Model comparison
Mercury 2.5 vs Step 3.5 Flash
Step 3.5 Flash is the stronger model overall, scoring 42.3 to 33.5 on the Noometry Index. Mercury 2.5 costs 2.2× less per token, which makes it the better buy when Step 3.5 Flash's lead doesn't matter for your workload.
Last verified . 0 shared benchmarks.
StepFunSummary
- The widest gap is in math, where Step 3.5 Flash leads 42.6 to 23.3.
- Mercury 2.5 is cheaper at $0.04 / $0.15 per million input/output tokens, against $0.10 / $0.30 for Step 3.5 Flash.
- Mercury 2.5 accepts more context: 260K tokens versus 256K.
- Step 3.5 Flash has downloadable open weights; the other is API-only.
Side by side
| Mercury 2.5 | Step 3.5 Flash | |
|---|---|---|
| Provider | Inception | StepFun |
| Noometry Index | 33.5 | 42.3 |
| Released | 2026-09-08 | 2026-01-29 |
| Weights | Proprietary | Open |
| Context window | 260K | 256K |
| Max output | 66K | 256K |
| Input $ / M tokens | $0.04 | $0.10 |
| Output $ / M tokens | $0.15 | $0.30 |
| Results tracked | 4 | 19 |
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Category by category
Coding Step 3.5 Flash leads
Mercury 2.5: 39.5 (#156), Step 3.5 Flash: 42.4 (#105)
| Benchmark | Mercury 2.5 | Step 3.5 Flash |
|---|---|---|
| SciCode | 38.5% | — |
| LMArena Coding | — | 1436 |
| ALE-Bench | 301.65 | — |
Reasoning Too close to call
Mercury 2.5: 22.4 (#193), Step 3.5 Flash: 22.2 (#202)
| Benchmark | Mercury 2.5 | Step 3.5 Flash |
|---|---|---|
| NYT Connections (extended) | — | 28.4% |
| CritPt | 0% | — |
| LMArena Hard Prompts | — | 1411 |
Math Step 3.5 Flash leads
Mercury 2.5: 23.3 (#272), Step 3.5 Flash: 42.6 (#84)
| Benchmark | Mercury 2.5 | Step 3.5 Flash |
|---|---|---|
| MathArena Final-Answer Competitions | — | 66.8% |
| ProofBench | 3% | — |
| LMArena Math | — | 1408 |
Knowledge Not comparable
Mercury 2.5: —, Step 3.5 Flash: 39.6 (#132)
| Benchmark | Mercury 2.5 | Step 3.5 Flash |
|---|---|---|
| LMArena Expert | — | 1421 |
Multilingual Not comparable
Mercury 2.5: —, Step 3.5 Flash: 50.5 (#119)
| Benchmark | Mercury 2.5 | Step 3.5 Flash |
|---|---|---|
| LMArena Non-English | — | 1385 |
| LMArena Chinese | — | 1447 |
| LMArena French | — | 1421 |
| LMArena German | — | 1405 |
| LMArena Japanese | — | 1354 |
| LMArena Korean | — | 1352 |
| LMArena Russian | — | 1385 |
| LMArena Spanish | — | 1419 |
Instruction Following Not comparable
Mercury 2.5: —, Step 3.5 Flash: 73.1 (#124)
| Benchmark | Mercury 2.5 | Step 3.5 Flash |
|---|---|---|
| LMArena Instruction Following | — | 1385 |
Long Context Not comparable
Mercury 2.5: —, Step 3.5 Flash: 42.8 (#117)
| Benchmark | Mercury 2.5 | Step 3.5 Flash |
|---|---|---|
| LMArena Longer Query | — | 1402 |
Writing & Preference Not comparable
Mercury 2.5: —, Step 3.5 Flash: 58.8 (#113)
| Benchmark | Mercury 2.5 | Step 3.5 Flash |
|---|---|---|
| LMArena Text | — | 1403 |
| LMArena Creative Writing | — | 1357 |
| LMArena Multi-Turn | — | 1405 |
Frequently asked questions
Is Mercury 2.5 better than Step 3.5 Flash?
Step 3.5 Flash is the stronger model overall, scoring 42.3 to 33.5 on the Noometry Index. Mercury 2.5 costs 2.2× less per token, which makes it the better buy when Step 3.5 Flash's lead doesn't matter for your workload.
Which is cheaper, Mercury 2.5 or Step 3.5 Flash?
Mercury 2.5 is cheaper. It lists at $0.04 per million input tokens and $0.15 per million output tokens; Step 3.5 Flash lists at $0.10 and $0.30.
Is Mercury 2.5 or Step 3.5 Flash better for coding?
Step 3.5 Flash scores higher on coding benchmarks: 42.4 versus 39.5 in the Noometry coding category.
Which has the bigger context window?
Mercury 2.5 does, with 260K tokens against 256K.
How many benchmarks do Mercury 2.5 and Step 3.5 Flash share?
0 benchmarks have published results for both models. Mercury 2.5 has 4 scored results on Noometry and Step 3.5 Flash has 19.