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  5. Claude Opus 5.5vso1
Updated Sep 2026

Claude Opus 5.5vso1

Claude Opus 5.5 is cheaper than o1 at $4/M vs $15/M input tokens.

Claude Opus 5.5 and o1 compared across 19 shared prompts
SpecClaude Opus 5.5o1
Input price$4/M tokens$15/M tokens
Output price$20/M tokens$60/M tokens
Context window1.0M tokens128K tokens
WeightsClosedClosed
Free API (OpenRouter)NoNo
ReleasedSep 2026Dec 2024
Side by side

Same prompt, both answers

Opening lines from 2 of the 19 prompts both answered. Formatting stripped, words untouched.

Advanced Investment Memo (IC Memo)

You are writing an internal investment committee memo for a long/short equity fund. Company (fictional): LedgerLift (ticker: LLLT) – B2B…

Claude Opus 5.51,335 words
IC Memo: LedgerLift (LLLT): Short, Starter Size, Hedged vs. Peer Basket Fictional exercise. Not investment advice. Recommendation Short (starter size, 1–1.5% gross), paired against a long basket of Peers A, B and C. 12-month price target range: $36–42 (current price $46, implying 9–22% downside). Thesis.
Read the full answer
o1820 words
RECOMMENDATION, PRICE TARGET, THESIS Recommendation: SHORT LedgerLift (LLLT). 12-month Price Target Range: $25–$35 (implying 25–45% downside). Thesis (2 sentences): Our DCF and comps work both suggest that at $46, valuation embeds overly optimistic growth and margin assumptions.
Read the full answer

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 $4.8m per year. Mezz PIK accrues to principal. All FCF after mandatory debt service sweeps to the TL.
Read the full answer
o11,012 words
Below is a self‐contained “quick‐and‐dirty” 5‐year LBO illustration for “HarborTech Services,” based strictly on the data given. All figures in US$ millions unless noted.
Read the full answer
Our Verdict
Claude Opus 5.5
Claude Opus 5.5
o1
o1Runner-up

Not enough votes to call it. On the specs, Claude Opus 5.5 has the edge: bigger model tier, newer, bigger context window.

Claude Opus 5.5 costs 3.0x less per token.

Slight edge

Reviewing agent-written code?See a Brief PR report

API pricing

Cost per 1M tokens

Claude Opus 5.5
Input
$4.00
3.8× cheaper
Output
$20.00
3.0× cheaper
o1
Input
$15.00
Output
$60.00

Claude Opus 5.5 is cheaper on both: 3.8× input, 3.0× output.

Where to run it

5 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
o11 host
HostInOutContextUptime
OpenAI$15.00 in·$60.00 out·200k·100% 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 o1 is developed by OpenAI. Claude Opus 5.5 has a 1.0M token context window vs o1's 128K. 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 o1 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 o1 costs $15/M input tokens. Claude Opus 5.5 is $11.00/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 o1 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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Model pages

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Claude Opus 5.519 outputs, specs and price
o1 logo
o159 outputs, specs and price
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