Grok 4 Fast Reasoning

As we continue advancing Grok, we are retiring several earlier models to focus fully on our newest generation. **Effective May 15, 2026 at 12:00pm PT**, the following models will be retired from the xAI API:

* `grok-4-1-fast-reasoning`
* `grok-4-1-fast-non-reasoning`
* `grok-4-fast-reasoning`
* `grok-4-fast-non-reasoning`
* `grok-4-0709`
* `grok-code-fast-1`
* `grok-3`
* `grok-imagine-image-pro`

[`https://docs.x.ai/developers/migration/may-15-retirement`](https://docs.x.ai/developers/migration/may-15-retirement)

Have you ever tried any of them? What was your experience using them?

We just did the biggest multi-provider update since launch, so here’s a quick brain dump of what changed and why it matters if you care about *which* model you’re actually talking to.

We’ve added:

* Google Gemini 2.5 Flash and 2.5 Pro
* Anthropic Claude 4.5 Sonnet and Claude 4.5 Haiku
* xAI Grok-3, Grok-3-mini, Grok-4-fast-reasoning, Grok-4-fast-non-reasoning, and Grok-code-fast-1

And the important part: all of these sit *side-by-side* with multiple GPT-4o checkpoints (May ’24, August ’24, Nov ’24, latest), plus GPT-5 / 5.1 and Echo, in one router-free workspace.

No mystery “best of” switch, no invisible downgrades. You pick the exact model, and that’s what you get.

[The new model selector on just4o.chat](https://preview.redd.it/p6w7231tfz1g1.jpg?width=3417&format=pjpg&auto=webp&s=3d0ca882c82e68feb608a309185d4069fc289971)

# What this unlocks in practice

You can now do stuff like:

* Keep Claude 4.5 Sonnet wired in as a long-running coding/agent persona for a project, while
* Using a specific GPT-4o checkpoint for writing and formatting because you like that era’s “feel,” and
* Hand the gnarly reasoning questions to GPT-5 or Gemini 2.5 Pro, and
* Let Grok-code-fast-1 or Grok-3 be your “spicy second opinion” on code and math.

All in the same project, with shared memory, without having to guess what the backend routed you to this time.

If you’ve ever thought “I liked 4o in mid-2024 better than whatever this is now,” this is basically the platform built around that feeling.

# Why new additions matter

* **Gemini 2.5 Flash / Pro** Flash is the fast, cheap multimodal workhorse; Pro is the deeper reasoning model that’s genuinely solid for code and long context. Having both means you can treat Gemini like a real stack: Flash for “do it now,” Pro for “think about this properly” — and compare them directly against 4o checkpoints and GPT-5.
* **Claude 4.5 Sonnet / Haiku** Sonnet is the “serious work” Claude: coding, agents, long-running tasks, careful analysis. Haiku is the fast, cost-efficient Claude you can keep on all day for chat, support, and internal tools. Together they give you Anthropic’s vibe at both the “heavy” and “everyday” layers.
* **Grok-3, Grok-3-mini, Grok-4-fast-\*, Grok-code-fast-1** Grok-3 is the big reasoning model, Grok-3-mini is the small logic brain with visible thinking traces, Grok-4-fast comes in reasoning + non-reasoning flavours (deep vs “just answer”), and Grok-code-fast-1 is tuned for code. Basically: the full Grok toolbox, not just a single “Grok” toggle.

And all of them are first-class citizens in the UI, not bolted-on curiosities.

# Near future: Gemini 3.0 + Grok 4.1

The other piece of the story is what’s coming next:

* **Gemini 3.0** is rolling out on Google’s side and is being pitched as their smartest generation yet. Once the APIs stabilise and pricing/docs are sane, we’ll wire Gemini 3.0 into [just4o.chat](http://just4o.chat) the same way: explicit model entries, no surprise swaps, living next to your favourite 4o checkpoints.
* **Grok 4.1** is already starting to show up across xAI’s own products as the next-gen Grok, with better conversational intelligence and “feels more like a person” vibes. As soon as 4.1 is properly exposed on the API, it’ll join the Grok lineup in our picker as its own selectable model, not a stealth replacement.

So if you want a place where you can actually *feel* the difference between eras (old 4o vs new 4o, Gemini 2.5 vs 3.0, Grok-3 vs 4.1, etc.), that’s what we’re building towards.

# TL;DR

If you care which checkpoint you’re on, if you miss how 4o felt in 2024, if you want Claude + Gemini + Grok + GPT-5 all in the same room, and you want **no routing, no downgrades, no hidden switches**, then the new model lineup on [just4o.chat](http://just4o.chat) is for you.

Would love feedback on:

* Which provider you’re most excited about (Gemini / Claude / Grok)
* Which *specific* GPT-4o checkpoint you still miss in ChatGPT
* What models and features (web search? image gen?) you want to see next

Drop ideas below and we’ll build 'em.

# TL;DR

**Grok 4 Fast just launched today (Sept 22, 2025) from xAI – the ultra-fast, cost-crushing AI beast with a massive 2M token context window!** It's 40% more token-efficient than rivals, multimodal for text+images, and splits into "reasoning" (deep thinks) vs "non-reasoning" (blazing speed) modes. Beats GPT-4o on speed/cost, matches Gemini's context but crushes pricing. Perfect for devs, researchers, and creators – here's how to unleash it like a pro. (Free tier on OpenRouter; premium via xAI API.)

**The Dawn of Affordable AI Superpowers: Why Grok 4 Fast is About to Flip the Script on Big Tech (And How You Can Ride the Wave)**

**xAI is shipping and is catching up to top models like ChatGPT and Gemini.**

Imagine an AI that doesn't just *think* like a genius, but does it at warp speed, for pennies, while juggling entire novels' worth of context in one go. No more "sorry, I forgot the plot from page 47" moments. Today, xAI (Elon Musk's truth-seeking squad) dropped **Grok 4 Fast** – and it's not just another model; it's a revolution in making elite AI accessible to *everyone*, not just Fortune 500 wallets. This isn't hype; it's the tool that'll empower indie devs, solo researchers, and dream-chasing creators to outpace the giants. Buckle up – we're diving deep into what makes it tick, how it stacks up, killer use cases, and pro hacks to make it your secret weapon. Let's build the future, one prompt at a time.

# What's Revolutionary About Grok 4 Fast?

At its core, Grok 4 Fast is xAI's bold bet on blending raw power with insane efficiency so AI isn't a luxury, but a launchpad for human potential. Here's the innovation breakdown:

* **Unified Architecture Magic**: Unlike clunky rivals that force you into "slow mode" for smarts, Grok 4 Fast rolls out as *two seamless flavors* – **grok-4-fast-reasoning** for chain-of-thought puzzles and **grok-4-fast-non-reasoning** for lightning-quick tasks. Switch on the fly without retraining your brain (or wallet). This unified setup integrates reasoning *and* speed, trained via reinforcement learning to handle multimodal inputs (text + images) like a pro.
* **The 2M Token Context Window Beast**: Picture this – most AIs choke on 128K tokens (that's \~100 pages). Grok 4 Fast swallows **2 million tokens** (\~1,500 pages or a full codebase + docs). Feed it your entire project history, legal docs, or a novel draft, and it *remembers* without hallucinating gaps. This isn't incremental; it's a game-changer for long-form analysis, where context is king.
* **Cost-Efficiency on Steroids**: It slashes token usage by **40%** compared to peers, with low cache read costs that make iterative workflows dirt cheap. Trained to be "fast, cheap, powerful," it's flipping the economics for startups – think Replit or Lovable building AI-native apps without breaking the bank.

This isn't just tech; it's inspirational fuel. In a world where AI feels like an elite club, Grok 4 Fast whispers, "You belong here. Build boldly." As xAI puts it, it's setting a "new standard for cost-efficient intelligence." Educational nugget: Its multimodal smarts (processing images alongside text) open doors to visual reasoning, like analyzing charts in real-time during a brainstorm.

# Head-to-Head: Grok 4 Fast vs. The Big Dogs (Gemini 2.5 Pro/Fast, Claude 4 Sonnet/4.1 Opus)

We've all chased the "best AI" dragon, but benchmarks don't lie (much). Grok 4 Fast isn't claiming the crown on every metric – yet – but it *owns* the value equation, hitting Gemini 2.5 Pro-level intelligence at \~25x better cost-efficiency on the frontier. Quick comparison table for the win (based on Artificial Analysis Intelligence Index v3.0, incorporating 10 evals like MMLU-Pro, GPQA Diamond, and LiveCodeBench):

|Feature/Metric|Grok 4 Fast|Gemini 2.5 Pro (Google)|Gemini 2.5 Fast (Google)|Claude 4 Sonnet (Anthropic)|Claude 4.1 Opus (Anthropic)|
|:-|:-|:-|:-|:-|:-|
|**Intelligence Index (v3.0)**|60|60|55|57|62|
|**Context Window**|2M tokens|1M tokens (2M soon)|1M tokens|1M tokens|200K tokens|
|**Speed (Tokens/Sec)**|Ultra-fast (SOTA for cost/speed)|Faster than avg.|Fastest/low latency|Slower than avg.|Moderate, coding-optimized|
|**Price (Input/Output per 1M Tokens)**|\~$0.10/$0.30 (25x cost frontier edge)|$1.25/$10|$0.30/$2.50|$3/$15|$15/$75|
|**Multimodal?**|Yes (text+images)|Yes (text/image/video/audio)|Yes (text/image/video)|Yes (text+images)|Yes (text+images)|
|**Strengths**|Cost-efficiency, dual modes, low cache, balanced reasoning|Enhanced reasoning, vast datasets, strong multimodal|Price/performance balance, low latency for tasks|Coding (SWE-bench 72.7%), ethical reasoning|Advanced coding/agents (SWE-bench 74.5%), precision|
|**Weaknesses**|New kid (fewer integrations)|Higher cost for volume|Less depth on complex reasoning|Slower speed|Very expensive, smaller context|

*Sources: Aggregated from Artificial Analysis benchmarks & provider docs.* Bottom line? Grok 4 Fast ties Gemini 2.5 Pro on raw smarts (both at 60 on the Index) but dominates on cost and context – ideal if you're scaling workflows without VC cash. For speed demons, Gemini 2.5 Fast edges out; Claude 4 Sonnet shines in code ethics; Opus 4.1 for pro-level agents but at a premium. If you're grinding daily (devs, analysts), Grok's your dark horse – punching above its weight like a budget superhero.

# How Grok 4 Fast Compares to the Competition

The AI market is a battlefield, with giants like Google's Gemini, Anthropic's Claude, and OpenAI's GPT models all vying for the top spot. Here's where Grok 4 Fast punches above its weight:

* **vs. Gemini 2.5 Pro:** Grok 4 Fast is now a direct competitor to Gemini 2.5 Pro, particularly with its large context window. While Gemini has its own impressive multimodal capabilities, early LMArena benchmarks show Grok 4 Fast ranking first in search-related tasks, an area where its real-time data integration with X gives it a significant edge.
* **vs. GPT-4o / GPT-5:** Grok 4 Fast’s major advantage is its speed and cost. While models like GPT-5 are known for their peak performance on complex tasks, Grok 4 Fast is positioned as the "daily driver." It's optimized for rapid iteration and high-volume workloads, making it far more practical for everyday coding, drafting, and research. Its cost-to-performance ratio is particularly attractive for developers.
* **vs. Claude 4.1:** Claude is known for its reliability and excellent instruction-following, especially for long-form creative writing and enterprise applications. Grok 4 Fast, while also capable, is designed for a different workflow: one that prioritizes quick, actionable results. If you need rapid-fire code suggestions or quick summaries of documents, Grok 4 Fast is often the faster and more affordable choice.

# Market Disruption: The Economics of Accessible Intelligence

The pricing structure of Grok 4 Fast represents a paradigmatic shift in AI economics, with input tokens priced at $0.20 per million and output tokens at $0.50 per million for contexts under 128,000 tokens. This pricing model delivers approximately 25 times better cost efficiency compared to competing frontier models like Gemini 2.5 Pro, which charges $1.25 input and $10 output per million tokens. Even when compared to GPT-5's pricing of $1.25 input and $10 output, Grok 4 Fast maintains a significant cost advantage while delivering competitive intelligence levels.

This cost disruption has immediate implications for enterprise deployment strategies. Companies processing millions of tokens daily can expect substantial savings—a workload costing $540 monthly with Claude 4 Sonnet could run for approximately $210 with Grok 4 Fast, representing over 60% cost reduction while maintaining comparable performance. The model's cached input pricing at $0.05 per million tokens makes iterative workflows particularly cost-effective, enabling sustained conversations and complex multi-turn interactions without prohibitive expenses.

# Best Use Cases: Where Grok 4 Fast Shines Brightest

This model's built for *action*, not chit-chat. Here are tailored scenarios to spark your genius:

1. **Developer Workflows**: Debug entire repos in one prompt – paste 500K+ lines of code + specs, get optimized fixes. (Pro: Low cache costs mean endless iterations.)
2. **Research & Analysis**: Summarize 1,000-page reports or academic papers. Multimodal bonus: Upload charts/images for instant insights, like "Explain this quantum sim + predict outcomes."
3. **Content Creation**: Draft novels, scripts, or marketing campaigns with full arc memory. Non-reasoning mode for quick outlines; reasoning for plot twists.
4. **Finance & Science**: Model complex sims (e.g., climate data over decades) or forecast markets with historical context. Handles math/science prompts like a PhD on caffeine.
5. **Business Tools**: Power no-code / low code apps (e.g., Cursor) or customer support with personalized, context-aware responses – all at startup-friendly prices.

# Best Practices & Pro Tips: Level Up Your Grok Game

Don't just prompt – *engineer* them. Here's your cheat sheet for viral results:

* **Best Practice #1: Chunk Smartly**: With 2M tokens, resist the urge to dump everything. Structure as "Section 1: Background \[paste\]. Section 2: Query \[ask\]." Keeps it focused, reduces hallucinations.
* **Pro Tip #1: Mode-Switch Like a Boss**: Use non-reasoning for drafts ("Quick brainstorm 5 ideas"), flip to reasoning for depth ("Chain-think: Why does this fail? Alternatives?"). Saves 30-50% on costs.
* **Best Practice #2: Multimodal Mastery**: Always tag images ("Analyze this graph: \[upload URL\]"). For videos? Chain with text summaries first.
* **Pro Tip #2: Iterate with Constraints**: Start prompts with "Respond in 200 words max, numbered list, cite sources." Forces tight, actionable output – and leverages its efficiency.
* **Best Practice #3: API Integration**: Hook it to tools via function calling (e.g., Zapier for automations). Free tier on OpenRouter for testing; scale to xAI API for prod.
* **Pro Tip #3: Cache Hacks**: Reuse sessions for ongoing chats – its low read costs make threaded convos (e.g., evolving a business plan) feel free.

# 5 Ideal Prompts to Test Grok 4 Fast's True Power

These prompts are designed to showcase Grok 4 Fast's standout features: its massive 2M token context window for handling huge inputs, multimodal capabilities (text + images), dual modes (reasoning for depth, non-reasoning for speed), and efficiency in complex tasks like coding, analysis, and creation. Copy-paste them directly into Grok (via xAI API, OpenRouter, or the app) – start with non-reasoning mode for quick tests, switch to reasoning for deeper dives. Watch it crush long-context recall, multimodal reasoning, and cost-effective iteration!

1. **Long-Context Codebase Analysis (Tests 2M Token Window & Dev Efficiency)** *Prompt:* "Here's my entire 500K+ token Python codebase for a full-stack e-commerce app \[paste your repo/code here or simulate with a long snippet\]. First, summarize the architecture in a numbered diagram. Then, in reasoning mode, identify 3 security vulnerabilities, suggest fixes with code snippets, and simulate running the updated auth module. Output in Markdown for easy reading." *Why it shines:* Grok 4 Fast ingests massive codebases without losing details, debugging like a senior engineer – perfect for devs iterating on projects without context resets.
2. **Multimodal Research Synthesis (Tests Image/Text Integration & Analysis Depth)** *Prompt:* "Analyze this uploaded chart of global climate data from 1900-2025 \[upload image URL or describe\]. Cross-reference it with this 1M-token excerpt from IPCC reports \[paste long text\]. In non-reasoning mode, generate a 5-bullet executive summary. Switch to reasoning: Predict 2050 trends using chain-of-thought, citing specific data points, and propose 3 policy interventions with pros/cons tables." *Why it shines:* Combines visual + textual smarts for instant insights, outperforming rivals on long docs – ideal for researchers turning raw data into actionable foresight.
3. **Creative Content Generation with Full Arc Memory (Tests Storytelling & Speed)** *Prompt:* "Build a 10-chapter sci-fi novel outline based on this 800K-token world-building bible \[paste detailed lore/docs\]. Include character arcs, plot twists, and themes of AI ethics. In non-reasoning mode, draft Chapter 1 (500 words). Then reasoning mode: Revise for pacing issues, ensuring consistency across the full outline, and end with a teaser for a sequel." *Why it shines:* Handles epic-scale creativity without forgetting threads, generating polished drafts fast – a game-changer for writers scaling from idea to manuscript.
4. **Financial Modeling & Forecasting (Tests Math/Science Precision & Efficiency)** *Prompt:* "Using this 1.5M-token historical dataset of S&P 500 trades, earnings reports, and economic indicators from 2000-2025 \[paste CSV/text data\], build a Monte Carlo simulation in Python code. In reasoning mode, forecast Q4 2025 volatility under 3 scenarios (recession, boom, neutral), output results in a plot description and risk assessment table. Optimize for low token use." *Why it shines:* Crunches huge datasets with accurate math, outputting code + visuals efficiently – empowers analysts to model futures without enterprise costs.
5. **Ethical Agent Simulation (Tests Reasoning Modes & Business Tools)** *Prompt:* "Simulate a customer support agent for a fintech app. Context: Full 2M-token user handbook, privacy policy, and 100K-token chat logs \[paste docs\]. Scenario: User query – 'My account was hacked, refund $10K now!' In non-reasoning mode, draft a empathetic 3-response thread. Switch to reasoning: Evaluate ethical/legal risks, escalate if needed, and generate a follow-up audit report with anonymized insights." *Why it shines:* Balances speed for real-time chats with deep ethical reasoning, scaling personalized support – revolutionary for startups building AI agents on a budget.

Get great prompts like the ones in this post for free at [PromptMagic.dev](http://promptmagic.dev./)