GPT-5.5 Instant vs Grok 4 Fast
GPT-5.5 Instant and Grok 4 Fast are closely matched at 32.3 and 31.7 on the LLM Stats Score. Grok 4 Fast is 40.9x cheaper per token.
OpenAI · xAI · Updated for 2026
Which is better?
GPT-5.5 Instant and Grok 4 Fast are closely matched on the overall LLM Stats Score at 32.3 and 31.7.
In the 2 individual benchmarks reported for both models, Grok 4 Fast wins 2; this is a narrower head-to-head signal than the composite indexes.
On price, Grok 4 Fast is roughly 40.9x 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 GPT-5.5 Instant
- you want the most recent training data — it shipped May 2026
Choose Grok 4 Fast
- you value its reported benchmark strengths — it wins 2 of 2 exact shared results
- cost matters — it's about 40.9x cheaper per token
- you process long inputs — it offers a 2,000,000 token context window
At a glance
The differences that matter most.
Individual benchmarks
9 reported for GPT-5.5 Instant · 7 for Grok 4 Fast
GPT-5.5 Instant outperforms in 0 benchmarks, while Grok 4 Fast is better at 2 benchmarks (AIME 2025, GPQA).
Grok 4 Fast 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, GPT-5.5 Instant ($5.00/1M tokens) is 25.0x more expensive than Grok 4 Fast ($0.20/1M tokens).
For output processing, GPT-5.5 Instant ($30.00/1M tokens) is 60.0x more expensive than Grok 4 Fast ($0.50/1M tokens).
In conclusion, GPT-5.5 Instant is more expensive than Grok 4 Fast.*
* 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 GPT-5.5 Instant's 400,000 tokens. GPT-5.5 Instant can generate longer responses up to 128,000 tokens, while Grok 4 Fast is limited to 30,000 tokens.
Input capabilities
Documented input modalities across available providers
Both GPT-5.5 Instant and Grok 4 Fast support multimodal inputs.
They are both capable of processing various types of data, offering versatility in application.
GPT-5.5 Instant
Grok 4 Fast
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
GPT-5.5 Instant was released on 2026-05-05, while Grok 4 Fast was released on 2025-08-28.
GPT-5.5 Instant is 8 months newer than Grok 4 Fast.
May 5, 2026
4 months ago
8mo newerAug 28, 2025
1.1 years ago
Knowledge Cutoff
When training data ends
GPT-5.5 Instant has a documented knowledge cutoff of 2025-08-31, while Grok 4 Fast's cutoff date is not specified.
We can confirm GPT-5.5 Instant's training data extends to 2025-08-31, but cannot make a direct comparison without Grok 4 Fast's cutoff date.
Aug 2025
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Provider Availability
GPT-5.5 Instant is available from OpenAI. Grok 4 Fast is available from xAI.
GPT-5.5 Instant
Grok 4 Fast
Outputs Comparison
Judge for yourself.
Run your own prompts against GPT-5.5 Instant and Grok 4 Fast side-by-side, then vote on the output you prefer.
FAQ
Common questions about GPT-5.5 Instant vs Grok 4 Fast.