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Grok 4 Fast (reasoning) vs Kimi K3

Compare Grok 4 Fast (reasoning) from Grok and Kimi K3 from Moonshot AI 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)Moonshot AIKimi K3
+ 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
Moonshot AI logo
Kimi K3
Moonshot AI · text, image, video → text

Kimi K3 is Kimi’s flagship model for long-horizon coding and end-to-end knowledge work, with a 1M-token context window and industry-leading intelligence.

Input$3.00 /M
Output$15.00 /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)
Kimi K3
Input /M
$0.20
$3.00
Output /M
$0.50
$15.00
Cache read /M
$0.05
$0.30
Context length
2,000,000
1,048,576
Max output
30,000
1,048,576
Time to First Token
2.7 s
0.9 s
Throughput
136.9 tok/s
73.1 tok/s
Modalities
textimage
textimagevideo
Supported Parameters
thinkingtoolsfunction callingstructured outputs
thinkingfunction callingstructured outputs
API Formats
Released
-
-

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-reasoningkimi-k3

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-reasoningkimi-k3

Throughput (tok/s)

-

TTFT (s)

-

Uptime (%)

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LMArena Benchmarks

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

Text
grok-4-fast-reasoningkimi-k3
1360142014801540
Overall
14041486
Coding
14371531
Math
14121412
Hard prompts
14131505
Instruction following
13881479
Multi-turn
14061499
Creative writing
13811470
Longer query
14121502
Chinese
14431527
English
14141491

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
Kimi K3
$405 /mo

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

FAQ

Which is cheaper: Grok 4 Fast (reasoning), Kimi K3?

Grok 4 Fast (reasoning): $0.50/M output tokens; Kimi K3: $15.00/M. Use the cost calculator above to estimate your own workload.

How do their coding arena scores compare?

Kimi K3: 1531; Grok 4 Fast (reasoning): 1437 (LMArena coding leaderboard).

Which responds faster?

Kimi K3: 0.9s 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 Kimi K3 accepts 1,048,576 input tokens. Maximum output per request is 30,000 tokens on Grok 4 Fast (reasoning) and 1,048,576 tokens on Kimi K3.

Which one generates tokens faster?

Grok 4 Fast (reasoning) at 136.9 tok/s and Kimi K3 at 73.1 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; Kimi K3 accepts text, image and video input and supports thinking, function calling and structured outputs.

Can I call Grok 4 Fast (reasoning) and Kimi K3 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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