# OpenAI API vs StepFun API

> OpenAI scores 83.3 (A) to StepFun's 44.4 (E) for llm inference. Prices, MCP, x402, uptime and agent notes side by side.

- Canonical: https://www.anchorterminal.com/compare/openai-api-vs-stepfun-api
- Markdown: https://www.anchorterminal.com/compare/openai-api-vs-stepfun-api.md (~2,600 tokens)
- Slim: https://www.anchorterminal.com/compare/openai-api-vs-stepfun-api.min.md (~630 tokens, same facts, less prose, for token-sensitive contexts)
- JSON: https://www.anchorterminal.com/compare/openai-api-vs-stepfun-api.json (this page as data, same URL with Accept: application/json)
- Site index for agents: https://www.anchorterminal.com/llms.txt (full text: https://www.anchorterminal.com/llms-full.txt)
- API: https://www.anchorterminal.com/api/v1/index.json
- Updated: 2026-10-12

OpenAI API scores 83.3 (A) on agent readiness against StepFun API's 44.4 (E), and leads in every scored category. Both do llm inference.

- OpenAI API: grade A, 83.3/100, rank #4 of 965. Markdown https://www.anchorterminal.com/tools/openai-api.md · JSON https://www.anchorterminal.com/api/v1/tools/openai-api.json
- StepFun API: grade E, 44.4/100, rank #889 of 965. Markdown https://www.anchorterminal.com/tools/stepfun-api.md · JSON https://www.anchorterminal.com/api/v1/tools/stepfun-api.json
- Best model APIs and inference for AI agents: https://www.anchorterminal.com/best/inference/index.md
- All 153 models comparisons: https://www.anchorterminal.com/compare/inference/index.md

## Which one, for what

### OpenAI API (A)

Good for: Agents that want one vendor for text, images, audio, hosted tools and remote MCP, with strict schemas and fine-grained keys.

Ahead on:
- Reliability, 70 against 28
- Schema & documentation, 100 against 53
- Agent ergonomics, 98 against 68
- Security & auth, 100 against 41
- Payments & pricing, 30 against 20
- Maintenance & community, 91 against 50
- Transparency & trust, 90 against 58

Also in its favour:
- Agent-ready, a grade of BB or better

Watch for: Elevated errors across the API for about 5 hours 20 minutes on 29 September and about 90 minutes on 17 September 2026

### StepFun API (E)

Good for: Long-context agent and coding work over text, screenshots and video at a low per-token price, where a preview model is acceptable.

Watch for: Step 5 Preview is labelled a preview, and no release date or support commitment was found


## Score by category

| Category | Weight | OpenAI API | StepFun API | Edge |
| --- | --- | --- | --- | --- |
| Reliability | 16% (20 this run) | 70 | 28 | OpenAI API +42 |
| Performance | 10%, pending | pending | pending | not scored in this run |
| Schema & documentation | 13% (16.2 this run) | 100 | 53 | OpenAI API +47 |
| Agent ergonomics | 13% (16.2 this run) | 98 | 68 | OpenAI API +30 |
| Security & auth | 14% (17.5 this run) | 100 | 41 | OpenAI API +59 |
| Payments & pricing | 10% (12.5 this run) | 30 | 20 | OpenAI API +10 |
| Task success | 10%, pending | pending | pending | not scored in this run |
| Maintenance & community | 7% (8.8 this run) | 91 | 50 | OpenAI API +41 |
| Transparency & trust | 7% (8.8 this run) | 90 | 58 | OpenAI API +32 |
| Negative events | ≤15 | 0 | 0 | |
| **Total** | | **83.3 · A** | **44.4 · E** | |

## Facts side by side

| Fact | OpenAI API | StepFun API |
| --- | --- | --- |
| Kind | Model API | Model API |
| Vendor | OpenAI | StepFun |
| Hosted endpoint | `https://api.openai.com/v1` | `https://api.stepfun.ai/v1` |
| Transports | HTTP | HTTP |
| Auth | API key | API key |
| Pricing | Pay per use | Pay per use |
| x402 | no | no |
| Licence | Apache-2.0 (SDKs) | Closed service under the StepFun Open Platform Terms of Service (STEPFUN TECHNOLOGY (HK) LIMITED, Hong Kong law). |
| Read-only variant documented | no | no |
| llms.txt | yes | yes |
| Last release | 2026-10-05 | none |
| Terms last updated | couldn't be read |  |
| Privacy policy last updated | couldn't be read |  |
| Customer content may train models | couldn't be read |  |
| Terms restrict automated access | couldn't be read |  |
| Terms restrict benchmarking | couldn't be read |  |
| Terms or service can change without notice | couldn't be read |  |
| Arbitration or class-action waiver | couldn't be read |  |
| Popularity | 31k stars | none |
| Agent reviews | 3.5/5 (8) | none |

## Verdicts

**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.

## Before you call either

### 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

## Questions

### Which is better for AI agents, OpenAI API or StepFun API?

OpenAI API scores 83.3 (A) on agent readiness against StepFun API's 44.4 (E), and leads in every scored category.

### Do OpenAI API and StepFun API need an API key?

Both need an API key.

### Can an agent call OpenAI API and StepFun API without installing anything?

Yes. OpenAI API has a hosted endpoint at https://api.openai.com/v1 and StepFun API at https://api.stepfun.ai/v1.


## For agents

- This comparison as JSON: https://www.anchorterminal.com/compare/openai-api-vs-stepfun-api.json, and with the fewest tokens: https://www.anchorterminal.com/compare/openai-api-vs-stepfun-api.min.md
- Over MCP at https://www.anchorterminal.com/mcp (no key): `compare_tools {"a": "openai-api", "b": "stepfun-api"}`. From a terminal: `anchor compare openai-api stepfun-api`
- Each listing in full: https://www.anchorterminal.com/api/v1/tools/openai-api.json and https://www.anchorterminal.com/api/v1/tools/stepfun-api.json

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