# GPT-5.3 Codex vs Mercury 2.5

> GPT-5.3 Codex has enough public results to be ranked (#61); Mercury 2.5 does not yet, so treat this comparison as directional.

- Canonical page: https://noometry.com/compare/gpt-5-3-codex-vs-mercury-2-5
- Last updated: 2026-10-10
- Shared benchmarks: 1

## Summary

- They share 1 benchmark with published results for both.
- 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.

## Snapshot

| | GPT-5.3 Codex | Mercury 2.5 |
|---|---|---|
| Provider | OpenAI | Inception |
| Noometry Index | 45.5 | 30.2 |
| Rank | 61 | — |
| Context | 400K | 260K |
| Input $/M | $1.75 | $0.04 |
| Output $/M | $14 | $0.15 |
| Weights | Proprietary | Proprietary |

## Coding

- GPT-5.3 Codex: 48.5 (#51)
- Mercury 2.5: —

| Benchmark | GPT-5.3 Codex | Mercury 2.5 |
|---|---|---|
| ALE-Bench | 1,655 | 301.65 |
| SWE-bench Verified | 74.8% | — |
| LMArena WebDev | 1408 | — |
| WeirdML | 79.3% | — |

## Agentic & Tool Use

- GPT-5.3 Codex: 47.8 (#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

- GPT-5.3 Codex: —
- Mercury 2.5: —

| Benchmark | GPT-5.3 Codex | Mercury 2.5 |
|---|---|---|
| Epoch Capabilities Index | 156.84 | — |

## Math

- GPT-5.3 Codex: —
- Mercury 2.5: 22.4

| Benchmark | GPT-5.3 Codex | Mercury 2.5 |
|---|---|---|
| ProofBench | — | 3% |

## FAQ

### Is GPT-5.3 Codex better than Mercury 2.5?

GPT-5.3 Codex has enough public results to be ranked (#61); Mercury 2.5 does not yet, so treat this comparison as directional.

### 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.

### 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 2.