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SpaceXAI

Grok 4 Fast

grok-4-fast-reasoning

48Index
ClosedGenerally available2M contextTextImage

Pick this when

Two-million-token prompts: dumps, logs, multi-doc review, cheap long context.

Skip when

You need frontier reasoning. Fast is a window, not a brain.

The context number is real. Effective use of the far end of a 2M window still varies. Test on your own documents.

Price

Input / 1M
$0.20
Output / 1M
$0.50
Measured task
$0.18

Largest practical context window in this catalog.

Shape

Context
2M
Max output
32K
Released
2026-06
Tools
Yes
Reasoning
Yes

Scores

Intelligence index48
GPQA Diamond72
Terminal-Bench 2.155
Agentic index25
Arena
—
Speed
210/s
GPQA
72.1%
Term.
54.8%
  • AA Index. The single number most people mean by “how smart.” It is a blend, so a specialist can lose here and still win the job you care about.
  • GPQA. A clean test of hard reasoning. PhD experts sit around 65%. It says little about writing, tools, or taste.
  • Term.. Closest public proxy for coding agents that live in a terminal. A high index score with a weak terminal score is a warning.
  • Arena. Captures taste and usefulness that unit tests miss. Sample size varies by model, so treat gaps under ~100 Elo as noise.

SpaceXAI · Palo Alto / Memphis. Grok. Wired into X and the live web. Grok 4.6 sits on the frontier scoreboard at a mid-tier price. Context is 500K, half of the pack.

Compiled 2026-08-28 from public Artificial Analysis, LMSYS-style arena, and first-party price sheets. Scores move. Recheck before you spend.

A two-point gap on the intelligence index is noise for most work. Cost per finished task is the number that shows up on the invoice.