Why Did My Video Generation API Suddenly Stop Working? The Key Pool Problem Explained
·4 min read
The Problem: Price Looks Fine, But Requests Keep Failing
After testing several Chinese AI API relay stations, I found a problem more important than price: key pool exhaustion.
The symptoms are classic: the pricing page looks normal, your balance is sufficient, but video generation requests fail immediately — not rate-limited, not throttled, just outright rejected. Try again an hour later, and it works fine.
What Is a Key Pool?
The business model behind Chinese AI API relay stations works like this: the platform bulk-purchases upstream API quota (Sora 2, Kling, VEO call credits), then distributes usage to end users. This shared quota pool is the "key pool."
When the pool has quota available, requests are forwarded normally. When it's exhausted, new requests return errors immediately. This status is almost never shown on the pricing page — you see the unit price, never the current available balance.
Why Video APIs Are the Most Vulnerable
Video generation costs dramatically more per call than image generation:
| Type | Typical unit price | Requests the same quota supports |
|---|---|---|
| Image generation | $0.02–$0.14 / image | Hundreds to thousands |
| Video generation | $0.10–$0.80 / clip | Dozens |
The same key pool balance exhausts in dozens of video requests while image APIs handle hundreds. During peak hours, concurrent users accelerate depletion further. This is a structural issue in shared key pool economics, not a platform quality problem.
Practical Recommendations by Use Case
Video Generation
- Testing / low-frequency use: Relay stations are fine. The price advantage is real, occasional failures are acceptable — just retry.
- Production / high-frequency use: Connect directly to official APIs (fal.ai for Sora 2, Runway official, Kling official). You control your own quota.
Image Generation
- Relay station stability is more acceptable here. The price advantage is also greater, suitable for high-volume batch usage.
- Still recommend platforms with reasonable scale and active updates to avoid pools that never get refilled.
Questions to Ask Before Buying Relay Station Credits
- Does the platform have a pool quota alert or status page?
- Is there any availability guarantee (SLA) for video generation?
- Do purchased credits expire?
- How fast does support respond when API calls fail?
Transparency varies widely. ComputeUnion's relay station comparison covers basic platform info, but availability must be verified through your own testing.
The Bottom Line
Key pool exhaustion is a structural problem with Chinese AI API relay stations, particularly acute for video generation. For production environments with stability requirements, direct access to official API quota is the real value — not the unit price.
Author: yego | Data source: ComputeUnion's daily automated crawling across 70+ platforms
Frequently Asked Questions
Is key pool exhaustion the relay station's fault?
It's a structural issue with the shared key pool business model, not necessarily a sign of poor platform quality. The platform may be fine — but everyone shares the same upstream quota.
How do I know if a relay station's key pool is exhausted?
Most platforms don't expose real-time quota. The only reliable signal is a failed API call. Some platforms have status pages or Telegram channels that announce quota refills — check those before committing to a platform.
Do image generation APIs have the same problem?
Yes, but much less frequently. Image generation costs $0.02–$0.14 per image vs $0.10–$0.80 per video clip, so the same quota pool handles far more image requests before exhausting.
Which CN relay station is most reliable for video generation?
It depends on which upstream model you need. For production use, going directly to the official API provider (fal.ai for Sora 2, Runway, Kling) gives you your own quota that isn't shared with other users.