MiMo-V2.5-Pro-UltraSpeed vs Step 3.5 Flash 2603 vs Seed 2.1 Pro
Step 3.5 Flash 2603 comes out ahead, 62 to 50 and 43 on our weighted score, and it is the cheaper option too.
XiaomiMiMo-V2.5-Pro-UltraSpeed
43/100- ECI—
- Price$1.30 / $2.61
- Context1.05M
- Our pick
StepFunStep 3.5 Flash 2603
62/100- ECI—
- Price$0.10 / $0.30
- Context256K
ByteDance SeedSeed 2.1 Pro
50/100- ECI—
- Price$0.891 / $4.45
- Context256K
Step 3.5 Flash 2603 is our pick
Step 3.5 Flash 2603 is the better all-round choice, scoring 62/100 against Seed 2.1 Pro (50) and MiMo-V2.5-Pro-UltraSpeed (43). It leads on price. MiMo-V2.5-Pro-UltraSpeed wins on context window. Seed 2.1 Pro wins on inputs & features. 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-Pro-UltraSpeed $1.63 · Seed 2.1 Pro $1.78 per 1M tokens (3:1 blend)
- Longest contextMiMo-V2.5-Pro-UltraSpeedMiMo-V2.5-Pro-UltraSpeed 1,048,576 · Step 3.5 Flash 2603 256,000 · Seed 2.1 Pro 256,000 tokens
- Widest inputsSeed 2.1 ProMiMo-V2.5-Pro-UltraSpeed: Text · Step 3.5 Flash 2603: Text · Seed 2.1 Pro: Text, Images, Video
- Self-hostingMiMo-V2.5-Pro-UltraSpeed and Step 3.5 Flash 2603Publishes downloadable weights
| Measure | Weight | MiMo-V2.5-Pro-UltraSpeed | Step 3.5 Flash 2603 | Seed 2.1 Pro |
|---|---|---|---|---|
| Price | 50% | 40 | 89 | 38 |
| Inputs & features | 30% | 35 | 35 | 80 |
| Context window | 20% | 61 | 36 | 36 |
| Overall | 100% | 43/100 | 62/100 | 50/100 |
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 | MiMo-V2.5-Pro-UltraSpeedXiaomi | Step 3.5 Flash 2603StepFun | Seed 2.1 ProByteDance Seed |
|---|---|---|---|
| Capability | |||
| Capabilities Index (ECI) | — | — | — |
| ECI rank | — | — | — |
| Price per million tokens | |||
| Input | $1.30 | $0.10 (best) | $0.891 |
| Output | $2.61 | $0.30 (best) | $4.45 |
| Cached input | $0.011 (best) | $0.02 | $0.178 |
| Blended (3:1) | $1.63 | $0.15 (best) | $1.78 |
| Long-context rate | Same rate | Same rate | Same rate |
| Price source | Official Xiaomi API | Official StepFun (Global) API | Official Volcengine Ark API |
| Limits | |||
| Context window | 1,048,576 tokens (best) | 256,000 tokens | 256,000 tokens |
| Max output | 131,072 tokens | 256,000 tokens (best) | 256,000 tokens (best) |
| Inputs and features | |||
| Text | Yes | Yes | Yes |
| Images | No | No | Yes |
| PDFs | No | No | No |
| Audio | No | No | No |
| Video | No | No | Yes |
| Reasoning | Yes | Yeslow · high | Yesminimal · low · medium · high · xhigh · max |
| Tool calling | Yes | Yes | Yes |
| Structured output | No | No | Yes |
| Availability | |||
| Weights | Open | Open | Proprietary |
| API model ID | mimo-v2.5-pro-ultraspeed | step-3.5-flash-2603 | doubao-seed-2-1-pro-260628 |
| API providers | 1 | 3 (best) | 2 |
| Released | Jun 8, 2026 | Apr 2, 2026 | Jun 23, 2026 |
| Knowledge cutoff | Dec 2024 | 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.
- MiMo-V2.5-Pro-UltraSpeed$18.27
- Step 3.5 Flash 2603$1.60
- Seed 2.1 Pro$17.81
Which should you choose?
Which is better: MiMo-V2.5-Pro-UltraSpeed, Step 3.5 Flash 2603 or Seed 2.1 Pro?
Step 3.5 Flash 2603 is the better all-round choice, scoring 62/100 against Seed 2.1 Pro (50) and MiMo-V2.5-Pro-UltraSpeed (43). It leads on price. MiMo-V2.5-Pro-UltraSpeed wins on context window. Seed 2.1 Pro wins on inputs & features. 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, MiMo-V2.5-Pro-UltraSpeed, Step 3.5 Flash 2603 or Seed 2.1 Pro?
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-Pro-UltraSpeed costs $1.30 input / $2.61 output per million tokens (official Xiaomi API price); Seed 2.1 Pro costs $0.891 input / $4.45 output per million tokens (official Volcengine Ark 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 $1.63 for MiMo-V2.5-Pro-UltraSpeed (11× as much) and $1.78 for Seed 2.1 Pro (12× as much).
Which scores higher on benchmarks?
There is no independent benchmark that covers all three models yet. MiMo-V2.5-Pro-UltraSpeed has not been scored yet, Step 3.5 Flash 2603 has not been scored yet and Seed 2.1 Pro has not been scored yet.
Which is better for coding?
There are no published SWE-bench Verified results for MiMo-V2.5-Pro-UltraSpeed, Step 3.5 Flash 2603 and Seed 2.1 Pro 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-Pro-UltraSpeed has the largest context window at 1,048,576 tokens, against 256,000 for Step 3.5 Flash 2603 and 256,000 for Seed 2.1 Pro. Maximum output per response: MiMo-V2.5-Pro-UltraSpeed up to 131,072, Step 3.5 Flash 2603 up to 256,000, Seed 2.1 Pro up to 256,000 tokens.
Which can read images, PDFs, audio or video?
MiMo-V2.5-Pro-UltraSpeed accepts text; Step 3.5 Flash 2603 accepts text; Seed 2.1 Pro accepts text, images and video. Seed 2.1 Pro handles the widest range of inputs.
Are any of these open source?
MiMo-V2.5-Pro-UltraSpeed and Step 3.5 Flash 2603 publishes its weights and can be self-hosted; Seed 2.1 Pro is proprietary.
Which is newer?
Seed 2.1 Pro is the newest, released Jun 23, 2026. MiMo-V2.5-Pro-UltraSpeed came out Jun 8, 2026; Step 3.5 Flash 2603 came out Apr 2, 2026. Knowledge cutoff: MiMo-V2.5-Pro-UltraSpeed Dec 2024, 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.
