# GPT-5.3 Codex vs Mercury 2

> GPT-5.3 Codex is the stronger model overall, scoring 45.5 to 38.8 on the Noometry Index. Mercury 2 costs 13× less per token, which makes it the better buy when GPT-5.3 Codex's lead doesn't matter for your workload.

- Canonical page: https://noometry.com/compare/gpt-5-3-codex-vs-mercury-2
- Last updated: 2026-10-10
- Shared benchmarks: 3

## Summary

- They share 3 benchmarks with published results for both. GPT-5.3 Codex scores higher in 1 category and Mercury 2 in 0 categories; one gap is clear of the uncertainty.
- The widest gap is in coding, where GPT-5.3 Codex leads 48.5 to 33.2.
- The biggest single-benchmark swing is WeirdML: 79.3% for GPT-5.3 Codex and 43.2% for Mercury 2.
- Mercury 2 is cheaper at $0.25 / $0.75 per million input/output tokens, against $1.75 / $14 for GPT-5.3 Codex.
- GPT-5.3 Codex accepts more context: 400K tokens versus 128K.

## Snapshot

| | GPT-5.3 Codex | Mercury 2 |
|---|---|---|
| Provider | OpenAI | Inception |
| Noometry Index | 45.5 | 38.8 |
| Rank | 61 | 167 |
| Context | 400K | 128K |
| Input $/M | $1.75 | $0.25 |
| Output $/M | $14 | $0.75 |
| Weights | Proprietary | Proprietary |

## Coding

- GPT-5.3 Codex: 48.5 (#51)
- Mercury 2: 33.2 (#250)

| Benchmark | GPT-5.3 Codex | Mercury 2 |
|---|---|---|
| LMArena WebDev | 1408 | 1170 |
| WeirdML | 79.3% | 43.2% |
| ALE-Bench | 1,655 | 785.58 |
| SWE-bench Verified | 74.8% | — |
| SciCode | — | 38.7% |
| LMArena Coding | — | 1391 |

## Agentic & Tool Use

- GPT-5.3 Codex: 47.8 (#9)
- Mercury 2: —

| Benchmark | GPT-5.3 Codex | Mercury 2 |
|---|---|---|
| Terminal-Bench | 78.4% | — |
| METR Time Horizons | 74.5% | — |
| Vending-Bench 2 | 5,940 | — |

## Reasoning

- GPT-5.3 Codex: —
- Mercury 2: 23.0 (#170)

| Benchmark | GPT-5.3 Codex | Mercury 2 |
|---|---|---|
| CritPt | — | 0.8% |
| LMArena Hard Prompts | — | 1362 |
| Epoch Capabilities Index | 156.84 | — |

## Knowledge

- GPT-5.3 Codex: —
- Mercury 2: 35.6 (#170)

| Benchmark | GPT-5.3 Codex | Mercury 2 |
|---|---|---|
| Vectara Hallucination Rate | — | 12.3% |
| LMArena Expert | — | 1358 |

## Multilingual

- GPT-5.3 Codex: —
- Mercury 2: 46.8 (#153)

| Benchmark | GPT-5.3 Codex | Mercury 2 |
|---|---|---|
| LMArena Non-English | — | 1331 |
| LMArena Chinese | — | 1416 |
| LMArena Russian | — | 1303 |

## Instruction Following

- GPT-5.3 Codex: —
- Mercury 2: 70.4 (#161)

| Benchmark | GPT-5.3 Codex | Mercury 2 |
|---|---|---|
| LMArena Instruction Following | — | 1328 |

## Long Context

- GPT-5.3 Codex: —
- Mercury 2: 40.4 (#149)

| Benchmark | GPT-5.3 Codex | Mercury 2 |
|---|---|---|
| LMArena Longer Query | — | 1329 |

## Writing & Preference

- GPT-5.3 Codex: —
- Mercury 2: 54.0 (#151)

| Benchmark | GPT-5.3 Codex | Mercury 2 |
|---|---|---|
| LMArena Text | — | 1355 |
| LMArena Creative Writing | — | 1289 |
| LMArena Multi-Turn | — | 1358 |

## FAQ

### Is GPT-5.3 Codex better than Mercury 2?

GPT-5.3 Codex is the stronger model overall, scoring 45.5 to 38.8 on the Noometry Index. Mercury 2 costs 13× 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?

Mercury 2 is cheaper. It lists at $0.25 per million input tokens and $0.75 per million output tokens; GPT-5.3 Codex lists at $1.75 and $14.

### Is GPT-5.3 Codex or Mercury 2 better for coding?

GPT-5.3 Codex scores higher on coding benchmarks: 48.5 versus 33.2 in the Noometry coding category.

### Which has the bigger context window?

GPT-5.3 Codex does, with 400K tokens against 128K.

### How many benchmarks do GPT-5.3 Codex and Mercury 2 share?

3 benchmarks have published results for both models. GPT-5.3 Codex has 8 scored results on Noometry and Mercury 2 has 17.