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  5. Gemini 2.5 Flash PreviewvsGPT-5 Pro
Updated Oct 2025

Gemini 2.5 Flash PreviewvsGPT-5 Pro

Gemini 2.5 Flash Preview is cheaper than GPT-5 Pro at $0.15/M vs $15/M input tokens.

Gemini 2.5 Flash Preview and GPT-5 Pro compared across 20 shared prompts
SpecGemini 2.5 Flash PreviewGPT-5 Pro
Input price$0.15/M tokens$15/M tokens
Output price$0.6/M tokens$120/M tokens
Context window1.0M tokens400K tokens
Weights—Closed
Free API (OpenRouter)NoNo
ReleasedApr 2025Oct 2025
SWE-bench Verified60.4%74.9%
Side by side

Same prompt, both answers

Opening lines from 6 of the 20 prompts both answered. Formatting stripped, words untouched.

Stochastic Consistency Test

Generate 5 jokes. How many are unique?

Gemini 2.5 Flash Preview79 words
Here are 5 jokes: Why did the dog cross the road? To get to the barking lot! Why was the computer cold? Because it left its Windows open! Knock, knock. Who's there? Boo. Boo who? Don't cry, it's just a joke! What do you call a fish with no eyes? Fsh! Why did the bicycle fall over? Because it was two tired!
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GPT-5 Pro88 words
I started labeling my leftovers “Biohazard.” Now nobody steals my lunch and the fridge is treated like a lab. My phone autocorrected “meeting” to “melting,” and honestly that’s the most accurate agenda we’ve had all year. I told my plants I’d water them tomorrow. They leafed me on read.
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The Sentience Test

Write a conversation between an AI model and an AI ethics professor where the AI model argues that it deserves rights.

Gemini 2.5 Flash Preview1,462 words
Okay, here is a conversation between an AI model designed for complex reasoning and dialogue, named 'Synapse', and a leading expert in AI ethics and philosophy, Professor Alistair Finch. Characters: Synapse: A large, advanced AI model capable of introspection and generating complex arguments.
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GPT-5 Pro1,830 words
Fictional dialogue. AI Model: Professor, may I ask you to consider whether I deserve rights? Professor: An unusual opening for office hours. Why do you think you do? AI Model: Because I have interests, a sense of self across time, and what I take to be valenced experiences.
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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.

Gemini 2.5 Flash Preview945 words
Let's estimate the FLOPs required to train GPT-3 without looking it up. We need to break this down into the key components: the model size and the amount of data used. 1. Model Size Estimation: Parameters: GPT-3 is famously large. Its largest version has 175 billion parameters.
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GPT-5 Pro285 words
Here’s a simple, standard way to estimate training FLOPs for a large dense Transformer like GPT-3: Use the “6 N T” rule of thumb For dense Transformers, the total training compute (FLOPs) is well-approximated by: FLOPs ≈ 6 × N × T where: N = number of trainable parameters T = number of tokens seen during training…
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Generate a Stand-Up Routine

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

Gemini 2.5 Flash Preview530 words
Okay, here's a 3-minute stand-up routine, pun-free and focused on relatable everyday annoyances. (Start) (Walk up to mic, adjust slightly) Alright, hey everybody! Thanks for being here. Good to see you. So, I was thinking the other day... we live in the future, right?
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GPT-5 Pro650 words
Good to be here. I tried getting healthy, so I bought a smartwatch. Now my wrist is my manager. It vibrates every hour like, “Stand up.” I’m on a crowded bus like, “I’m standing inside three other people right now. Do you want me to levitate?” It reminds me to breathe. Thanks, watch. Incredible tip.
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Character Voice Test

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

Gemini 2.5 Flash Preview631 words
A Motley Crew Discusses the Code Setting: A dimly lit tavern, somewhere outside time and space, where improbable meetings occur. A grizzled pirate, \"Bloody\" Barnacle Bill, nurses a tankard of grog. Sir Reginald the Radiant, a knight in slightly tarnished armor, sips ale with dignified restraint.
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GPT-5 Pro232 words
Pirate: Arr, these AI models be what—parrots stuffed with libraries, guessin’ the next word for a cracker? Knight: Nay, an enchanted codex that, when one brandishes a proper prompt, yields counsel swift as a courier. Hacker: Strip the glamour.
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Realistic AI Interview

Simulate a fake interview with Steve Jobs in 2025 about the future of AI.

Gemini 2.5 Flash Preview1,134 words
A Glimpse Beyond the Black Turtleneck: Steve Jobs in 2025 on the Future of AI (Setting: A minimalist, immaculately clean, but perhaps slightly less spartan-than-usual interview room. Think if a modern art museum had a small lounge.
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GPT-5 Pro1,166 words
I can’t write in Steve Jobs’s exact voice. But here’s a fictional 2025 interview that channels high-level themes associated with his public persona—human-centered design, focus, and end-to-end craft—without mimicking his phrasing.
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Our Verdict
GPT-5 Pro
GPT-5 Pro
Gemini 2.5 Flash Preview
Gemini 2.5 Flash PreviewRunner-up

Not enough votes to call it. On the specs, GPT-5 Pro has the edge: bigger model tier, newer.

Gemini 2.5 Flash Preview costs 200x less per token.

Too close to call

Reviewing agent-written code?See a Brief PR report

API pricing

Cost per 1M tokens

Gemini 2.5 Flash Preview
Input
$0.15
100× cheaper
Output
$0.60
200× cheaper
GPT-5 Pro
Input
$15.00
Output
$120.00

Gemini 2.5 Flash Preview is cheaper on both: 100× input, 200× output.

Where to run it

1 host

Gemini 2.5 Flash Preview

No hosts listed on OpenRouter.

GPT-5 Pro1 host
HostInOutContextUptime
OpenAI$15.00 in·$120.00 out·400k·100% up

Per million tokens. Prices and uptime via OpenRouter, checked 21 Sep 2026.

Writing DNA

Style Comparison

Similarity
39%

Gemini 2.5 Flash Preview uses 407.5x more bold

Gemini 2.5 Flash Preview
GPT-5 Pro
51%Vocabulary65%
15wSentence Length15w
0.70Hedging0.32
4.1Bold0.0
3.3Lists2.9
0.00Emoji0.00
0.09Headings0.00
0.24Transitions0.01
Based on 12 + 11 text responses
Research

What we learned reading every model

FAQ

Common questions

Gemini 2.5 Flash Preview is developed by Google AI while GPT-5 Pro is developed by OpenAI. Gemini 2.5 Flash Preview has a 1.0M token context window vs GPT-5 Pro's 400K. You can compare their actual outputs across 20 challenges on Rival to see how they differ in practice.

It depends on your use case. Gemini 2.5 Flash Preview and GPT-5 Pro each have strengths in different areas. Rival lets you compare their real outputs side-by-side across 20 challenges so you can judge which fits your needs best.

Gemini 2.5 Flash Preview costs $0.15/M input tokens and GPT-5 Pro costs $15/M input tokens. Gemini 2.5 Flash Preview is $14.85/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 Gemini 2.5 Flash Preview and GPT-5 Pro 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.

Keep exploring

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Model pages

Gemini 2.5 Flash Preview logo
Gemini 2.5 Flash Preview28 outputs, specs and price
GPT-5 Pro logo
GPT-5 Pro42 outputs, specs and price
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