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GPT-5.3 Codex vs o3
A detailed comparison of GPT-5.3 Codex (OpenAI) and o3 (OpenAI) across pricing, performance, and features.
Pricing Comparison
| Metric | GPT-5.3 Codex | o3 | Difference |
|---|---|---|---|
| Input / 1M tokens | $2.00 | $0.40 | -80% |
| Output / 1M tokens | $16.00 | $1.60 | -90% |
| Context window | 200K | 200K | — |
| Max output | 65.536K | 100K | — |
Benchmark Comparison
| Benchmark | GPT-5.3 Codex | o3 |
|---|---|---|
| MMLU-Pro | 90% | 87% |
| HumanEval | 96.5% | 94.5% |
| GPQA | 78% | 79.2% |
Capabilities
| Capability | GPT-5.3 Codex | o3 |
|---|---|---|
| code | ✓ | ✓ |
| reasoning | ✓ | ✓ |
| text | ✓ | ✓ |
| tool-use | ✓ | ✓ |
| vision | ✓ | ✓ |
GPT-5.3 Codex Strengths
- ✓Best coding model from OpenAI
- ✓Large output window (65K tokens)
- ✓Strong reasoning for complex tasks
GPT-5.3 Codex Weaknesses
- ✗API access not yet available
- ✗Premium pricing
o3 Strengths
- ✓Recently repriced — now very cheap
- ✓Excellent logical reasoning
- ✓200K context window
o3 Weaknesses
- ✗Slower due to reasoning overhead
- ✗Overkill for simple tasks
Quick Verdict
Best value: o3 is the more affordable option at $0.4/$1.6 per 1M tokens.
Higher benchmarks: GPT-5.3 Codex scores higher on average across available benchmarks (88.2% avg).
Choose o3 if cost matters most. Choose GPT-5.3 Codex if you need the best possible quality for complex tasks.