Model comparison
GPT-5-Codex vs Mercury 2
Mercury 2 is the stronger model overall, scoring 39.1 to 37.9 on the Noometry Index.
Last verified . 1 shared benchmarks.
Summary
- They share 1 benchmark with published results for both. GPT-5-Codex scores higher in 2 categories and Mercury 2 in 0 categories; 2 gaps are clear of the uncertainty.
- The widest gap is in coding, where GPT-5-Codex leads 42.4 to 33.5.
- The biggest single-benchmark swing is WeirdML: 54.5% for GPT-5-Codex and 43.2% for Mercury 2.
- Mercury 2 is cheaper at $0.25 / $0.75 per million input/output tokens, against $1.25 / $10 for GPT-5-Codex.
- GPT-5-Codex accepts more context: 400K tokens versus 128K.
Side by side
| GPT-5-Codex | Mercury 2 | |
|---|---|---|
| Provider | OpenAI | Inception |
| Noometry Index | 37.9 | 39.1 |
| Released | 2025-09-15 | 2026-02-20 |
| Weights | Proprietary | Proprietary |
| Context window | 400K | 128K |
| Max output | 128K | 50K |
| Input $ / M tokens | $1.25 | $0.25 |
| Output $ / M tokens | $10 | $0.75 |
| Results tracked | 3 | 17 |
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Category by category
Coding GPT-5-Codex leads
GPT-5-Codex: 42.4 (#103), Mercury 2: 33.5 (#255)
| Benchmark | GPT-5-Codex | Mercury 2 |
|---|---|---|
| WeirdML | 54.5% | 43.2% |
| LMArena WebDev | — | 1171 |
| SciCode | — | 38.7% |
| LMArena Coding | — | 1391 |
| ALE-Bench | — | 785.58 |
Agentic & Tool Use Not comparable
GPT-5-Codex: 31.0 (#72), Mercury 2: —
| Benchmark | GPT-5-Codex | Mercury 2 |
|---|---|---|
| Terminal-Bench | 44.3% | — |
Reasoning GPT-5-Codex leads
GPT-5-Codex: 30.9 (#83), Mercury 2: 23.8 (#170)
| Benchmark | GPT-5-Codex | Mercury 2 |
|---|---|---|
| Kagi LLM Benchmark | 70.3% | — |
| CritPt | — | 0.8% |
| LMArena Hard Prompts | — | 1362 |
Knowledge Not comparable
GPT-5-Codex: —, Mercury 2: 36.2 (#172)
| Benchmark | GPT-5-Codex | Mercury 2 |
|---|---|---|
| Vectara Hallucination Rate | — | 12.3% |
| LMArena Expert | — | 1358 |
Multilingual Not comparable
GPT-5-Codex: —, Mercury 2: 46.6 (#157)
| Benchmark | GPT-5-Codex | Mercury 2 |
|---|---|---|
| LMArena Non-English | — | 1331 |
| LMArena Chinese | — | 1417 |
| LMArena Russian | — | 1304 |
Instruction Following Not comparable
GPT-5-Codex: —, Mercury 2: 70.2 (#165)
| Benchmark | GPT-5-Codex | Mercury 2 |
|---|---|---|
| LMArena Instruction Following | — | 1329 |
Long Context Not comparable
GPT-5-Codex: —, Mercury 2: 40.5 (#154)
| Benchmark | GPT-5-Codex | Mercury 2 |
|---|---|---|
| LMArena Longer Query | — | 1330 |
Writing & Preference Not comparable
GPT-5-Codex: —, Mercury 2: 53.8 (#155)
| Benchmark | GPT-5-Codex | Mercury 2 |
|---|---|---|
| LMArena Text | — | 1355 |
| LMArena Creative Writing | — | 1289 |
| LMArena Multi-Turn | — | 1358 |
Frequently asked questions
Is GPT-5-Codex better than Mercury 2?
Mercury 2 is the stronger model overall, scoring 39.1 to 37.9 on the Noometry Index.
Which is cheaper, GPT-5-Codex or Mercury 2?
Mercury 2 is cheaper. It lists at $0.25 per million input tokens and $0.75 per million output tokens; GPT-5-Codex lists at $1.25 and $10.
Is GPT-5-Codex or Mercury 2 better for coding?
GPT-5-Codex scores higher on coding benchmarks: 42.4 versus 33.5 in the Noometry coding category.
Which has the bigger context window?
GPT-5-Codex does, with 400K tokens against 128K.
How many benchmarks do GPT-5-Codex and Mercury 2 share?
1 benchmark has published results for both models. GPT-5-Codex has 3 scored results on Noometry and Mercury 2 has 17.