StepFun Step 3.5 Flash vs Runway Gen-3
Which one should you pick? Here's the full breakdown.
StepFun Step 3.5 Flash
StepFun's (China) agent-focused open-weight model -- Step 3.5 Flash launched 2026-02-01. 196B sparse MoE, ~11B active. Benchmarks slightly ahead of DeepSeek V3.2 at over 3x smaller total size. Step 3 (321B / 38B active, Apache 2.0) and Step3-VL-10B multimodal also in the family
Runway Gen-3
The most capable AI video generator available -- text-to-video that actually looks professional
| Category | StepFun Step 3.5 Flash | Runway Gen-3 |
|---|---|---|
| Ease of Use | 6.0 | 7.0 |
| Output Quality | 8.0 | 9.0 |
| Value | 9.0 | 6.0 |
| Features | 8.0 | 9.0 |
| Overall | 7.8 | 7.8 |
Pricing Comparison
| Feature | StepFun Step 3.5 Flash | Runway Gen-3 |
|---|---|---|
| Free Tier | Yes | Yes |
| Starting Price | $0 | $0 |
Which Should You Pick?
Pick StepFun Step 3.5 Flash if...
- ✓Better value for money (9/10)
Teams building agent systems on Chinese open-weight foundations who want something other than DeepSeek or Qwen, especially if agentic tool-use is the primary workload. Also good for Chinese-market products where StepFun's domestic tuning advantages matter. And for anyone looking to add diversity to their open-weight evaluation matrix beyond the top-3 Chinese labs.
Visit StepFun Step 3.5 FlashPick Runway Gen-3 if...
- ✓Higher output quality (9 vs 8)
- ✓Easier to use (7 vs 6)
- ✓More features (9 vs 8)
Video creators, filmmakers, and agencies who need the best possible AI video quality and have budget for credits. The creative suite tools (inpainting, motion brush) are best-in-class.
Visit Runway Gen-3Our Verdict
StepFun Step 3.5 Flash and Runway Gen-3 are extremely close overall. Your choice comes down to specific needs -- StepFun Step 3.5 Flash is better for teams building agent systems on chinese open-weight foundations who want something other than deepseek or qwen, especially if agentic tool-use is the primary workload, while Runway Gen-3 works best for video creators, filmmakers, and agencies who need the best possible ai video quality and have budget for credits.