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Grok 4 Fast (reasoning) vs Grok 4.5

Compare Grok 4 Fast (reasoning) from Grok and Grok 4.5 from Grok on key metrics including benchmarks, price, context length, and other model features. Access both models and hundreds of others through the AIHubMix API.

GrokGrok 4 Fast (reasoning)GrokGrok 4.5
+ Add model · 2/4
Grok logo
Grok 4 Fast (reasoning)
Grok · text, image → text

Grok-4-fast is a cost-effective inference model developed by xAI that delivers cutting-edge performance with excellent token efficiency. The model features a 2 million token context window, advanced Web and X search capabilities, and a unified architecture supporting both "inference" and "non-inference" modes. Compared to Grok 4, it reduces thinking tokens by an average of 40% and lowers the price by 98% while achieving the same performance.

Input$0.20 /M
Output$0.50 /M
Details
Grok logo
Grok 4.5
Grok · text, image → text

Grok 4.5 was trained on datasets spanning knowledge in coding, science, engineering, and math. With both intelligent and efficient reasoning, Grok 4.5 excels at real engineering tasks and exceeds comparable leading models at these tasks.

Input$2.00 /M
Output$6.00 /M
Details

Pricing & Specifications

Prices are per million tokens. Time to First Token and throughput are rolling averages measured on AIHubMix.

Grok 4 Fast (reasoning)
Grok 4.5
Input /M
$0.20
$2.00
Output /M
$0.50
$6.00
Cache read /M
$0.05
$0.50
Context length
2,000,000
500,000
Max output
30,000
500,000
Time to First Token
2.7 s
1.5 s
Throughput
136.9 tok/s
25.4 tok/s
Modalities
textimage
textimage
Supported Parameters
thinkingtoolsfunction callingstructured outputs
thinkingtoolsfunction callingstructured outputslong context
API Formats
Released
-
July 2026

Promotional prices show the discounted rate; see each model page for promotion windows.

Activity Past 30 Days

Daily traffic served through AIHubMix — how demand for each model is trending.

grok-4-fast-reasoninggrok-4.5

Tokens / day

-

Requests / day

-

Performance Past 3 Days

Measured on real AIHubMix traffic, hourly buckets. Gaps mean no traffic in that hour.

grok-4-fast-reasoninggrok-4.5

Throughput (tok/s)

-

TTFT (s)

-

Uptime (%)

-

LMArena Benchmarks

LMArena ratings by capability (Bradley-Terry, commonly called Elo). Higher is better.

Text
grok-4-fast-reasoninggrok-4.5
1360142014801540
Overall
14041470
Coding
14371523
Math
14121478
Hard prompts
14131495
Instruction following
13881466
Multi-turn
14061477
Creative writing
13811449
Longer query
14121485
Chinese
14431511
English
14141475
WebDev Arena
grok-4-fast-reasoninggrok-4.5
1120126014001540
Overall
11501556
React
15591559
HTML
11571577
Gaming
15861586
Simulations
15981598
Data analytics
15221522

Source: LMArena (arena.ai) leaderboard, imported by AIHubMix. Models without published ratings are omitted per chart.

Cost calculator

Estimate your monthly bill for the same workload on each model.

Grok 4 Fast (reasoning)
$19.50 /mo
Grok 4.5
$210 /mo

Monthly = daily × 30. Discounted rates applied where a promotion is active.

FAQ

Which is cheaper: Grok 4 Fast (reasoning), Grok 4.5?

Grok 4 Fast (reasoning): $0.50/M output tokens; Grok 4.5: $6.00/M. Use the cost calculator above to estimate your own workload.

How do their coding arena scores compare?

Grok 4.5: 1523; Grok 4 Fast (reasoning): 1437 (LMArena coding leaderboard).

Which responds faster?

Grok 4.5: 1.5s time to first token measured on AIHubMix; see the live performance charts above for how each model behaves across the day.

How large is each context window?

Grok 4 Fast (reasoning) accepts 2,000,000 and Grok 4.5 accepts 500,000 input tokens. Maximum output per request is 30,000 tokens on Grok 4 Fast (reasoning) and 500,000 tokens on Grok 4.5.

Which one generates tokens faster?

Grok 4 Fast (reasoning) at 136.9 tok/s and Grok 4.5 at 25.4 tok/s, measured as output throughput on AIHubMix — a separate metric from time to first token.

What inputs and capabilities does each model support?

Grok 4 Fast (reasoning) accepts text and image input and supports thinking, tool calling, function calling and structured outputs; Grok 4.5 accepts text and image input and supports thinking, tool calling, function calling, structured outputs and long context.

Can I call Grok 4 Fast (reasoning) and Grok 4.5 with the same API key?

Yes. AIHubMix serves every model on this page behind one OpenAI-compatible endpoint, so switching between them is a one-line change to the model field — no second account, key or SDK.

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