Model comparison
GPT-5.3 Codex vs Mercury 2.5
GPT-5.3 Codex is the stronger model overall, scoring 45.8 to 33.5 on the Noometry Index. Mercury 2.5 costs 71× less per token, which makes it the better buy when GPT-5.3 Codex's lead doesn't matter for your workload.
Last verified . 1 shared benchmarks.
Summary
- They share 1 benchmark with published results for both. GPT-5.3 Codex scores higher in 1 category and Mercury 2.5 in 0 categories; one gap is clear of the uncertainty.
- The widest gap is in coding, where GPT-5.3 Codex leads 48.6 to 39.5.
- Mercury 2.5 is cheaper at $0.04 / $0.15 per million input/output tokens, against $1.75 / $14 for GPT-5.3 Codex.
- GPT-5.3 Codex accepts more context: 400K tokens versus 260K.
Side by side
| GPT-5.3 Codex | Mercury 2.5 | |
|---|---|---|
| Provider | OpenAI | Inception |
| Noometry Index | 45.8 | 33.5 |
| Released | 2026-02-05 | 2026-09-08 |
| Weights | Proprietary | Proprietary |
| Context window | 400K | 260K |
| Max output | 128K | 66K |
| Input $ / M tokens | $1.75 | $0.04 |
| Output $ / M tokens | $14 | $0.15 |
| Results tracked | 8 | 4 |
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Category by category
Coding GPT-5.3 Codex leads
GPT-5.3 Codex: 48.6 (#56), Mercury 2.5: 39.5 (#156)
| Benchmark | GPT-5.3 Codex | Mercury 2.5 |
|---|---|---|
| ALE-Bench | 1,655 | 301.65 |
| SWE-bench Verified | 74.8% | — |
| LMArena WebDev | 1409 | — |
| SciCode | — | 38.5% |
| WeirdML | 79.3% | — |
Agentic & Tool Use Not comparable
GPT-5.3 Codex: 48.0 (#9), Mercury 2.5: —
| Benchmark | GPT-5.3 Codex | Mercury 2.5 |
|---|---|---|
| Terminal-Bench | 78.4% | — |
| METR Time Horizons | 74.5% | — |
| Vending-Bench 2 | 5,940 | — |
Reasoning Not comparable
GPT-5.3 Codex: —, Mercury 2.5: 22.4 (#193)
| Benchmark | GPT-5.3 Codex | Mercury 2.5 |
|---|---|---|
| CritPt | — | 0% |
| Epoch Capabilities Index | 156.77 | — |
Math Not comparable
GPT-5.3 Codex: —, Mercury 2.5: 23.3 (#272)
| Benchmark | GPT-5.3 Codex | Mercury 2.5 |
|---|---|---|
| ProofBench | — | 3% |
Frequently asked questions
Is GPT-5.3 Codex better than Mercury 2.5?
GPT-5.3 Codex is the stronger model overall, scoring 45.8 to 33.5 on the Noometry Index. Mercury 2.5 costs 71× less per token, which makes it the better buy when GPT-5.3 Codex's lead doesn't matter for your workload.
Which is cheaper, GPT-5.3 Codex or Mercury 2.5?
Mercury 2.5 is cheaper. It lists at $0.04 per million input tokens and $0.15 per million output tokens; GPT-5.3 Codex lists at $1.75 and $14.
Is GPT-5.3 Codex or Mercury 2.5 better for coding?
GPT-5.3 Codex scores higher on coding benchmarks: 48.6 versus 39.5 in the Noometry coding category.
Which has the bigger context window?
GPT-5.3 Codex does, with 400K tokens against 260K.
How many benchmarks do GPT-5.3 Codex and Mercury 2.5 share?
1 benchmark has published results for both models. GPT-5.3 Codex has 8 scored results on Noometry and Mercury 2.5 has 4.