Viv Fast vs Step 3.5 Flash 2603
Viv Fast comes out ahead, 75 to 62 on our weighted score, though Step 3.5 Flash 2603 is 24% cheaper per token.
- Our pick
VivgridViv Fast
75/100- ECI—
- Price$0.13 / $0.40
- Context1M
StepFunStep 3.5 Flash 2603
62/100- ECI—
- Price$0.10 / $0.30
- Context256K
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Make it a three-way comparison.
Viv Fast is our pick
Viv Fast is the better all-round choice, scoring 75/100 against Step 3.5 Flash 2603 (62). It leads on inputs & features and context window. 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 · Viv Fast $0.198 per 1M tokens (3:1 blend)
- Longest contextViv FastViv Fast 1,000,000 · Step 3.5 Flash 2603 256,000 tokens
- Widest inputsViv FastViv Fast: Text, Images · Step 3.5 Flash 2603: Text
- Self-hostingStep 3.5 Flash 2603Publishes downloadable weights
| Measure | Weight | Viv Fast | Step 3.5 Flash 2603 |
|---|---|---|---|
| Price | 50% | 83 | 89 |
| Inputs & features | 30% | 70 | 35 |
| Context window | 20% | 60 | 36 |
| Overall | 100% | 75/100 | 62/100 |
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 | Viv FastVivgrid | Step 3.5 Flash 2603StepFun |
|---|---|---|
| Capability | ||
| Capabilities Index (ECI) | — | — |
| ECI rank | — | — |
| Price per million tokens | ||
| Input | $0.13 | $0.10 (best) |
| Output | $0.40 | $0.30 (best) |
| Cached input | $0.05 | $0.02 (best) |
| Blended (3:1) | $0.198 | $0.15 (best) |
| Long-context rate | Same rate | Same rate |
| Price source | Official Vivgrid API | Official StepFun (Global) API |
| Limits | ||
| Context window | 1,000,000 tokens (best) | 256,000 tokens |
| Max output | 256,000 tokens | 256,000 tokens |
| Inputs and features | ||
| Text | Yes | Yes |
| Images | Yes | No |
| PDFs | No | No |
| Audio | No | No |
| Video | No | No |
| Reasoning | Yeslow · high · max | Yeslow · high |
| Tool calling | Yes | Yes |
| Structured output | Yes | No |
| Availability | ||
| Weights | Proprietary | Open |
| API model ID | viv-fast | step-3.5-flash-2603 |
| API providers | 1 | 3 (best) |
| Released | Sep 21, 2026 | Apr 2, 2026 |
| Knowledge cutoff | Sep 2026 | Jan 2025 |
What would a month cost?
Enter your expected volume in millions of tokens. List prices only; caching and batch discounts would lower these.
- Viv Fast$2.10
- Step 3.5 Flash 2603$1.60
Which should you choose?
Which is better: Viv Fast or Step 3.5 Flash 2603?
Viv Fast is the better all-round choice, scoring 75/100 against Step 3.5 Flash 2603 (62). It leads on inputs & features and context window. 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, Viv Fast or Step 3.5 Flash 2603?
Step 3.5 Flash 2603 is cheaper at $0.10 input / $0.30 output per million tokens (official StepFun (Global) 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 $0.198 for Viv Fast (1.3× as much).
Which scores higher on benchmarks?
There is no independent benchmark that covers both models yet. Viv Fast has not been scored yet and Step 3.5 Flash 2603 has not been scored yet.
Which is better for coding?
There are no published SWE-bench Verified results for Viv Fast and Step 3.5 Flash 2603 yet, so there is no like-for-like coding score. Test both on a sample of your own tasks. Both support tool calling for agent workflows.
Which has the bigger context window?
Viv Fast has the largest context window at 1,000,000 tokens, against 256,000 for Step 3.5 Flash 2603. Maximum output per response: Viv Fast up to 256,000, Step 3.5 Flash 2603 up to 256,000 tokens.
Which can read images, PDFs, audio or video?
Viv Fast accepts text and images; Step 3.5 Flash 2603 accepts text. Viv Fast handles the widest range of inputs.
Are any of these open source?
Step 3.5 Flash 2603 publishes its weights and can be self-hosted; Viv Fast is proprietary.
Which is newer?
Viv Fast is the newest, released Sep 21, 2026. Step 3.5 Flash 2603 came out Apr 2, 2026. Knowledge cutoff: Viv Fast Sep 2026, Step 3.5 Flash 2603 Jan 2025.
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.
