Model Tracker
Grok 4 Fast
Grok 4 Fast is an AI model made by xAI. xAI released it on 19 September 2025. xAI retired it on 15 May 2026. Its context window is 2,000,000 tokens.
- Released
- 19 September 2025 — x.ai, read 16 October 2026
- Status
- Not confirmed: two readings disagree: retired and ga
- Takes
- Not confirmed: The maker's pages reviewed do not specify the model's input modalities.
- Returns
- Not confirmed: The maker's pages reviewed do not specify the model's output modalities.
- Open weights
- Not confirmed: The maker's pages reviewed do not state whether the model weights are open or provide downloadable weights.
- Licence
- Not confirmed: The maker's pages reviewed do not name a licence for the model.
- Context window
- 2,000,000 tokens — x.ai, read 16 October 2026
- Longest answer
- Not confirmed: The maker's pages reviewed do not print a standard maximum output-token limit for this model.
- Knowledge cutoff
- Not confirmed: The maker's pages reviewed do not state this model's knowledge cutoff.
- API price, input
- Not confirmed: The maker's current API pricing page does not list this retired model, so its standard input price cannot be confirmed from the required pricing page.
- API price, output
- Not confirmed: The maker's current API pricing page does not list this retired model, so its standard output price cannot be confirmed from the required pricing page.
- Where
- Not confirmed: The announcement records launch availability, but the maker's pages reviewed do not establish current availability across the listed channels after retirement.
- Parameters
- Not confirmed: The maker's pages reviewed do not publish the parameter count.
- Model card
- Not confirmed: two readings disagree: https://data.x.ai/2025-09-19-grok-4-fast-model-card.pdf and https://docs.x.ai/docs/models/grok-4-fast
Benchmarks
Measured by others, not by the maker: each score with the name the measurer gives the model and the setting it ran, its day and its licence.
Arena
- Text Arena, grok-4-fast-reasoning: 1,405 (1,400–1,410, 18,269 votes), published 15 October 2026
- Code Arena (WebDev), Grok 4 Fast (Reasoning): 1,160 (1,132–1,187, 743 votes), published 18 October 2026
Arena’s leaderboard dataset (lmarena-ai/leaderboard-dataset on Hugging Face), CC BY 4.0: ratings from people’s votes between two anonymous models, as Arena publishes them. Data · CC BY 4.0
Epoch AI
- Epoch Capabilities Index, Grok 4 Fast: 144.2 (142.0–146.4), as of 19 October 2026
Epoch AI, ‘Capabilities & benchmarking’, epoch.ai/benchmarks, CC BY 4.0: Epoch AI’s own runs and its Capabilities Index. Data · CC BY 4.0
Questions
When was Grok 4 Fast released?
xAI released Grok 4 Fast on 19 September 2025.
What is the context window of Grok 4 Fast?
The context window of Grok 4 Fast is 2,000,000 tokens, as xAI prints it.
More from xAI
- Grok 3
- Grok 3 (Think)
- Grok 3 mini
- Grok 3 mini (Think)
- Grok 4
- Grok 4 Heavy
- Grok 4.1
- Grok 4.1 Fast
- Grok 4.20
- Grok 4.20 Multi-Agent Beta
- Grok 4.3
- Grok 4.5
- Grok 4.6
- Grok 4.7
- Grok Build 0.1
- Grok Code Fast 1
- Grok Imagine Image 2.0
- Grok Imagine Video 1.5
- Grok Voice 1.0
- Grok Voice 2.0
- Grok Voice 3.0
- Grok-1
- Grok-1.5V
- Grok-2
Sources
- Grok 4 Fast (read 16 October 2026)
- Grok 4 Fast Model Card (read 16 October 2026)
- May 15, 2026 Model Retirement (read 16 October 2026)
- API Pricing (read 16 October 2026)