Model comparison
GPT-5 Nano vs Mercury 2.5
GPT-5 Nano and Mercury 2.5 score almost the same on the Noometry Index (33.5 vs 33.5), so choose on price, context window or the category you care about most.
Last verified . 2 shared benchmarks.
Summary
- They share 2 benchmarks with published results for both. GPT-5 Nano scores higher in 1 category and Mercury 2.5 in 2 categories; 3 gaps are clear of the uncertainty.
- The widest gap is in reasoning, where Mercury 2.5 leads 22.4 to 16.3.
- The biggest single-benchmark swing is ProofBench: 12% for GPT-5 Nano and 3% for Mercury 2.5.
- Mercury 2.5 is cheaper at $0.04 / $0.15 per million input/output tokens, against $0.05 / $0.40 for GPT-5 Nano.
- GPT-5 Nano accepts more context: 400K tokens versus 260K.
Side by side
| GPT-5 Nano | Mercury 2.5 | |
|---|---|---|
| Provider | OpenAI | Inception |
| Noometry Index | 33.5 | 33.5 |
| Released | 2025-08-07 | 2026-09-08 |
| Weights | Proprietary | Proprietary |
| Context window | 400K | 260K |
| Max output | 128K | 66K |
| Input $ / M tokens | $0.05 | $0.04 |
| Output $ / M tokens | $0.40 | $0.15 |
| Results tracked | 49 | 4 |
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Category by category
Coding Mercury 2.5 leads
GPT-5 Nano: 33.6 (#254), Mercury 2.5: 39.5 (#156)
| Benchmark | GPT-5 Nano | Mercury 2.5 |
|---|---|---|
| ALE-Bench | 718.67 | 301.65 |
| SWE-bench Verified (bash only) | 34.8% | — |
| SciCode | — | 38.5% |
| WeirdML | 38.1% | — |
| LMArena Coding | 1351 | — |
Agentic & Tool Use Not comparable
GPT-5 Nano: 25.8 (#106), Mercury 2.5: —
| Benchmark | GPT-5 Nano | Mercury 2.5 |
|---|---|---|
| Terminal-Bench | 21.8% | — |
| Berkeley Function Calling Leaderboard | 51.5% | — |
Reasoning Mercury 2.5 leads
GPT-5 Nano: 16.3 (#306), Mercury 2.5: 22.4 (#193)
| Benchmark | GPT-5 Nano | Mercury 2.5 |
|---|---|---|
| ARC-AGI-2 | 2.6% | — |
| Kagi LLM Benchmark | 62.2% | — |
| ARC-AGI-1 | 20.7% | — |
| CritPt | — | 0% |
| Chess Puzzles | 27% | — |
| LMArena Hard Prompts | 1328 | — |
| Mystery Game Puzzles | 9% | — |
| DTBench | 62.7% | — |
| LMCA | 7.9% | — |
| Epoch Capabilities Index | 139.38 | — |
| ForecastBench | 59.1 | — |
Math GPT-5 Nano leads
GPT-5 Nano: 29.4 (#241), Mercury 2.5: 23.3 (#272)
| Benchmark | GPT-5 Nano | Mercury 2.5 |
|---|---|---|
| ProofBench | 12% | 3% |
| FrontierMath (Tiers 1-3) | 20% | — |
| FrontierMath Tier 4 | 2.4% | — |
| OTIS Mock AIME 2024-2025 | 81.1% | — |
| Omni-MATH | 54.6% | — |
| LMArena Math | 1317 | — |
| MATH Level 5 | 95.2% | — |
| FrontierMath (Feb 2025 set) | 8.3% | — |
| FrontierMath Tier 4 (v1) | 2.1% | — |
Knowledge Not comparable
GPT-5 Nano: 35.9 (#178), Mercury 2.5: —
| Benchmark | GPT-5 Nano | Mercury 2.5 |
|---|---|---|
| GPQA Diamond | 69.4% | — |
| SimpleQA Verified | 11.7% | — |
| MMLU-Pro | 77.8% | — |
| Vectara Hallucination Rate | 10.5% | — |
| GPQA (HELM) | 67.9% | — |
| LMArena Expert | 1321 | — |
Multimodal Not comparable
GPT-5 Nano: 31.3 (#108), Mercury 2.5: —
| Benchmark | GPT-5 Nano | Mercury 2.5 |
|---|---|---|
| LMArena Vision | 1159 | — |
| VPCT | 37.2% | — |
Multilingual Not comparable
GPT-5 Nano: 45.3 (#172), Mercury 2.5: —
| Benchmark | GPT-5 Nano | Mercury 2.5 |
|---|---|---|
| LMArena Non-English | 1313 | — |
| LMArena Chinese | 1356 | — |
| LMArena German | 1327 | — |
| LMArena Japanese | 1226 | — |
| LMArena Korean | 1269 | — |
| LMArena Russian | 1296 | — |
| LMArena Spanish | 1360 | — |
Instruction Following Not comparable
GPT-5 Nano: 75.0 (#79), Mercury 2.5: —
| Benchmark | GPT-5 Nano | Mercury 2.5 |
|---|---|---|
| IFEval | 93.2% | — |
| LMArena Instruction Following | 1306 | — |
Long Context Not comparable
GPT-5 Nano: 31.3 (#281), Mercury 2.5: —
| Benchmark | GPT-5 Nano | Mercury 2.5 |
|---|---|---|
| Fiction.LiveBench | 44.4% | — |
| LMArena Longer Query | 1312 | — |
Writing & Preference Not comparable
GPT-5 Nano: 39.1 (#249), Mercury 2.5: —
| Benchmark | GPT-5 Nano | Mercury 2.5 |
|---|---|---|
| LMArena Text | 1320 | — |
| LMArena Creative Writing | 1249 | — |
| EQ-Bench Creative Writing | 705 | — |
| WildBench | 80.6% | — |
| LMArena Multi-Turn | 1311 | — |
Frequently asked questions
Is GPT-5 Nano better than Mercury 2.5?
GPT-5 Nano and Mercury 2.5 score almost the same on the Noometry Index (33.5 vs 33.5), so choose on price, context window or the category you care about most.
Which is cheaper, GPT-5 Nano 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 Nano lists at $0.05 and $0.40.
Is GPT-5 Nano or Mercury 2.5 better for coding?
Mercury 2.5 scores higher on coding benchmarks: 39.5 versus 33.6 in the Noometry coding category.
Which has the bigger context window?
GPT-5 Nano does, with 400K tokens against 260K.
How many benchmarks do GPT-5 Nano and Mercury 2.5 share?
2 benchmarks have published results for both models. GPT-5 Nano has 49 scored results on Noometry and Mercury 2.5 has 4.