# xAI Grok 4.1 Fast Reasoning — deprecation status

> Yes — Grok 4.1 Fast Reasoning is retired. xAI shut it down on May 15, 2026; API requests to it now fail. The recommended replacement is Grok 4.3.

A 2M-context reasoning model that was, for a few months, the cheapest way to put a long document in front of a frontier model. It retired on 15 May 2026, and the slug still resolves - requests are silently served by grok-4.3 at grok-4.3 prices, which is the trap in this whole retirement wave.

## Facts

| Field | Value |
| --- | --- |
| Provider | xAI |
| Model id | `grok-4-1-fast-reasoning` |
| Status | Retired |
| Shutdown | May 15, 2026 (80 days ago) |
| Last verified | August 3, 2026 |

## Replacement

- **Grok 4.3** (`grok-4.3`) · recommended — https://modeldeprecations.dev/xai/grok-4.3
  - xAI maps this id to grok-4.3 with reasoning effort "low". The slug keeps working, so nothing breaks - but you are billed $1.25/$2.50 per million instead of the old rate, and the context window drops from 2M to 1M.
  - Parameters it accepts: https://modelparams.dev/models/xai/grok-4.3

```diff
- "model": "grok-4-1-fast-reasoning"
+ "model": "grok-4.3"
```

## FAQ

### When did xAI Grok 4.1 Fast Reasoning shut down?

xAI Grok 4.1 Fast Reasoning shut down on May 15, 2026. API requests to it fail from that date onward.

### What replaces xAI Grok 4.1 Fast Reasoning?

xAI recommends Grok 4.3 (`grok-4.3`) as the replacement for xAI Grok 4.1 Fast Reasoning. xAI maps this id to grok-4.3 with reasoning effort "low". The slug keeps working, so nothing breaks - but you are billed $1.25/$2.50 per million instead of the old rate, and the context window drops from 2M to 1M.

### Is xAI Grok 4.1 Fast Reasoning still available?

No. xAI Grok 4.1 Fast Reasoning is retired and no longer served — it was shut down on May 15, 2026. Calls to it return an error.

### How do I migrate from xAI Grok 4.1 Fast Reasoning to grok-4.3?

Swap the model id in your API call: replace "grok-4-1-fast-reasoning" with "grok-4.3". xAI maps this id to grok-4.3 with reasoning effort "low". The slug keeps working, so nothing breaks - but you are billed $1.25/$2.50 per million instead of the old rate, and the context window drops from 2M to 1M.

## Sources

- [Grok Model Retirement on May 15, 2026](https://docs.x.ai/developers/migration/may-15-retirement) — accessed 2026-08-03

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Canonical page: https://modeldeprecations.dev/xai/grok-4-1-fast-reasoning
JSON: https://modeldeprecations.dev/api/v1/models/xai/grok-4-1-fast-reasoning.json