Model detail
grok-4-fast-reasoning
Grok 4 Fast is xAI's latest multimodal model with SOTA cost-efficiency and a 2M token context window. It comes in two flavors: non-reasoning and reasoning. Read more about the model on xAI's [news post](http://x.ai/news/grok-4-fast). Reasoning can be enabled/disabled using the `reasoning` `enabled` parameter in the API. [Learn more in our docs](https://openrouter.ai/docs/use-cases/reasoning-tokens#controlling-reasoning-tokens)
Model specs
- Context length
- –
- Max output
- –
- I/O modalities
- –
- Released
- 2025-09
02
API endpoints
One MixRoute gateway, OpenAI-compatible
-
OpenAI-compatible
/v1/chat/completionsPOST -
OpenAI-compatible
/v1/responsesPOST
03
Pricing
Flat rate, unit: /1M Tokens
Input
$0.2000 /1M Tokens
Completion
$0.5000 /1M Tokens
Cache read
$0.0500 /1M Tokens
08
Token cost estimator
Live estimate from this page's pricing, not an actual bill
Share of the same prefix read repeatedly, up to 100%
One endpoint, a testable decision
Test this model and alternate routes with the same request format
Start from a real workload, then let quality, total cost, and failure conditions decide whether to send production traffic.