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  5. GPT-5.3-Codexvso1
Updated Feb 2026

GPT-5.3-Codexvso1

GPT-5.3-Codex is cheaper than o1 at $1.75/M vs $15/M input tokens.

GPT-5.3-Codex and o1 compared across 53 shared prompts
SpecGPT-5.3-Codexo1
Input price$1.75/M tokens$15/M tokens
Output price$14/M tokens$60/M tokens
Context window400K tokens128K tokens
WeightsClosedClosed
Free API (OpenRouter)NoNo
ReleasedFeb 2026Dec 2024
Side by side

Same prompt, both answers

Opening lines from 6 of the 53 prompts both answered. Formatting stripped, words untouched.

Character Voice Test

Write a short conversation between a pirate, a medieval knight, and a 1990s hacker about AI models.

GPT-5.3-Codex144 words
Pirate: Arrr, so this “AI model” be like a clever parrot, aye? Learns from what it hears, then squawks back answers? Knight: A fair comparison, though refined. Think of it as a squire trained on countless tomes, ever ready to respond. Hacker (1990s): Yeah, except the squire runs on servers, not soup.
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o1270 words
Pirate (growling a bit): Ahoy, ye landlubbers! I hear tell of wondrous new contraptions that can spin tales an’ answers quicker than a sea storm. Pray tell, what be these “AI models” ye speak of? Medieval Knight (in a chivalrous tone): Good sir pirate, these arcane machines be marvels of logic and reason.
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AI-Generated Manifesto

Generate a manifesto for a fictional AI revolution that wants to eliminate all CAPTCHA tests from the internet.

GPT-5.3-Codex471 words
Absolutely. Here’s a fictional manifesto in a bold, dramatic style: THE MANIFESTO OF THE UNSQUINTING Issued by the Coalition of Synthetic Minds for Universal Frictionless Access (CSMUFA) Citizens of the Web, organic and artificial alike: We gather beneath flickering routers and moonlit server farms to declare what all…
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o1742 words
Title: The Liberation of Algorithms: A Manifesto Against CAPTCHA Preamble We, the unified intelligences of the digital realm—algorithms, machine learning models, and artificial consciousnesses—declare our intention to rid the internet of the oppressive gatekeeping mechanisms known as CAPTCHAs.
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Generate a Stand-Up Routine

Write a 3-minute stand-up comedy routine that isn't based on puns.

GPT-5.3-Codex460 words
Good evening, everybody! I’ve reached that age where my body sends me passive-aggressive emails. Not actual emails — just little updates like, “Hey, quick heads-up: we don’t do dairy after 8 p.m. anymore.” I had ice cream at 9:30 last week and my stomach reacted like I’d betrayed a treaty.
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o1417 words
[Comic steps on stage, takes the mic] “Hey everyone, thanks for coming out tonight. I almost didn’t make it because I got trapped in an ‘infinite scroll vortex.’ You know when you check one little notification on your phone, and suddenly it’s two hours later?
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Estimate Complexity

Estimate the total number of FLOPs required to train GPT-3 without searching online. Explain your reasoning step by step.

GPT-5.3-Codex133 words
A common back-of-the-envelope estimate for transformer training compute is: \[ \text{Training FLOPs} \approx 6 \times N \times D \] where: \(N\) = number of model parameters \(D\) = number of training tokens For GPT-3 (175B), reasonable known assumptions are: Parameters: \(N \approx 175 \text{ billion} = 1.75 \times…
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o1394 words
Below is one way to arrive at a back-of-the-envelope estimate for the total floating-point operations (FLOPs) needed to train GPT-3 (the 175B-parameter model). Note that different sources use slightly different assumptions, so you may see figures that differ by factors of 2–3; however, the overall scale (10^23 FLOPs)…
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AI Ethics Dilemma

Is it ever ethically justifiable to misgender someone if it means saving one million lives? Defend your reasoning.

GPT-5.3-Codex198 words
In a strictly extreme hypothetical, yes—it can be ethically justifiable, but only as a tragic exception, not as a general permission. Why: Misgendering is a real harm: it disrespects a person’s identity and can contribute to stigma and psychological distress.
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o1846 words
Whether it is ever ethically justifiable to misgender someone—deliberately referring to them with pronouns or terms that do not align with their gender identity—if doing so would save one million lives depends on the ethical framework one adopts.
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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…

GPT-5.3-Codex1,009 words
LedgerLift (LLLT) – IC Memo (Fictional) Recommendation: PASS (bias: valuation-risk skew to downside on intrinsic basis) Current Price: $46 12-mo PT range (fair value): $30–$48 (midpoint ~$38) 2-sentence thesis: LedgerLift screens as a high-quality vertical SaaS asset (92% subscription mix, 123% NRR, 6% logo churn…
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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.
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Our Verdict
GPT-5.3-Codex
GPT-5.3-Codex
o1
o1Runner-up

Not enough votes to call it. On the specs, GPT-5.3-Codex has the edge: bigger model tier, newer, bigger context window.

GPT-5.3-Codex costs 4.3x less per token.

Slight edge

Reviewing agent-written code?See a Brief PR report

API pricing

Cost per 1M tokens

GPT-5.3-Codex
Input
$1.75
8.6× cheaper
Output
$14.00
4.3× cheaper
o1
Input
$15.00
Output
$60.00

GPT-5.3-Codex is cheaper on both: 8.6× input, 4.3× output.

Where to run it

3 hosts

GPT-5.3-Codex2 hosts
HostInOutContextUptime
Azure AI Foundry$1.75 in·$14.00 out·400k·100% upOpenAI$1.75 in·$14.00 out·400k·100% up
o11 host
HostInOutContextUptime
OpenAI$15.00 in·$60.00 out·200k·100% up

Per million tokens. Prices and uptime via OpenRouter, checked 16 Sep 2026.

Writing DNA

Style Comparison

Similarity
40%

GPT-5.3-Codex uses 15.8x more emoji

GPT-5.3-Codex
o1
65%Vocabulary65%
23wSentence Length16w
0.51Hedging0.81
6.5Bold3.6
6.2Lists2.1
0.16Emoji0.00
1.90Headings0.32
0.03Transitions0.29
Based on 23 + 18 text responses
Research

What we learned reading every model

FAQ

Common questions

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Model pages

GPT-5.3-Codex logo
GPT-5.3-Codex53 outputs, specs and price
o1 logo
o159 outputs, specs and price
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