Grok 4 Fast vs Mercury 3
Grok 4 Fast and Mercury 3 are closely matched at 31.2 and 36.1 on the LLM Stats Score. Mercury 3 is 1.7x cheaper per token.
xAI · Inception · Updated for 2026
Which is better?
Grok 4 Fast and Mercury 3 are closely matched on the overall LLM Stats Score at 31.2 and 36.1.
In the 1 individual benchmarks reported for both models, Mercury 3 wins 1; this is a narrower head-to-head signal than the composite indexes.
On price, Mercury 3 is roughly 1.7x cheaper per token on a blended 3:1 input/output basis, which adds up quickly at production volume.
Grok 4 Fast also accepts a larger context window (2,000,000 input tokens), making it the stronger choice for long documents and large codebases.
Based on current LLM Stats indexes, shared benchmarks, pricing, and model metadata for 2026.
Choose Grok 4 Fast
- you process long inputs — it offers a 2,000,000 token context window
Choose Mercury 3
- you value its reported benchmark strengths — it wins 1 of 1 exact shared results
- cost matters — it's about 1.7x cheaper per token
- you want the most recent training data — it shipped Oct 2026
At a glance
The differences that matter most.
Individual benchmarks
7 reported for Grok 4 Fast · 12 for Mercury 3
Grok 4 Fast outperforms in 0 benchmarks, while Mercury 3 is better at 1 benchmark (GPQA).
Mercury 3 significantly outperforms across most benchmarks.
Human preference
Blind head-to-head votes and playground preference scores
Pricing Analysis
Price comparison per million tokens
For input processing, Grok 4 Fast ($0.20/1M tokens) is 2.0x more expensive than Mercury 3 ($0.10/1M tokens).
For output processing, Grok 4 Fast ($0.50/1M tokens) is 1.4x more expensive than Mercury 3 ($0.35/1M tokens).
In conclusion, Grok 4 Fast is more expensive than Mercury 3.*
* Using a 3:1 ratio of input to output tokens
Context Window
Maximum input and output token capacity
Grok 4 Fast accepts 2,000,000 input tokens compared to Mercury 3's 1,000,000 tokens. Mercury 3 can generate longer responses up to 131,072 tokens, while Grok 4 Fast is limited to 30,000 tokens.
Input capabilities
Documented input modalities across available providers
Grok 4 Fast supports multimodal inputs, whereas Mercury 3 does not.
Grok 4 Fast can handle both text and other forms of data like images, making it suitable for multimodal applications.
Grok 4 Fast
Mercury 3
License
Usage and distribution terms
Both models are licensed under proprietary licenses.
Both models have usage restrictions defined by their respective organizations.
Proprietary
Closed source
Proprietary
Closed source
Release Timeline
When each model was launched
Grok 4 Fast was released on 2025-08-28, while Mercury 3 was released on 2026-10-19.
Mercury 3 is 14 months newer than Grok 4 Fast.
Aug 28, 2025
1.1 years ago
Oct 19, 2026
0 days ago
1.1yr newerKnowledge Cutoff
When training data ends
Neither model specifies a knowledge cutoff date.
Unable to compare the recency of their training data.
Provider Availability
Grok 4 Fast is available from xAI. Mercury 3 is available from Inception.
Grok 4 Fast
Mercury 3
Outputs Comparison
Judge for yourself.
Run your own prompts against Grok 4 Fast and Mercury 3 side-by-side, then vote on the output you prefer.
FAQ
Common questions about Grok 4 Fast vs Mercury 3.