Model comparison
Mercury 2.5 vs Step 5 Preview
Step 5 Preview is the stronger model overall, scoring 47.9 to 33.5 on the Noometry Index. Mercury 2.5 costs 21× less per token, which makes it the better buy when Step 5 Preview's lead doesn't matter for your workload.
Last verified . 3 shared benchmarks.
StepFunSummary
- They share 3 benchmarks with published results for both. Mercury 2.5 scores higher in 0 categories and Step 5 Preview in 3 categories; 3 gaps are clear of the uncertainty.
- The widest gap is in math, where Step 5 Preview leads 46.1 to 23.3.
- The biggest single-benchmark swing is ProofBench: 3% for Mercury 2.5 and 42% for Step 5 Preview.
- Mercury 2.5 is cheaper at $0.04 / $0.15 per million input/output tokens, against $1 / $2.70 for Step 5 Preview.
- Step 5 Preview accepts more context: 1.02M tokens versus 260K.
Side by side
| Mercury 2.5 | Step 5 Preview | |
|---|---|---|
| Provider | Inception | StepFun |
| Noometry Index | 33.5 | 47.9 |
| Released | 2026-09-08 | 2026-09-16 |
| Weights | Proprietary | Proprietary |
| Context window | 260K | 1.02M |
| Max output | 66K | 66K |
| Input $ / M tokens | $0.04 | $1 |
| Output $ / M tokens | $0.15 | $2.70 |
| Results tracked | 4 | 18 |
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Category by category
Coding Step 5 Preview leads
Mercury 2.5: 39.5 (#156), Step 5 Preview: 51.8 (#36)
| Benchmark | Mercury 2.5 | Step 5 Preview |
|---|---|---|
| SciCode | 38.5% | 58.9% |
| LMArena WebDev | — | 1564 |
| LMArena Coding | — | 1480 |
| ALE-Bench | 301.65 | — |
Reasoning Step 5 Preview leads
Mercury 2.5: 22.4 (#193), Step 5 Preview: 40.0 (#57)
| Benchmark | Mercury 2.5 | Step 5 Preview |
|---|---|---|
| CritPt | 0% | 20.9% |
| LMArena Hard Prompts | — | 1465 |
Math Step 5 Preview leads
Mercury 2.5: 23.3 (#272), Step 5 Preview: 46.1 (#72)
| Benchmark | Mercury 2.5 | Step 5 Preview |
|---|---|---|
| ProofBench | 3% | 42% |
| LMArena Math | — | 1470 |
Knowledge Not comparable
Mercury 2.5: —, Step 5 Preview: 41.2 (#112)
| Benchmark | Mercury 2.5 | Step 5 Preview |
|---|---|---|
| LMArena Expert | — | 1470 |
Multimodal Not comparable
Mercury 2.5: —, Step 5 Preview: 41.0 (#41)
| Benchmark | Mercury 2.5 | Step 5 Preview |
|---|---|---|
| LMArena Vision | — | 1267 |
Multilingual Not comparable
Mercury 2.5: —, Step 5 Preview: 53.8 (#54)
| Benchmark | Mercury 2.5 | Step 5 Preview |
|---|---|---|
| LMArena Non-English | — | 1432 |
| LMArena Chinese | — | 1519 |
| LMArena Russian | — | 1436 |
| LMArena Spanish | — | 1439 |
Instruction Following Not comparable
Mercury 2.5: —, Step 5 Preview: 76.0 (#50)
| Benchmark | Mercury 2.5 | Step 5 Preview |
|---|---|---|
| LMArena Instruction Following | — | 1444 |
Long Context Not comparable
Mercury 2.5: —, Step 5 Preview: 44.5 (#64)
| Benchmark | Mercury 2.5 | Step 5 Preview |
|---|---|---|
| LMArena Longer Query | — | 1455 |
Writing & Preference Not comparable
Mercury 2.5: —, Step 5 Preview: 62.8 (#71)
| Benchmark | Mercury 2.5 | Step 5 Preview |
|---|---|---|
| LMArena Text | — | 1442 |
| LMArena Creative Writing | — | 1410 |
| LMArena Multi-Turn | — | 1447 |
Frequently asked questions
Is Mercury 2.5 better than Step 5 Preview?
Step 5 Preview is the stronger model overall, scoring 47.9 to 33.5 on the Noometry Index. Mercury 2.5 costs 21× less per token, which makes it the better buy when Step 5 Preview's lead doesn't matter for your workload.
Which is cheaper, Mercury 2.5 or Step 5 Preview?
Mercury 2.5 is cheaper. It lists at $0.04 per million input tokens and $0.15 per million output tokens; Step 5 Preview lists at $1 and $2.70.
Is Mercury 2.5 or Step 5 Preview better for coding?
Step 5 Preview scores higher on coding benchmarks: 51.8 versus 39.5 in the Noometry coding category.
Which has the bigger context window?
Step 5 Preview does, with 1.02M tokens against 260K.
How many benchmarks do Mercury 2.5 and Step 5 Preview share?
3 benchmarks have published results for both models. Mercury 2.5 has 4 scored results on Noometry and Step 5 Preview has 18.