StepFun Step 3.5 Flash vs Grok Speech (STT + TTS APIs)
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
Grok Speech (STT + TTS APIs)
xAI's standalone voice APIs -- launched 2026-04-17. Built on the stack that powers Grok Voice, Tesla vehicles, and Starlink customer support. $0.10/hr STT batch, $4.20 per 1M characters TTS, 25+ languages, word-level timestamps + speaker diarization
| Category | StepFun Step 3.5 Flash | Grok Speech (STT + TTS APIs) |
|---|---|---|
| Ease of Use | 6.0 | 7.0 |
| Output Quality | 8.0 | 8.5 |
| Value | 9.0 | 9.0 |
| Features | 8.0 | 8.0 |
| Overall | 7.8 | 8.1 |
Pricing Comparison
| Feature | StepFun Step 3.5 Flash | Grok Speech (STT + TTS APIs) |
|---|---|---|
| Free Tier | Yes | No |
| Starting Price | $0 | $0.10 |
Which Should You Pick?
Pick StepFun Step 3.5 Flash if...
- ✓Has a free tier
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 Grok Speech (STT + TTS APIs) if...
- ✓Easier to use (7 vs 6)
Developers building voice agents, real-time transcription tools, accessibility features, or high-volume TTS workloads where the cost per hour of audio actually matters at scale. Strong fit for phone-call and meeting transcription use cases where xAI's published WER advantage (5.0% on phone-call entities vs. ElevenLabs 12.0%) compounds quickly.
Visit Grok Speech (STT + TTS APIs)Our Verdict
StepFun Step 3.5 Flash and Grok Speech (STT + TTS APIs) 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 Grok Speech (STT + TTS APIs) works best for developers building voice agents, real-time transcription tools, accessibility features, or high-volume tts workloads where the cost per hour of audio actually matters at scale.