xAI: Grok-4-Fast-Reasoning
Grok-4-Fast-Reasoning is a reasoning model from xAI released on Sep 1, 2025. It reads text and images and writes text, with a 2M token context window and up to 128K tokens per reply.
Show moreShow less
It costs $0.20 per million input tokens and $0.50 per million output tokens. Cached input bills at $0.05, 75% less than fresh input.
It supports tool calling, structured JSON output and prompt caching.
5 providers serve it, including Jiekou.AI, 302.AI and Helicone. The lowest input price is $0.18 per million tokens at Jiekou.AI.
- Modalities
- In / out price
- $0.20 / $0.50 per 1M
- Context
- 2M
- Max output
- 128K
- Released
- Sep 1, 2025
- Knowledge cutoff
- n/a
- Tool calling
- Structured output
- Reasoning
- Prompt caching
- Open weights
- Free to use
Grok-4-Fast-Reasoning pricing
USD, as listed on Oct 15, 2026. Most bills are input heavy, so the cached input rate matters as much as the headline price.
| Input | $0.20 / 1M tokens | |
|---|---|---|
| Output | $0.50 / 1M tokens | |
| Cached input (read) | $0.05 / 1M tokens | 75% off input |
Grok-4-Fast-Reasoning providers
5 providers serve it, including Jiekou.AI, 302.AI and Helicone. The lowest input price is $0.18 per million tokens at Jiekou.AI. Each host sets its own price and limits, so the cheapest one is not always the one with the longest context.
| Provider | Input /M | Output /M | Cache read /M | Context | Max output |
|---|---|---|---|---|---|
| Jiekou.AI | $0.18 | $0.45 | – | 2M | 2M |
| 302.AI | $0.20 | $0.50 | – | 2M | 30K |
| Helicone | $0.20 | $0.50 | $0.05 | 2M | 2M |
| Poe | $0.20 | $0.50 | $0.05 | 2M | 128K |
| Qiniu | n/a | n/a | – | 2M | 2M |
What Grok-4-Fast-Reasoning costs per month
Pick a workload close to yours or type your own volumes.
Supported request parameters
What you can set when you call Grok-4-Fast-Reasoning through an OpenAI compatible API.
- Tools
tools - Structured outputs
structured_outputs - Reasoning
reasoning
Alternatives to Grok-4-Fast-Reasoning
Models that take the same inputs and call tools, closest in price, cheaper ones first.
- Index 39.5
Reads text and images. Tool calling, structured output, reasoning. Served by 55 providers.
by deepseekSep 10, 20261M context$0.15/M input tokens$0.60/M output tokens55 providers
- Index 11.3
Reads text and images. Tool calling, structured output, reasoning. Served by 15 providers.
by mistralaiMar 16, 2026262K context$0.15/M input tokens$0.60/M output tokens15 providers
- Index 41.8
Reads text, images, files and video. Tool calling, structured output, reasoning. Served by 65 providers.
by z-aiAug 21, 20261M context$0.15/M input tokens$0.50/M output tokens65 providers
- Index 39.8
Reads text, images and video. Tool calling, structured output, reasoning. Served by 23 providers.
by qwenAug 26, 20261M context$0.15/M input tokens$0.47/M output tokens23 providers
- Index 14.7
Reads text and images. Tool calling, structured output, reasoning. Served by 38 providers.
by googleApr 2, 2026262K context$0.14/M input tokens$0.40/M output tokens38 providers
- Index 43.4
Reads text, images and files. Tool calling, structured output, reasoning. Served by 26 providers.
by anthropicOct 7, 20261M context$0.10/M input tokens$0.50/M output tokens26 providers
More from xAI
- 1K context
Generates video from text, images and files. Served by 2 providers.
by x-aiOct 1, 20262 providers
- Index 46.5
Reads text, images and files. Tool calling, structured output, reasoning. Served by 22 providers.
by x-aiSep 16, 2026500K context$2/M input tokens$6/M output tokens22 providers
- 500K context
Reads text, images and files. Tool calling, structured output, reasoning. Served by 29 providers.
by x-aiAug 10, 2026$2/M input tokens$6/M output tokens29 providers
- 66K context
Generates images from text and images. Served by 3 providers.
by x-aiAug 7, 2026$0/M input tokens$0/M output tokens3 providers
Grok Voice STT 1.0
Transcription15K contextTurns speech into text.
by x-aiAug 4, 2026
Grok Voice TTS 1.0
Speech15K contextTurns text into spoken audio.
by x-aiJul 31, 2026
Grok-4-Fast-Reasoning questions
How much does the Grok-4-Fast-Reasoning API cost?
$0.20 per million input tokens and $0.50 per million output tokens, with cached input at $0.05. The estimator on this page turns that into a monthly bill for your own workload.
What is the context window of Grok-4-Fast-Reasoning?
2,000,000 tokens of input, and it can write up to 128,000 tokens in one reply. As a rough guide, a million tokens is around 750,000 English words.
Which providers serve Grok-4-Fast-Reasoning?
5 providers serve it, including Jiekou.AI, 302.AI and Helicone. The lowest input price is $0.18 per million tokens at Jiekou.AI. Prices differ by host, so the Providers table on this page lists each one with its input and output price.
Does Grok-4-Fast-Reasoning support tool calling?
Yes. It accepts tool definitions and can return JSON that matches a schema, which is what an agent needs to call your APIs.
Is Grok-4-Fast-Reasoning open source?
No. xAI serves it through an API only, so you cannot download the weights or host it yourself.
When was Grok-4-Fast-Reasoning released?
Sep 1, 2025.
Catalog data from models.dev (MIT licensed), refreshed daily, last on Oct 15, 2026. The summary is written from these facts.
Building on Grok-4-Fast-Reasoning?
I test your real tasks on it and the two closest alternatives, then ship the agent on whichever wins on cost and accuracy.
Book Meeting