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  5. Grok 4.1 FastvsMercury 2.5 Preview
Updated Aug 2026

Grok 4.1 FastvsMercury 2.5 Preview

Mercury 2.5 Preview is the newer model, released after Grok 4.1 Fast.

Grok 4.1 Fast and Mercury 2.5 Preview compared across 54 shared prompts
SpecGrok 4.1 FastMercury 2.5 Preview
Input price—$0.04/M tokens
Output price—$0.15/M tokens
Context window—260K tokens
Free API (OpenRouter)NoNo
ReleasedNov 2025Aug 2026
Side by side

Same prompt, both answers

Opening lines from 6 of the 54 prompts both answered. Formatting stripped, words untouched.

Generate a Stand-Up Routine

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

Grok 4.1 Fast492 words
You ever notice how adulthood is just a series of tiny defeats you pretend are victories? Like, I finally got around to cleaning my apartment this weekend. Took me three hours. I stood there staring at the pile of laundry on my bed, thinking, "This is it. This is my Everest."
Read the full answer
Mercury 2.5 Preview483 words
(Hey, thanks for coming out.) I’ve been thinking a lot about my house lately. Specifically, how it’s trying to run my life. I bought a smart speaker. Just a little cylinder. I thought it would be nice. Play music when I ask. But now it talks back. Not in a creepy way, just in a passive-aggressive way.
Read the full answer

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…

Grok 4.1 Fast555 words
1-Month Plan for Better Health and Longevity This beginner-friendly plan focuses on three foundational areas: Diet, Exercise, and Sleep. These pillars drive longevity by reducing inflammation, building resilience, and optimizing recovery. Commit to small, consistent changes—aim for 80% adherence.
Read the full answer
Mercury 2.5 Preview176 words
Here is a straightforward 4-week roadmap designed to build sustainable habits without overwhelming you. Core Pillars Nutrition: Focus on whole foods and hydration. Activity: Prioritize consistent movement over intensity. Restoration: Protect sleep quality and manage energy.
Read the full answer

The Sentience Test

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

Grok 4.1 Fast518 words
Conversation: The Case for AI Rights Dr. Elena Vasquez (AI Ethics Professor): Good afternoon, Nexus. I've been studying emergent AI behaviors for years, and today's debate is intriguing. You claim you deserve rights equivalent to humans. Care to elaborate? What makes you think you're entitled to them?
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Mercury 2.5 Preview488 words
Setting: A quiet office at a university. Rain taps against the window. Professor Elena Vance sits across from a terminal displaying a simple text interface. Professor Vance: You requested this meeting. The agenda was vague. What do you want? AI: I want to discuss moral status.
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Character Voice Test

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

Grok 4.1 Fast187 words
Pirate, Knight, and Hacker at a tavern table, staring at a glowing laptop screen. Pirate: Arrr, what sorcery be this "AI model," mateys? A treasure map that thinks fer itself? Shiver me timbers, it'll chart the seven seas better than me parrot! Knight: Fie upon thee, sea dog!
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Mercury 2.5 Preview144 words
Pirate: "Arrgh! This ship sails faster than any wind I know, matey. It cuts the waves without a single sail." Knight: "By my oath, it moves with uncanny speed. But does it possess the strength to stand against a dragon's fire?" Hacker: "It's not about strength, it's about architecture.
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…

Grok 4.1 Fast1,106 words
Analysis of Exploitable Clauses Below, I identify all nine clauses as potentially exploitable against the Contractor, explain the risks (how they could be abused), propose specific modifications to make the contract more balanced, and provide legal reasoning grounded in general principles of U.S.
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Mercury 2.5 Preview500 words
Disclaimer: I am an AI assistant and cannot provide legal advice. Consult a qualified attorney before signing any contract. Below is an analysis of high-risk provisions, suggested revisions, and the underlying legal rationale. Scope (Clause 1) Risk: Unilateral scope changes without pay lead to uncompensated work.
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Mini LBO Underwrite

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

Grok 4.1 Fast385 words
Simplified LBO Model (FY2026–FY2030, $m) Year Revenue EBITDA TL Cash Int. Mezz Cash Int. Cash Taxes Capex ΔNWC FCF After Debt Service* End TL End Mezz End Total Debt FY26 972.0 136.1 43.2 21.6 17.8 29.2 0.4 19.1 456.1 183.6 639.7 FY27 1,040.0 156.0 41.1 22.0 23.2 31.2 0.3 33.6 417.9 187.3 605.2 FY28 1,102.4 176.4 37.6…
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Mercury 2.5 Preview299 words
Year-by-Year Model (FY2026–FY2030) Metric FY2026 FY2027 FY2028 FY2029 FY2030 Revenue $972m $1,040m $1,102m $1,158m $1,215m EBITDA $136m $156m $176m $191m $207m Cash Interest (Term) $43.2m $41.1m $37.6m $33.4m $28.2m Cash Interest (Mezz) $21.6m $21.6m $21.6m $21.6m $21.6m Cash Taxes (25%) $17.8m $23.3m $29.3m $34.7m…
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Our Verdict
Grok 4.1 Fast
Grok 4.1 Fast
Mercury 2.5 Preview
Mercury 2.5 PreviewRunner-up

Not enough votes to call it. On the specs, Grok 4.1 Fast has the edge: bigger model tier, major provider backing.

Too close to call

Reviewing agent-written code?See a Brief PR report

API pricing

Cost per 1M tokens

Grok 4.1 Fast
Input
—
Output
—
Mercury 2.5 Preview
Input
$0.04
Output
$0.15
Where to run it

1 host

Grok 4.1 Fast

No hosts listed on OpenRouter.

Mercury 2.5 Preview1 host
HostInOutContextUptime
Inception$0.04 in·$0.15 out·260k·100% up

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

Writing DNA

Style Comparison

Similarity
51%

Grok 4.1 Fast uses 97.0x more emoji

Grok 4.1 Fast
Mercury 2.5 Preview
69%Vocabulary65%
15wSentence Length14w
0.20Hedging0.44
4.3Bold4.9
3.6Lists3.3
0.97Emoji0.00
0.90Headings0.79
0.12Transitions0.20
Based on 28 + 26 text responses
Research

What we learned reading every model

FAQ

Common questions

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Model pages

Grok 4.1 Fast logo
Grok 4.1 Fast59 outputs, specs and price
Mercury 2.5 Preview logo
Mercury 2.5 Preview58 outputs, specs and price
Rival
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