Best AI model for reasoning — September 2026
On BenchLM's public evidence, GPT-6 Astra has the highest reasoning score estimate among the models that meet this page's constraints (89.5). Reasoning evidence is limited and includes specific long-context and abstract tasks.
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The shortlist for reasoning
Constraints on this page: a builder choosing by accuracy, hosted processing allowed, any price, ordinary input size. Change any of them under Refine. A small score gap does not establish a reliably better model.
Compare GPT-6 Astra vs Claude Fable 5.1Full reasoning leaderboard
01GPT-6 AstraBest fit
OpenAI · Proprietary
89.5
Reasoning score estimate
- Highest reasoning estimate among models that meet every stated constraint
- $20.00 for the stated workload
- 1.05M context
02Claude Fable 5.1
Anthropic · Proprietary
79.4
Reasoning score estimate
- Estimate 79.4 on the same reasoning evidence
- $20.00 for the stated workload
- 1M context
03Kimi K3
Moonshot AI · Pending
78.5
Reasoning score estimate
- Estimate 78.5 on the same reasoning evidence
- $6.00 for the stated workload
- 1.05M context
04MiniMax M3
MiniMax · Open Weight
78.0
Reasoning score estimate
- Estimate 78.0 on the same reasoning evidence
- $0.54 for the stated workload
- 1M context
- Open weights, so it can run on your own hardware
05Muse Spark 1.3
Meta · Proprietary
78.0
Reasoning score estimate
- Estimate 78.0 on the same reasoning evidence
- $2.10 for the stated workload
- 1M context
Refine for your situation
Each link opens the selector with one answer changed. The address carries the answers, so your version is as shareable as this page.
What this shortlist rests on
The reasoning surface. The category score is a weighted average of these public benchmarks.
- 25%ARC-AGI-2Current
- 25%LongBench v2Current
- 20%MRCRv2Current
- 15%AA-LCRCurrent
- 15%ARC-AGI-3Current
What to verify before choosing
- Reasoning evidence is limited and includes specific long-context and abstract tasks.
- Composite scores are estimates. A small score gap does not establish a reliably better model.
Try three representative examples of your own work. Compare errors, time, cost, and the tools available in your actual setup.
Questions
Which AI model is best for reasoning?
On BenchLM's public evidence, GPT-6 Astra by OpenAI has the highest reasoning score estimate among models that meet the page's default constraints (89.5). Ordered by task score under the stated constraints. Reasoning evidence is limited and includes specific long-context and abstract tasks.
What are the alternatives to GPT-6 Astra for reasoning?
Claude Fable 5.1 (79.4), Kimi K3 (78.5), MiniMax M3 (78.0), Muse Spark 1.3 (78.0) follow on the same evidence. A small gap does not establish a reliably better model; compare them on three representative examples of your own work.
How does BenchLM pick the best ai model for reasoning?
The page runs the LLM Selector with fixed answers: a builder choosing by accuracy, hosted processing allowed, any price, ordinary input size. The selector uses the reasoning evidence surface, filters by the stated constraints, and orders by that evidence. It never adds a hidden fit score or a bonus for open weights or reasoning style.
Can I change the constraints?
Yes. Every link under "Refine" opens the selector with one answer changed, and the address carries the answers so a result can be shared or reopened against the current dataset.
Method: bench-align-v5.5-2026-09-04. Read the methodology and benchmark confidence pages for how scores and verification statuses are produced.
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