News20 Dec 20257 min read

OpenAI o3: The Reasoning Model That Thinks Before Answering

OpenAI's o3 model achieves 87.7% on GPQA Diamond and 96.7% on AIME 2024 through extended chain-of-thought reasoning, redefining what's possible in AI problem-solving.

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Max Beech
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TL;DR

  • o3 achieves PhD-level performance on science/math benchmarks via extended reasoning.
  • Spends 10-60 seconds thinking before answering complex questions.
  • 3 reasoning modes: low ($5/$15), medium ($15/$60), high ($50/$200 per million tokens).
  • Best for: research, advanced problem-solving, code generation requiring deep analysis.

OpenAI o3: The Reasoning Model That Thinks Before Answering

OpenAI released o3 in December 2024, following o1 with even more sophisticated reasoning capabilities. Unlike standard models that generate answers immediately, o3 deliberates -spending seconds or minutes working through problems step-by-step before responding. This "thinking time" enables PhD-level performance on complex reasoning tasks previously beyond AI capabilities.

For applications requiring rigorous problem-solving -scientific research, advanced mathematics, complex code generation -o3 represents a capability leap.

Benchmark performance

Benchmarko3 (high)o1GPT-4oHuman expert
GPQA Diamond (PhD science)87.7%78.3%56.1%69.7%
AIME 2024 (math competition)96.7%83.3%13.4%~60%
Codeforces (competitive programming)2727 Elo1891 Elo808 Elo1500-1800
HumanEval (code generation)96.7%92.0%90.2%N/A

o3 surpasses human PhD holders on science questions and matches top competitive programmers.

"Focus is the ultimate competitive advantage. The companies that win are the ones saying no to 99% of opportunities to double down on the 1% that matters." - Naval Ravikant, Founder of AngelList

How reasoning works

Traditional models (GPT-4o)

User: "Solve this differential equation..."
Model: [Generates answer immediately]
Latency: 0.8s

Reasoning models (o3)

User: "Solve this differential equation..."
Model: [Thinks for 15s]
  - Analyzing equation structure
  - Considering integration methods
  - Testing substitution approach
  - Verifying boundary conditions
  - Double-checking algebra
[Generates answer]
Latency: 15.4s

Trade-off: 10-20× longer latency for significantly higher accuracy on complex problems.

Reasoning modes

ModeThinking timeAccuracy gainPrice (input/output)
Low5-10s+15% vs GPT-4o$5/$15 per M tokens
Medium20-40s+35% vs GPT-4o$15/$60 per M tokens
High60-300s+50% vs GPT-4o$50/$200 per M tokens

Choose based on problem complexity and latency tolerance.

Use cases

1. Scientific research

Task: "Propose experimental design to test [hypothesis]"

o3 approach:

  • Reviews relevant literature
  • Considers confounding variables
  • Designs control groups
  • Predicts statistical power
  • Suggests equipment and methodology

Output quality: Comparable to postdoc-level experimental design.

2. Advanced code generation

Task: "Implement a distributed consensus algorithm"

o3 reasoning:

  • Analyzes CAP theorem implications
  • Considers failure modes
  • Designs message passing protocol
  • Implements with correctness proofs
  • Generates comprehensive tests

Result: Production-ready code with edge cases handled.

3. Mathematical proofs

Task: "Prove [complex theorem]"

o3 process:

  • Explores proof strategies
  • Tests lemmas
  • Identifies contradictions
  • Constructs rigorous argument
  • Verifies logical consistency

Production considerations

When to use o3

Choose o3 if:

  • Problem requires deep reasoning (math, science, complex logic)
  • Accuracy more important than latency
  • Budget allows premium pricing
  • Single high-quality answer preferred over multiple attempts

Choose GPT-4o if:

  • Need sub-second responses
  • Task is straightforward (chat, content generation)
  • Volume-sensitive pricing
  • "Good enough" answers acceptable

Cost comparison

Scenario: Generate solution to competitive programming problem

ApproachSuccess rateAttempts neededTotal cost
GPT-4o (multiple attempts)25%4$0.08
o3 low (single attempt)70%1.4$0.35
o3 high (single attempt)95%1.05$1.50

o3 high costs more but often cheaper overall due to higher first-attempt success rate.

Call-to-action (Awareness stage) Test o3's reasoning on complex problems in the OpenAI Playground (select o3 model).

FAQs

Why is it called o3 not o2?

OpenAI skipped "o2" to avoid trademark conflicts with UK telecom company O2.

Can I see the reasoning process?

Not in API currently -thinking is internal. Visible in Playground for debugging.

Does it support function calling?

Yes, can invoke tools during reasoning process.

What's the maximum thinking time?

Configurable up to 5 minutes in high mode; auto-stops if solution found earlier.

Is it available via API?

Yes, generally available as o3 model ID.

Summary

OpenAI o3 achieves breakthrough performance on complex reasoning tasks by spending extended time deliberating before answering. Best suited for scientific research, advanced mathematics, and sophisticated code generation where accuracy justifies 10-20× higher latency and cost. Standard models remain better for conversational AI and simple tasks.

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