Model Details
o1
Quick answer: o1 is OpenAI's December 2024 reasoning model, the successor to the o1-preview. It scores 97.3% on GSM8K and 94.8% on the MATH benchmark, demonstrating strong quantitative reasoning. Priced at $15 input / $60 output per 1M tokens with a 200K-token context window. Succeeded by o3 (April 2025), which delivers substantially better performance at lower cost.
At a Glance
Where o1 leads
- 97.3% GSM8K — top-tier grade-school mathematics
- 94.8% MATH — strong competition math performance
- Pioneer of the o-series chain-of-thought paradigm
- Multimodal vision support
- 200K-token context window
Where it lags
- Superseded by o3 (April 2025), which is stronger across all benchmarks at lower cost ($10/$40 vs $15/$60)
- 7.96% Humanity's Last Exam — below subsequent o-series models
- Highest per-token price in the o-series
- Closed API model with no open weights
Best for: Teams with existing o1 integrations; historical reference; workflows where the specific o1 behaviour has been validated in production.
What o1 Is
o1 (December 2024) was OpenAI's first fully released o-series model, following the earlier o1-preview (September 2024). It introduced chain-of-thought reasoning to the mainstream OpenAI API: the model generates internal reasoning tokens before producing a final answer, improving accuracy on hard math, science, and coding tasks at the cost of higher latency and token usage.
At its December 2024 launch, o1 was state-of-the-art on competitive mathematics benchmarks (97.3% GSM8K, 94.8% MATH) and represented a step-change over GPT-4o for tasks requiring sustained multi-step reasoning. It established the o-series as OpenAI's primary line for hard reasoning tasks.
o1 was superseded by o3 in April 2025, which delivers materially stronger results across all benchmarks at a lower price ($10/$40 vs o1's $15/$60). For new integrations, o3 or o4-mini is the recommended choice. o1 remains available via the API for teams with existing validated deployments.
Specifications
| Field | Value |
|---|---|
| Organization | OpenAI |
| Parameters | Undisclosed |
| Context window | 200,000 tokens |
| Max output | 100,000 tokens |
| Architecture | Chain-of-thought reasoning (o-series) |
| License | Proprietary (API only) |
| Release date | December 17, 2024 |
| Knowledge cutoff | October 2023 |
| Modality | Text + Vision (multimodal) |
Pricing
| Input (per 1M tokens) | Output (per 1M tokens) | |
|---|---|---|
| OpenAI API | $15.00 | $60.00 |
Reasoning tokens are billed as output tokens. Pricing per OpenAI pricing page. Note: o3 provides better performance at $10/$40 per 1M.
Context Window
o1 has a 200,000-token context window — roughly 150 pages of text in a single request, matching o3 and o4-mini.
Public Benchmark Scores
| Benchmark | Score | Source | Date |
|---|---|---|---|
| GSM8K | 97.3% | Benchgen evaluation | 2025-07 |
| MATH | 94.8% | Benchgen evaluation | 2025-07 |
| Humanity's Last Exam | 7.96% | Benchgen evaluation | 2025-07 |
Scores from Benchgen evaluations. See the source for methodology.
o1 vs Alternatives
| Model | Context | GSM8K | MATH | Price (in/out per 1M) |
|---|---|---|---|---|
| o1 | 200K | 97.3% | 94.8% | $15 / $60 |
| o3 | 200K | — | — | $10 / $40 |
| o4-mini | 200K | — | — | $1.10 / $4.40 |
| DeepSeek R1 | 128K | — | — | ~$0.55 / $2.19 |
o3 and o4-mini both outperform o1 on modern benchmarks at lower cost. For new deployments, o4-mini is the recommended default; for maximum reasoning capability, o3 is the better choice.
Use o1 via API
from openai import OpenAI
client = OpenAI(api_key="YOUR_API_KEY")
response = client.chat.completions.create(
model="o1",
messages=[{"role": "user", "content": "Prove that the square root of 2 is irrational..."}],
)
print(response.choices[0].message.content)Related Models & Benchmarks
Frequently Asked Questions
What is o1?
o1 is OpenAI's December 2024 reasoning model, the first fully released member of the o-series. It uses chain-of-thought reasoning to achieve strong performance on math and science benchmarks. It has been superseded by o3 (April 2025), which is stronger and cheaper.What is o1's context window?
o1 supports a 200,000-token context window with up to 100,000 output tokens.How much does o1 cost?
o1 is priced at $15.00 per 1M input tokens and $60.00 per 1M output tokens. o3 provides better performance at $10/$40 per 1M and is the recommended alternative.Is o1 open source?
No. o1 is a proprietary, API-only model. There are no open weights.Should I use o1 or o3?
For new integrations, o3 is the better choice: it outperforms o1 on all benchmarks and costs $10/$40 per 1M (vs o1's $15/$60). o1 is appropriate only if you have an existing production deployment validated on o1-specific behaviour.Specs and scores sourced from OpenAI's official o1 announcement (December 17, 2024) and Benchgen evaluations. Pricing cited to the OpenAI pricing page. Last updated 2026-07-23.
Benchmark Leaderboards
This model isn’t on any benchmark leaderboard yet.