OpenAI API vs StepFun API

OpenAI API

Official OpenAPI document and an llms.txt index. Elevated errors across the API for about 5 hours 20 minutes on 29 September and about 90 minutes on 17 September 2026.

StepFun API

StepFun's API serves Step 5 Preview with a 1M-token context, video input, strict JSON Schema output and published per-token prices, documented in Markdown with an llms.txt. The model is a preview with no release date found, there's no free allowance or SLA, and the terms and privacy policy leave room to train on customer data.

OpenAI API

1. Build on the Responses API. Astra calls tools only there
2. Use gpt-6-luna for routing and extraction and gpt-6.1-sol for most work. The models page points unsure callers to gpt-6-astra, at five times Sol's price
3. Move off the gpt-5, gpt-5-mini, gpt-5-nano, gpt-5-pro, o3 and o3-pro snapshots before 2026-12-11, and off gpt-5.1, gpt-5.3-codex and gpt-5.4-nano before 2027-04-01
4. Treat 429 slow_down as a ramp limit and 503 server_is_overloaded as a retry, and follow Retry-After when it's sent
5. Prompts over 272K tokens cost double on input. Trim before you pay for it

StepFun API

1. Set max_tokens yourself. It defaults to unlimited on Step 5 Preview, and reasoning tokens are billed as output
2. Use response_format with type: json_schema and strict: true when the shape matters. JSON Mode alone isn't schema-checked
3. Back off and retry on 429, 500, 503 and 504. The docs give no Retry-After header or backoff schedule
4. Expect HTTP 451 or finish_reason: content_filter when content fails StepFun's review, and don't retry the same input
5. Use api.stepfun.ai for the international platform. api.stepfun.com is the China platform with yuan pricing