Step 3.5 Flash 2603 vs Viv Fast vs MiMo-V2.5
MiMo-V2.5 comes out ahead, 79 to 75 and 62 on our weighted score, though Step 3.5 Flash 2603 is 14% cheaper per token.
StepFunStep 3.5 Flash 2603
62/100- ECI—
- Price$0.10 / $0.30
- Context256K
VivgridViv Fast
75/100- ECI—
- Price$0.13 / $0.40
- Context1M
- Our pick
XiaomiMiMo-V2.5
79/100- ECI—
- Price$0.14 / $0.28
- Context1.05M
MiMo-V2.5 is our pick
MiMo-V2.5 is the better all-round choice, scoring 79/100 against Viv Fast (75) and Step 3.5 Flash 2603 (62). It leads on inputs & features. Step 3.5 Flash 2603 wins on price. The score weighs price 50%, inputs & features 30%, context window 20%. None of the shared benchmarks cover every model here yet, so capability is left out of this verdict.
- CapabilityNot enough dataNo independent benchmark covers every model here yet
- Lowest priceStep 3.5 Flash 2603Step 3.5 Flash 2603 $0.15 · MiMo-V2.5 $0.175 · Viv Fast $0.198 per 1M tokens (3:1 blend)
- Longest contextMiMo-V2.5MiMo-V2.5 1,048,576 · Viv Fast 1,000,000 · Step 3.5 Flash 2603 256,000 tokens
- Widest inputsMiMo-V2.5Step 3.5 Flash 2603: Text · Viv Fast: Text, Images · MiMo-V2.5: Text, Images, Audio, Video
- Self-hostingStep 3.5 Flash 2603 and MiMo-V2.5Publishes downloadable weights
| Measure | Weight | Step 3.5 Flash 2603 | Viv Fast | MiMo-V2.5 |
|---|---|---|---|---|
| Price | 50% | 89 | 83 | 86 |
| Inputs & features | 30% | 35 | 70 | 80 |
| Context window | 20% | 36 | 60 | 61 |
| Overall | 100% | 62/100 | 75/100 | 79/100 |
Left out because at least one model lacks the data: capability. The remaining weights were rescaled.
Every spec in one table
Highlighted cells lead their row. Dashes mean the data is not published.
| Specification | Step 3.5 Flash 2603StepFun | Viv FastVivgrid | MiMo-V2.5Xiaomi |
|---|---|---|---|
| Capability | |||
| Capabilities Index (ECI) | — | — | — |
| ECI rank | — | — | — |
| Price per million tokens | |||
| Input | $0.10 (best) | $0.13 | $0.14 |
| Output | $0.30 | $0.40 | $0.28 (best) |
| Cached input | $0.02 | $0.05 | $0.0028 (best) |
| Blended (3:1) | $0.15 (best) | $0.198 | $0.175 |
| Long-context rate | Same rate | Same rate | Same rate |
| Price source | Official StepFun (Global) API | Official Vivgrid API | Official Xiaomi API |
| Limits | |||
| Context window | 256,000 tokens | 1,000,000 tokens | 1,048,576 tokens (best) |
| Max output | 256,000 tokens (best) | 256,000 tokens (best) | 131,072 tokens |
| Inputs and features | |||
| Text | Yes | Yes | Yes |
| Images | No | Yes | Yes |
| PDFs | No | No | No |
| Audio | No | No | Yes |
| Video | No | No | Yes |
| Reasoning | Yeslow · high | Yeslow · high · max | Yes |
| Tool calling | Yes | Yes | Yes |
| Structured output | No | Yes | No |
| Availability | |||
| Weights | Open | Proprietary | Open |
| API model ID | step-3.5-flash-2603 | viv-fast | mimo-v2.5 |
| API providers | 3 | 1 | 21 (best) |
| Released | Apr 2, 2026 | Sep 21, 2026 | Apr 22, 2026 |
| Knowledge cutoff | Jan 2025 | Sep 2026 | Dec 2024 |
What would a month cost?
Enter your expected volume in millions of tokens. List prices only; caching and batch discounts would lower these.
- Step 3.5 Flash 2603$1.60
- Viv Fast$2.10
- MiMo-V2.5$1.96
Which should you choose?
Which is better: Step 3.5 Flash 2603, Viv Fast or MiMo-V2.5?
MiMo-V2.5 is the better all-round choice, scoring 79/100 against Viv Fast (75) and Step 3.5 Flash 2603 (62). It leads on inputs & features. Step 3.5 Flash 2603 wins on price. The score weighs price 50%, inputs & features 30%, context window 20%. None of the shared benchmarks cover every model here yet, so capability is left out of this verdict.
Which is cheaper, Step 3.5 Flash 2603, Viv Fast or MiMo-V2.5?
Step 3.5 Flash 2603 is cheaper at $0.10 input / $0.30 output per million tokens (official StepFun (Global) API price). MiMo-V2.5 costs $0.14 input / $0.28 output per million tokens (official Xiaomi API price); Viv Fast costs $0.13 input / $0.40 output per million tokens (official Vivgrid API price). At a typical mix of three input tokens to one output token, that is $0.15 per million tokens for Step 3.5 Flash 2603 versus $0.175 for MiMo-V2.5 (1.2× as much) and $0.198 for Viv Fast (1.3× as much).
Which scores higher on benchmarks?
There is no independent benchmark that covers all three models yet. Step 3.5 Flash 2603 has not been scored yet, Viv Fast has not been scored yet and MiMo-V2.5 has not been scored yet.
Which is better for coding?
There are no published SWE-bench Verified results for Step 3.5 Flash 2603, Viv Fast and MiMo-V2.5 yet, so there is no like-for-like coding score. Test both on a sample of your own tasks. All three support tool calling for agent workflows.
Which has the bigger context window?
MiMo-V2.5 has the largest context window at 1,048,576 tokens, against 1,000,000 for Viv Fast and 256,000 for Step 3.5 Flash 2603. Maximum output per response: Step 3.5 Flash 2603 up to 256,000, Viv Fast up to 256,000, MiMo-V2.5 up to 131,072 tokens.
Which can read images, PDFs, audio or video?
Step 3.5 Flash 2603 accepts text; Viv Fast accepts text and images; MiMo-V2.5 accepts text, images, audio and video. MiMo-V2.5 handles the widest range of inputs.
Are any of these open source?
Step 3.5 Flash 2603 and MiMo-V2.5 publishes its weights and can be self-hosted; Viv Fast is proprietary.
Which is newer?
Viv Fast is the newest, released Sep 21, 2026. MiMo-V2.5 came out Apr 22, 2026; Step 3.5 Flash 2603 came out Apr 2, 2026. Knowledge cutoff: Step 3.5 Flash 2603 Jan 2025, Viv Fast Sep 2026, MiMo-V2.5 Dec 2024.
How do you decide the winner?
Each model gets a 0–100 score on capability (50%, independent benchmark results); price (25%, blended price per million tokens (3 input : 1 output), log scale); inputs & features (15%, image, PDF, audio and video input, tool calling, structured output and reasoning); context window (10%, maximum tokens per request, log scale). Dimensions missing for any model are dropped and the remaining weights rescaled, so every model is judged on the same evidence. Specs and prices come from public model listings and the labs’ own API pages; capability scores come from independent benchmark runs. Data updated Oct 4, 2026.
