Model Comparison
Grok-4.1 Fast Reasoning vs Jamba 1.5 LargeWhich is better in 2026?
Comparing Grok-4.1 Fast Reasoning and Jamba 1.5 Large across benchmarks, pricing, and capabilities.
Verdict: Grok-4.1 Fast Reasoning vs Jamba 1.5 Large — which is better?
Grok-4.1 Fast Reasoning (by xAI) and Jamba 1.5 Large (by AI21 Labs) are two of the AI models people compare most. Here is how they stack up on benchmarks, price and capabilities, and which one to pick in 2026.
On price, Grok-4.1 Fast Reasoning is roughly 12.7x cheaper per token on a blended 3:1 input/output basis, which adds up quickly at production volume.
Grok-4.1 Fast Reasoning also accepts a larger context window (2,000,000 input tokens), making it the stronger choice for long documents and large codebases.
Choose Grok-4.1 Fast Reasoning if…
- cost matters — it's about 12.7x cheaper per token
- you process long inputs — it offers a 2,000,000 token context window
- you want the most recent training data — it shipped Nov 2025
Choose Jamba 1.5 Large if…
- you need open weights you can self-host or fine-tune
Performance Benchmarks
Comparative analysis across standard metrics
Grok-4.1 Fast Reasoning and Jamba 1.5 Largedon't have any common benchmark datasets to compare. They may have been evaluated on different testing suites.
Arena Performance
Human preference votes
Pricing Analysis
Price comparison per million tokens
For input processing, Grok-4.1 Fast Reasoning ($0.20/1M tokens) is 10.0x cheaper than Jamba 1.5 Large ($2.00/1M tokens).
For output processing, Grok-4.1 Fast Reasoning ($0.50/1M tokens) is 16.0x cheaper than Jamba 1.5 Large ($8.00/1M tokens).
In conclusion, Jamba 1.5 Large is more expensive than Grok-4.1 Fast Reasoning.*
* Using a 3:1 ratio of input to output tokens
Context Window
Maximum input and output token capacity
Grok-4.1 Fast Reasoning accepts 2,000,000 input tokens compared to Jamba 1.5 Large's 256,000 tokens. Jamba 1.5 Large can generate longer responses up to 256,000 tokens, while Grok-4.1 Fast Reasoning is limited to 30,000 tokens.
Input Capabilities
Supported data types and modalities
Grok-4.1 Fast Reasoning supports multimodal inputs, whereas Jamba 1.5 Large does not.
Grok-4.1 Fast Reasoning can handle both text and other forms of data like images, making it suitable for multimodal applications.
Grok-4.1 Fast Reasoning
Jamba 1.5 Large
License
Usage and distribution terms
Grok-4.1 Fast Reasoning is licensed under a proprietary license, while Jamba 1.5 Large uses Jamba Open Model License.
License differences may affect how you can use these models in commercial or open-source projects.
Proprietary
Closed source
Jamba Open Model License
Open weights
Release Timeline
When each model was launched
Grok-4.1 Fast Reasoning was released on 2025-11-17, while Jamba 1.5 Large was released on 2024-08-22.
Grok-4.1 Fast Reasoning is 15 months newer than Jamba 1.5 Large.
Nov 17, 2025
8 months ago
1.2yr newerAug 22, 2024
1.9 years ago
Knowledge Cutoff
When training data ends
Jamba 1.5 Large has a documented knowledge cutoff of 2024-03-05, while Grok-4.1 Fast Reasoning's cutoff date is not specified.
We can confirm Jamba 1.5 Large's training data extends to 2024-03-05, but cannot make a direct comparison without Grok-4.1 Fast Reasoning's cutoff date.
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Mar 2024
Provider Availability
Grok-4.1 Fast Reasoning is available from xAI. Jamba 1.5 Large is available from Bedrock, Google.
Grok-4.1 Fast Reasoning
Jamba 1.5 Large
Outputs Comparison
Key Takeaways
Jamba 1.5 Large
View detailsAI21 Labs
Detailed Comparison
Interactive Arena
Judge for yourself.
Run your own prompts against Grok-4.1 Fast Reasoning and Jamba 1.5 Large side-by-side, then vote on the output you prefer.
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FAQ
Common questions about Grok-4.1 Fast Reasoning vs Jamba 1.5 Large.