# xAI Grok 4 Fast Reasoning — deprecation status

> Yes — Grok 4 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.

The September 2025 model that introduced the 2M context window to the xAI API and undercut every comparable frontier model on price, which is why it ended up in so many agent frameworks as the default. Retired 15 May 2026, one generation behind 4.1 Fast and shut down on the same day as it.

## Facts

| Field | Value |
| --- | --- |
| Provider | xAI |
| Model id | `grok-4-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
  - Maps to grok-4.3 with reasoning effort "low".
  - Parameters it accepts: https://modelparams.dev/models/xai/grok-4.3

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

## FAQ

### When did xAI Grok 4 Fast Reasoning shut down?

xAI Grok 4 Fast Reasoning shut down on May 15, 2026. API requests to it fail from that date onward.

### What replaces xAI Grok 4 Fast Reasoning?

xAI recommends Grok 4.3 (`grok-4.3`) as the replacement for xAI Grok 4 Fast Reasoning. Maps to grok-4.3 with reasoning effort "low".

### Is xAI Grok 4 Fast Reasoning still available?

No. xAI Grok 4 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 Fast Reasoning to grok-4.3?

Swap the model id in your API call: replace "grok-4-fast-reasoning" with "grok-4.3". Maps to grok-4.3 with reasoning effort "low".

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