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GPT-6 Astra vs Grok-4 Fast Reasoning

Comparing GPT-6 Astra and Grok-4 Fast Reasoning across benchmarks, pricing, and capabilities.

OpenAI · xAI · Updated for 2026

Which is better?

GPT-6 Astra and Grok-4 Fast Reasoning trade strengths across price, capabilities, and technical limits. The better choice depends on the workload.

On price, Grok-4 Fast Reasoning is roughly 72.7x cheaper per token on a blended 3:1 input/output basis, which adds up quickly at production volume.

Grok-4 Fast Reasoning also accepts a larger context window (2,000,000 input tokens), making it the stronger choice for long documents and large codebases.

Based on current LLM Stats indexes, shared benchmarks, pricing, and model metadata for 2026.

Choose GPT-6 Astra

  • you want the most recent training data — it shipped Sep 2026

Choose Grok-4 Fast Reasoning

  • cost matters — it's about 72.7x cheaper per token
  • you process long inputs — it offers a 2,000,000 token context window

At a glance

The differences that matter most.

GPT-6 Astra
OpenAI
Grok-4 Fast Reasoning
xAI
Benchmark wins
—
—
Input price
$10.00 / M
$0.20 / M
Output price
$50.00 / M
$0.50 / M
Context window
1,050,000
2,000,000

Individual benchmarks

22 reported for GPT-6 Astra · 0 for Grok-4 Fast Reasoning

No common benchmarks found

GPT-6 Astra and Grok-4 Fast Reasoningdon't have any common benchmark datasets to compare. They may have been evaluated on different testing suites.

Human preference

Blind head-to-head votes and playground preference scores

Pricing Analysis

Price comparison per million tokens

Grok-4 Fast Reasoning costs less

For input processing, GPT-6 Astra ($10.00/1M tokens) is 50.0x more expensive than Grok-4 Fast Reasoning ($0.20/1M tokens).

For output processing, GPT-6 Astra ($50.00/1M tokens) is 100.0x more expensive than Grok-4 Fast Reasoning ($0.50/1M tokens).

In conclusion, GPT-6 Astra is more expensive than Grok-4 Fast Reasoning.*

* Using a 3:1 ratio of input to output tokens

Lowest available price from all providers
Fri Sep 04 2026 • llm-stats.com
OpenAI
GPT-6 Astra
Input tokens$10.00
Output tokens$50.00
Best providerOpenAI
xAI
Grok-4 Fast Reasoning
Input tokens$0.20
Output tokens$0.50
Best providerxAI
Notice missing or incorrect data?Start an Issue→

Context Window

Maximum input and output token capacity

Grok-4 Fast Reasoning accepts 2,000,000 input tokens compared to GPT-6 Astra's 1,050,000 tokens. GPT-6 Astra can generate longer responses up to 128,000 tokens, while Grok-4 Fast Reasoning is limited to 30,000 tokens.

OpenAI
GPT-6 Astra
Input1,050,000 tokens
Output128,000 tokens
xAI
Grok-4 Fast Reasoning
Input2,000,000 tokens
Output30,000 tokens
Fri Sep 04 2026 • llm-stats.com

Input capabilities

Documented input modalities across available providers

Both GPT-6 Astra and Grok-4 Fast Reasoning support multimodal inputs.

They are both capable of processing various types of data, offering versatility in application.

GPT-6 Astra

Text
Images
Audio
Video

Grok-4 Fast Reasoning

Text
Images
Audio
Video

License

Usage and distribution terms

Both models are licensed under proprietary licenses.

Both models have usage restrictions defined by their respective organizations.

GPT-6 Astra

Proprietary

Closed source

Grok-4 Fast Reasoning

Proprietary

Closed source

Release Timeline

When each model was launched

GPT-6 Astra was released on 2026-09-03, while Grok-4 Fast Reasoning was released on 2025-08-28.

GPT-6 Astra is 12 months newer than Grok-4 Fast Reasoning.

GPT-6 Astra

Sep 3, 2026

0 days ago

1.0yr newer
Grok-4 Fast Reasoning

Aug 28, 2025

1.0 years ago

Knowledge Cutoff

When training data ends

GPT-6 Astra has a documented knowledge cutoff of 2026-04-30, while Grok-4 Fast Reasoning's cutoff date is not specified.

We can confirm GPT-6 Astra's training data extends to 2026-04-30, but cannot make a direct comparison without Grok-4 Fast Reasoning's cutoff date.

GPT-6 Astra

Apr 2026

Grok-4 Fast Reasoning

—

Provider Availability

GPT-6 Astra is available from OpenAI. Grok-4 Fast Reasoning is available from xAI.

GPT-6 Astra

openai logo
OpenAI
Input Price:Input: $10.00/1MOutput Price:Output: $50.00/1M

Grok-4 Fast Reasoning

xai logo
xAI
Input Price:Input: $0.20/1MOutput Price:Output: $0.50/1M
* Prices shown are per million tokens

Outputs Comparison

Notice missing or incorrect data?Start an Issue discussion→

Judge for yourself.

Run your own prompts against GPT-6 Astra and Grok-4 Fast Reasoning side-by-side, then vote on the output you prefer.

GPT-6 Astra
✓ Preferred
Grok-4 Fast Reasoning
Open in Playground

FAQ

Common questions about GPT-6 Astra vs Grok-4 Fast Reasoning.

Which is better, GPT-6 Astra or Grok-4 Fast Reasoning?

GPT-6 Astra (OpenAI) and Grok-4 Fast Reasoning (xAI) each have strengths in different areas. Compare their benchmark scores, pricing, context windows, and capabilities above to determine which fits your needs.

How does GPT-6 Astra compare to Grok-4 Fast Reasoning in benchmarks?

GPT-6 Astra scores ExploitBench: 100.0%, ARC-AGI-3: 99.9%, ARC-AGI: 98.5%, FrontierMath Tier 4 (v2): 97.6%, GPQA: 96.0%.

Is GPT-6 Astra cheaper than Grok-4 Fast Reasoning?

Grok-4 Fast Reasoning is 50.0x cheaper for input tokens. GPT-6 Astra costs $10.00/M input and $50.00/M output via openai. Grok-4 Fast Reasoning costs $0.20/M input and $0.50/M output via xai.

What are the context window sizes for GPT-6 Astra and Grok-4 Fast Reasoning?

GPT-6 Astra supports 1.1M tokens and Grok-4 Fast Reasoning supports 2.0M tokens. A larger context window lets you process longer documents, conversations, or codebases in a single request.

What are the main differences between GPT-6 Astra and Grok-4 Fast Reasoning?

Key differences include context window (1.1M vs 2.0M), input pricing ($10.00 vs $0.20/M). See the full comparison above for benchmark-by-benchmark results.

Who makes GPT-6 Astra and Grok-4 Fast Reasoning?

GPT-6 Astra is developed by OpenAI and Grok-4 Fast Reasoning is developed by xAI.

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