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  5. Grok 4 Fast (free)vsMercury 2.5
Updated Sep 2026

Grok 4 Fast (free)vsMercury 2.5

Grok 4 Fast (free) is cheaper than Mercury 2.5 at $0/M vs $0.04/M input tokens.

Grok 4 Fast (free) and Mercury 2.5 compared across 2 shared prompts
SpecGrok 4 Fast (free)Mercury 2.5
Input priceFree$0.04/M tokens
Output priceFree$0.15/M tokens
Context window2.0M tokens260K tokens
Free API (OpenRouter)NoNo
ReleasedSep 2025Sep 2026
Side by side

Same prompt, both answers

Opening lines from every prompt both answered. Formatting stripped, words untouched.

Simple 7-Ingredient Recipe

Create a simple recipe for a delicious dish (sweet or savory) using only 7 common pantry ingredients. Include a creative name for the dish…

Grok 4 Fast (free)240 words
Pantry Hero Pasta Primavera This simple, savory one-pot pasta dish transforms basic staples into a flavorful, garlicky tomato sauce that's comforting and ready in under 30 minutes.
Read the full answer
Mercury 2.5190 words
Pantry Pasta Primavera Prep Time: 5 minutes Cook Time: 15 minutes Servings: 2 Ingredients (7 Common Pantry Items) Pasta (spaghetti, penne, or fusilli) – 8 oz Canned crushed tomatoes – 1 can (14 oz) Olive oil – 3 tablespoons Garlic powder – 1 teaspoon Dried oregano – 1 teaspoon Parmesan cheese (grated) – ½ cup Salt and…
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 Fast (free)849 words
1-Month Plan for Better Health and Longevity This beginner-friendly plan focuses on three foundational areas: diet, exercise, and sleep. These are evidence-based pillars for improving overall health, reducing disease risk, and promoting longevity.
Read the full answer
Mercury 2.5325 words
Here is a simple, actionable 1-month plan to kickstart your journey toward better health and longevity. This guide focuses on three foundational pillars: Nutrition, Movement, and Sleep. Week 1: Awareness & Small Wins Goal: Build habits without overwhelming yourself.
Read the full answer
Our Verdict
Grok 4 Fast (free)
Grok 4 Fast (free)
Mercury 2.5
Mercury 2.5

Not enough votes to call it. On the specs, nothing separates them.

Too close to call
API pricing

Cost per 1M tokens

Grok 4 Fast (free)
Input
$0.000
Output
$0.000
Mercury 2.5
Input
$0.04
Output
$0.15
Where to run it

1 host

Grok 4 Fast (free)

No hosts listed on OpenRouter.

Mercury 2.51 host
HostInOutContextUptime
Inception$0.04 in·$0.15 out·260k·100% up

Per million tokens. Prices and uptime via OpenRouter, checked 22 Sep 2026.

Research

What we learned reading every model

FAQ

Common questions

Grok 4 Fast (free) is developed by xAI while Mercury 2.5 is developed by Inception. Grok 4 Fast (free) has a 2.0M token context window vs Mercury 2.5's 260K. You can compare their actual outputs across 2 challenges on Rival to see how they differ in practice.

It depends on your use case. Grok 4 Fast (free) and Mercury 2.5 each have strengths in different areas. Rival lets you compare their real outputs side-by-side across 2 challenges so you can judge which fits your needs best.

Grok 4 Fast (free) costs $0/M input tokens and Mercury 2.5 costs $0.04/M input tokens. Grok 4 Fast (free) is $0.04/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 Grok 4 Fast (free) and Mercury 2.5 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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