HappyHorse 1.1 on Cloudflare: 2,500-character prompt limit

Cloudflare's HappyHorse 1.1 T2V page limits the prompt to 2,500 characters. It takes 3 to 15 second clips at 720P or 1080P. HappyHorse is not a model in the Sume video catalog, so there is no Sume prompt limit to compare it to.

What the Cloudflare page lists

Why the limit matters

Prompts written for models with long structured briefs can pass 2,500 characters once you add shot lists, camera moves and dialogue. If your prompt generator can reach that length, truncate or split by shot before sending, and send one shot per request. 2,500 characters is roughly 400 words.

Note on conflicting resolutions

Alibaba's own model list describes happyhorse-1.1 text-to-video at 480P, 720P and 1080P. Cloudflare lists 720P and 1080P only. Treat the host you call as the authority for what is accepted.

On Sume

Sume's video catalog has Seedance, Wan 3.0, Kling 3, MiniMax H3, Gemini Omni Flash 1.1 and Grok Imagine; I found no HappyHorse id. Read GET /v1/videos/models for the live list before planning around any model.

Writing inside the cap

A good video prompt is rarely over 1,000 characters. When one is, it is usually because several shots are packed into one request. The better fix is one request per shot, with the same character and setting description repeated in each. Keep a short style paragraph, then one paragraph for action, one for camera and one for audio, and measure the length in code before the call.

A simple guard is to count characters in your template and fail the job locally when it passes 2,500, rather than paying for a request the host will reject. The same guard is cheap to keep when you later switch models, since each model has its own limit and Sume's GET /v1/videos/models is where you read the supported fields for the Sume ids.