Model comparison
GPT-5.3 Codex vs o3-mini
Head-to-head evidence from 6 shared benchmark results across 3 categories. Overall scores shown here use the public BenchAlign v5 ranking lane.
Public leaderboard positions: GPT-5.3 Codex #29 (Supported); o3-mini #143 (Supported). Intervals and evidence labels describe ranking uncertainty, not a guarantee for a specific workload.
Evidence parity. GPT-5.3 Codex and o3-mini share 6 comparable benchmark results. 1 of 8 categories are comparable. 15 results are unique to GPT-5.3 Codex; 4 to o3-mini.
Updated July 24, 2026- Shared results
- 6
- GPT-5.3 Codex only
- 15
- o3-mini only
- 4
- Comparable categories
- 1 / 8
Pick GPT-5.3 Codex if you want the stronger benchmark profile. o3-mini only becomes the better choice if you want the cheaper token bill.
Confidence note. This is a partial-evidence comparison with 6 shared benchmark results across 3 evidence categories; 1 of 8 categories currently have scoreable aggregates for both models. Treat the verdict as directional until coverage is more balanced.
Why this result
GPT-5.3 Codex is clearly ahead on the BenchAlign aggregate, 66.18 to 46.73. The gap is large enough that you do not need to squint at the spreadsheet to see the difference.
GPT-5.3 Codex's sharpest advantage is in coding, where it averages 67.2 against 49.3. The single biggest benchmark swing on the page is SWE-bench Verified, 85% to 49.3%.
GPT-5.3 Codex is also the more expensive model on tokens at $1.75 input / $14.00 output per 1M tokens, versus $1.10 input / $4.40 output per 1M tokens for o3-mini. That is roughly 3.2x on output cost alone. GPT-5.3 Codex gives you the larger context window at 400K, compared with 200K for o3-mini.
Category breakdown
Exact category averages are shown below. Not measured means BenchLM does not have enough sourced public coverage for that model and category.
| Category | GPT-5.3 Codex | Δ | o3-mini |
|---|---|---|---|
| Coding | GPT-5.3 Codex67.2 | Margin← 17.9 | o3-mini49.3 |
| Agentic | GPT-5.3 Codex71.4 | MarginNo overlap | o3-miniNot measured |
| Knowledge | GPT-5.3 CodexNot measured | MarginNo overlap | o3-mini77.2 |
| Inst. Following | GPT-5.3 CodexNot measured | MarginNo overlap | o3-mini93.9 |
Decisive benchmark drivers
The largest measured benchmark gaps in this matchup, with exact reported values.
More
- Source ↗
SWE-bench Verified
CodingA 85%B 49.3%Winner: GPT-5.3 CodexΔ 35.7SWE-bench Verified: GPT-5.3 Codex scored 85%; o3-mini scored 49.3%. GPT-5.3 Codex wins this benchmark.
Operational comparison
Runtime and commercial metrics are compared only when both models have a complete sourced value.
| Metric | GPT-5.3 Codex | o3-mini | Comparison |
|---|---|---|---|
| Input / output priceUSD per 1M tokens | GPT-5.3 Codex$1.75 input / $14 output | o3-mini$1.1 input / $4.4 output | o3-mini has the lower combined listed price. |
| Generation speedtokens per second | GPT-5.3 Codex79 tok/s | o3-mini160 tok/s | o3-mini has the higher measured throughput. |
| First-answer latencyseconds to first token | GPT-5.3 Codex88.26 s | o3-mini7.12 s | o3-mini reaches the first token sooner. |
| Context windowmaximum listed tokens | GPT-5.3 Codex400K | o3-mini200K | GPT-5.3 Codex lists the larger context window. |
Benchmark Deep Dive
Agentic5 benchmarks
CodingGPT-5.3 Codex wins5 benchmarks
Reasoning2 benchmarks
Knowledge8 benchmarks
| Benchmark | GPT-5.3 Codex | o3-mini | Result |
|---|---|---|---|
| Artificial Analysis Intelligence IndexSource | 44.3% | 19.0% | GPT-5.3 Codex leads |
| AA-GPQA DiamondSource | 91.5% | 74.8% | GPT-5.3 Codex leads |
| AA-HLESource | 39.9% | 8.7% | GPT-5.3 Codex leads |
| AA-Omniscience IndexSource | 9.9% | — | Not comparable |
| AA-Omniscience AccuracySource | 51.8% | — | Not comparable |
| AA-Omniscience Hallucination RateSource | 86.9% | — | Not comparable |
| MMLUSource | — | 86.9% | Not comparable |
| GPQASource | — | 77.2% | Not comparable |
Math1 benchmarks
| Benchmark | GPT-5.3 Codex | o3-mini | Result |
|---|---|---|---|
| AIME 2024Source | — | 87.3% | Not comparable |
Multimodal2 benchmarks
Frequently Asked Questions (2)
Which is better, GPT-5.3 Codex or o3-mini?
GPT-5.3 Codex is ahead on BenchLM's BenchAlign leaderboard, 66.18 to 46.73. The biggest single separator in this matchup is SWE-bench Verified, where the scores are 85% and 49.3%.
Which is better for coding, GPT-5.3 Codex or o3-mini?
GPT-5.3 Codex has the edge for coding in this comparison, averaging 67.2 versus 49.3. Inside this category, SWE-bench Verified is the benchmark that creates the most daylight between them.