# GPT-5.1-Codex vs Mercury 2.5

> GPT-5.1-Codex is the stronger model overall, scoring 38.6 to 33.5 on the Noometry Index. Mercury 2.5 costs 51× less per token, which makes it the better buy when GPT-5.1-Codex's lead doesn't matter for your workload.

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

## Summary

- They share 2 benchmarks with published results for both. GPT-5.1-Codex scores higher in 2 categories and Mercury 2.5 in 0 categories; 2 gaps are clear of the uncertainty.
- The widest gap is in math, where GPT-5.1-Codex leads 30.3 to 23.3.
- The biggest single-benchmark swing is ProofBench: 9% for GPT-5.1-Codex and 3% for Mercury 2.5.
- Mercury 2.5 is cheaper at $0.04 / $0.15 per million input/output tokens, against $1.25 / $10 for GPT-5.1-Codex.
- GPT-5.1-Codex accepts more context: 400K tokens versus 260K.

## Snapshot

| | GPT-5.1-Codex | Mercury 2.5 |
|---|---|---|
| Provider | OpenAI | Inception |
| Noometry Index | 38.6 | 33.5 |
| Rank | 186 | 242 |
| Context | 400K | 260K |
| Input $/M | $1.25 | $0.04 |
| Output $/M | $10 | $0.15 |
| Weights | Proprietary | Proprietary |

## Coding

- GPT-5.1-Codex: 41.9 (#116)
- Mercury 2.5: 39.5 (#156)

| Benchmark | GPT-5.1-Codex | Mercury 2.5 |
|---|---|---|
| ALE-Bench | 1,245 | 301.65 |
| SWE-bench Verified (bash only) | 66% | — |
| LMArena WebDev | 1337 | — |
| SciCode | — | 38.5% |

## Agentic & Tool Use

- GPT-5.1-Codex: 38.0 (#33)
- Mercury 2.5: —

| Benchmark | GPT-5.1-Codex | Mercury 2.5 |
|---|---|---|
| Terminal-Bench | 60.4% | — |
| METR Time Horizons | 70.8% | — |

## Reasoning

- GPT-5.1-Codex: —
- Mercury 2.5: 22.4 (#193)

| Benchmark | GPT-5.1-Codex | Mercury 2.5 |
|---|---|---|
| CritPt | — | 0% |

## Math

- GPT-5.1-Codex: 30.3 (#235)
- Mercury 2.5: 23.3 (#272)

| Benchmark | GPT-5.1-Codex | Mercury 2.5 |
|---|---|---|
| ProofBench | 9% | 3% |

## FAQ

### Is GPT-5.1-Codex better than Mercury 2.5?

GPT-5.1-Codex is the stronger model overall, scoring 38.6 to 33.5 on the Noometry Index. Mercury 2.5 costs 51× less per token, which makes it the better buy when GPT-5.1-Codex's lead doesn't matter for your workload.

### Which is cheaper, GPT-5.1-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-5.1-Codex lists at $1.25 and $10.

### Is GPT-5.1-Codex or Mercury 2.5 better for coding?

GPT-5.1-Codex scores higher on coding benchmarks: 41.9 versus 39.5 in the Noometry coding category.

### Which has the bigger context window?

GPT-5.1-Codex does, with 400K tokens against 260K.

### How many benchmarks do GPT-5.1-Codex and Mercury 2.5 share?

2 benchmarks have published results for both models. GPT-5.1-Codex has 6 scored results on Noometry and Mercury 2.5 has 4.