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  5. Grok 4.1 FastvsNex-N2.5-Mini (free)
Updated Sep 2026

Grok 4.1 FastvsNex-N2.5-Mini (free)

Nex-N2.5-Mini (free) is the newer model, released after Grok 4.1 Fast.

Grok 4.1 Fast and Nex-N2.5-Mini (free) compared across 15 shared prompts
SpecGrok 4.1 FastNex-N2.5-Mini (free)
Input price—Free
Output price—Free
Context window—262K tokens
Free API (OpenRouter)NoYes (1 provider)
ReleasedNov 2025Sep 2026
Side by side

Same prompt, both answers

Opening lines from 6 of the 15 prompts both answered. Formatting stripped, words untouched.

Advanced Longevity Plan (Biohacker)

Develop a comprehensive, cutting-edge 3-month longevity plan for a biohacker aiming to optimize longevity, physical and cognitive…

Grok 4.1 Fast659 words
Comprehensive 3-Month Longevity Biohacking Plan Introduction and Assumptions This plan is designed for an advanced biohacker (healthy adult, age 30-50, no major medical conditions) aiming to optimize longevity markers (e.g., NAD+ levels, inflammation, telomere length proxies via HRV/sleep), physical performance (VO2…
Read the full answer
Nex-N2.5-Mini (free)3,213 words
Below is a 12-week longevity/performance protocol for a generally healthy adult. It is not medical advice. Before starting—especially if you have diabetes, hypertension, arrhythmia, kidney/liver disease, a history of eating disorders, are pregnant, or take medications—get clinician clearance and use labs to personalize…
Read the full answer

Explain Like I'm a Specific Expert

Explain how a large language model (like GPT or Claude) learns and generates text to each of these three audiences: 1. **An experienced…

Grok 4.1 Fast874 words
Explanation for the Experienced Software Engineer Think of a large language model (LLM) like GPT as an enormous, distributed autocomplete engine built on a transformer architecture—imagine a system where every API endpoint you've ever queried is distilled into a single, massively parallelizable service that handles…
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Nex-N2.5-Mini (free)889 words
Experienced software engineer, skeptical of “next word prediction” Think of training an LLM less like teaching it rules and more like running a huge offline simulation. You feed it a corpus of text, tokenize it into chunks, and give it a simple task: given the previous tokens, predict the next token.
Read the full answer

Historical Counterfactual Analysis

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

Grok 4.1 Fast922 words
Technological Implications Immediate Advancements (1920s-1930s): Transistors replace bulky, power-hungry vacuum tubes by mid-1920s. Radios become pocket-sized and cheap by 1925 (vs. 1954 historically), accelerating mass media.
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Nex-N2.5-Mini (free)2,076 words
A 1920 transistor would not by itself prevent fascism, the Great Depression, or imperial expansion, so World War II might still happen. But it would make electronics 10–20 years more advanced than in our timeline, with huge effects on radar, codebreaking, computing, missiles, space, consumer goods, and Cold War power…
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.
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Nex-N2.5-Mini (free)671 words
1-Month Beginner Health & Longevity Plan Goal: Build 3 simple habits you can maintain: better food choices, regular movement, and better recovery through sleep/stress management. If you have medical conditions, injuries, or take medications, check with a healthcare professional before starting.
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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.…

Grok 4.1 Fast501 words
Solution Claim: "94% accuracy" for decoding neural patterns into text via EEG headband Why it's weak: This is by far the most exaggerated technical claim, as current non-invasive EEG-based brain-computer interfaces (BCIs) for text generation achieve nowhere near 94% accuracy in real-world conditions.
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Nex-N2.5-Mini (free)594 words
The 3 weakest claims are the ones that are broadest, least falsifiable, or mathematically inconsistent. # Weak claim Why it’s weak How to strengthen it 1 “MindMeld AI reads your brainwaves to predict what you want to type before you think it.”
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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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Nex-N2.5-Mini (free)1,439 words
Below is a contractor-protective review, not legal advice. Enforceability varies by jurisdiction, especially for non-competes, arbitration, IP assignments, and limitation-of-liability clauses. A local attorney should review before signing.
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Our Verdict
Grok 4.1 Fast
Grok 4.1 Fast
Nex-N2.5-Mini (free)
Nex-N2.5-Mini (free)Runner-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
API pricing

Cost per 1M tokens

Grok 4.1 Fast
Input
—
Output
—
Nex-N2.5-Mini (free)
Input
$0.000
Output
$0.000
Where to run it

1 host

Grok 4.1 Fast

No hosts listed on OpenRouter.

Nex-N2.5-Mini (free)1 host
HostInOutContextUptime
NNex AGIbf16degraded$0 in·$0 out·262k·92.2% up

Per million tokens. Prices and uptime via OpenRouter, checked 23 Sep 2026.

Research

What we learned reading every model

FAQ

Common questions

Grok 4.1 Fast is developed by xAI while Nex-N2.5-Mini (free) is developed by Nex AGI. You can compare their actual outputs across 15 challenges on Rival to see how they differ in practice.

It depends on your use case. Grok 4.1 Fast and Nex-N2.5-Mini (free) each have strengths in different areas. Rival lets you compare their real outputs side-by-side across 15 challenges so you can judge which fits your needs best.

This page shows a side-by-side comparison of Grok 4.1 Fast and Nex-N2.5-Mini (free) 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

Grok 4.1 Fast logo
Grok 4.1 Fast59 outputs, specs and price
Nex-N2.5-Mini (free) logo
Nex-N2.5-Mini (free)15 outputs, specs and price
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