o3 for reasoning
o3 is the #1 pick on LLMDex's llm for reasoning ranking out of 6 models we track for this use case. Below, the specific reasons it slots where it does, and when you should reach for an alternative.
Updated
At a glance
- Rank
- #1 of 6
- Context
- 200K tokens
- Output / 1M
- $8.00 / 1M tokens
- Released
- Apr 2025
Why o3 fits this task
Three things about o3 that map directly onto what this task rewards: Industry-leading reasoning depth at launch; Strong on math, science, and abstract puzzles; Tool-use during reasoning loops.
The criteria this task rewards
LLMDex ranks best llm for reasoning on 5 criteria , these are the axes the ranking uses, in priority order:
- GPQA Diamond performance
- ARC-AGI public set scores
- Chain-of-thought coherence on novel puzzles
- Reasoning-token cost, expensive on flagship reasoning models
- Latency budget, reasoning runs are slow by design
How o3 scores on each axis
Where o3 costs you: slow first-token, unpredictable total latency. For most teams this is acceptable on this workload, the value of the strengths above outweighs the cost. For cost-bound workloads or teams with strict latency budgets, run an eval against the next two ranked models on real data before committing.
Strengths that pay off here
- Industry-leading reasoning depth at launch
- Strong on math, science, and abstract puzzles
- Tool-use during reasoning loops
Tracked weaknesses
- Slow first-token, unpredictable total latency
- Expensive when reasoning runs long
When to pick something else
If you have a binding constraint that o3 doesn't satisfy, pricing, license, regional availability, modality coverage, the next-best pick on this task is GPT-5.5 from OpenAI. OpenAI's mid-cycle GPT-5 refresh, improved reasoning, tool use, and multimodal grounding over the 2025 launch.
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Other models for reasoning
- GPT-5.5 for reasoning
OpenAI's mid-cycle GPT-5 refresh, improved reasoning, tool use, and multimodal grounding over the 2025 launch.
Read guide - Claude Opus 4.7 for reasoning
Anthropic's mid-2026 flagship, ahead on SWE-bench, agent reliability, and writing quality.
Read guide - DeepSeek-R1 for reasoning
First open-weight reasoning model to match o1, the release that proved RL-from-scratch reasoning training was reproducible.
Read guide - Gemini 3 Pro for reasoning
Google's late-2025 flagship, set new benchmarks on long-context, vision, and reasoning at competitive pricing.
Read guide - o4 for reasoning
OpenAI's late-2025 standalone reasoning model, an evolution of o3 with deeper chain-of-thought and stronger multimodal reasoning.
Read guide
o3 for other use cases
Direct comparisons
Frequently asked
Is o3 good for reasoning?
o3 is ranked #1 on LLMDex's reasoning list. OpenAI's flagship reasoning model, set the bar for hard math, GPQA, and agent benchmarks in 2025.How much does o3 cost for reasoning?
o3 costs $2.00 / 1M tokens for input tokens and $8.00 / 1M tokens for output tokens. For reasoning workloads, output costs typically dominate; budget on the higher number.What's a cheaper alternative to o3 for reasoning?
The next ranked model on this task is GPT-5.5. Compare both before committing.When should I NOT use o3 for reasoning?
Tracked weakness: Slow first-token, unpredictable total latency. If that constraint is binding for your workload, the next-ranked model on this task is the safer pick.
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