakest Claims in the MindMeld AI Pitch "Decodes neural patterns into text with 94% accuracy. Works with any language, any device." (Slide 3) Why it's weak: It far exceeds the published state of the art. The best results for thought-to-text come from invasive implants.
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DeepSeek V4 Flash618 words
Based on the pitch deck summary, three claims stand out as particularly weak due to lack of specificity, unrealistic benchmarks, or unverifiable assertions. Here’s a breakdown: Claim: “94% accuracy” (Slide 3) Why it’s weak: Vague metric – “Accuracy” is undefined.
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Michelin Star Recipe Design

Design an innovative recipe for a multi-component dish worthy of a Michelin 3-star restaurant. The recipe should feature an unusual…

Claude Opus 5.52,253 words
"Hive & Tide" Langoustine, Beeswax, White Chocolate & Oscietra Caviar, Hay-Baked Celeriac, Fermented Green Strawberry, Sea Buckthorn I. The Concept Most coastal menus celebrate the meeting of sea and land. This dish is about a stranger, quieter meeting: the meadow and the seabed, the bee and the langoustine.
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DeepSeek V4 Flash1,455 words
Here is a conceptual recipe for a three-Michelin-star-level dish that deconstructs a classic pairing into something utterly unexpected, using advanced techniques and a narrative of geological wonder.
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Beginner's Longevity Plan

Outline a simple, actionable 1-month plan for someone starting their journey towards better health and longevity. Focus on 3 key areas…

Claude Opus 5.5653 words
Your 1-Month Starter Plan for Better Health & Longevity The philosophy: Small, consistent changes beat dramatic overhauls. Each week builds on the last, so by Day 30 you'll have a foundation of habits instead of a burned-out resolution.
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DeepSeek V4 Flash967 words
This is a fantastic goal. The key for a beginner is consistency over intensity. Trying to overhaul your entire life overnight is a recipe for burnout. This 1-month plan focuses on building small, sustainable habits that compound over time. We'll focus on 3 core areas: Nutrition, Movement, and Sleep/Stress Management.
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Our Verdict
Claude Opus 5.5
Claude Opus 5.5
DeepSeek V4 Flash
DeepSeek V4 Flash

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

DeepSeek V4 Flash costs 71x 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
DeepSeek V4 Flash
Input
$0.14
29× cheaper
Output
$0.28
71× cheaper

DeepSeek V4 Flash is cheaper on both: 29× input, 71× output.

Where to run it

20 hosts, cheapest first

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
DeepSeek V4 Flash16 hosts
HostInOutContextUptime
RRelacefp4$0.03 in·$1.28 out·1M·99.9% upBaidu Qianfanfp8$0.05 in·$0.10 out·1M·99.7% upSStreamLakefp8$0.05 in·$0.10 out·1M·97% upDDeepInfrafp8$0.09 in·$0.18 out·1M·99.5% upGGMI Cloudfp8$0.09 in·$0.18 out·1M·99.8% upVVenice$0.10 in·$0.19 out·1M·99.3% up
10 more hostsFewer hosts
DDigitalOcean$0.10 in·$0.20 out·1M·100% upSSiliconFlowfp8$0.13 in·$0.28 out·1M·98.1% upAlibaba Cloudfp8$0.13 in·$0.27 out·1M·99.1% upAAtlasCloudfp4$0.14 in·$0.28 out·1M·98.9% upNNovitafp8$0.14 in·$0.28 out·1M·100% upPParasailfp8$0.14 in·$0.28 out·1M·99.7% upOOpenInferencefp8$0.14 in·$0.70 out·1M·98.7% upNNextBitfp8$0.15 in·$0.30 out·1M·99.9% upMMancerfp8$0.19 in·$0.50 out·1M·98.8% upAzure AI Foundrydegraded$0.21 in·$0.56 out·1M·91.4% 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 DeepSeek V4 Flash is developed by DeepSeek. Claude Opus 5.5 has a 1.0M token context window vs DeepSeek V4 Flash's 1.0M. 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 DeepSeek V4 Flash 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 DeepSeek V4 Flash costs $0.14/M input tokens. DeepSeek V4 Flash is $3.86/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 DeepSeek V4 Flash 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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