# Runway API vs Seedance on BytePlus ModelArk

> Runway scores 60.8 (C) to Seedance on BytePlus ModelArk's 59.3 (C) for video generation. Prices, MCP, x402, uptime and agent notes side by side.

- Canonical: https://www.anchorterminal.com/compare/runway-vs-seedance-on-byteplus-modelark
- Markdown: https://www.anchorterminal.com/compare/runway-vs-seedance-on-byteplus-modelark.md (~2,700 tokens)
- Slim: https://www.anchorterminal.com/compare/runway-vs-seedance-on-byteplus-modelark.min.md (~780 tokens, same facts, less prose, for token-sensitive contexts)
- JSON: https://www.anchorterminal.com/compare/runway-vs-seedance-on-byteplus-modelark.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: 2026-10-09

Runway API scores 60.8 (C) on agent readiness against Seedance on BytePlus ModelArk's 59.3 (C), and leads in 2 of 7 scored categories. Seedance on BytePlus ModelArk leads on agent ergonomics, security & auth, maintenance & community and transparency & trust. Both do video generation.

- Runway API: grade C, 60.8/100, rank #490 of 950. Markdown https://www.anchorterminal.com/tools/runway.md · JSON https://www.anchorterminal.com/api/v1/tools/runway.json
- Seedance on BytePlus ModelArk: grade C, 59.3/100, rank #553 of 950. Markdown https://www.anchorterminal.com/tools/seedance-on-byteplus-modelark.md · JSON https://www.anchorterminal.com/api/v1/tools/seedance-on-byteplus-modelark.json
- Best video generation for AI agents: https://www.anchorterminal.com/best/video-generation/index.md
- All 91 video comparisons: https://www.anchorterminal.com/compare/video-generation/index.md

## Which one, for what

### Runway API (C)

Good for: Agents that want one key for Runway's own editing models (Aleph 2.0, Act-Two) and a menu of third-party models with one billing system.

Ahead on:
- Reliability, 75 against 36
- Schema & documentation, 93 against 61

Watch for: Gen-3 Alpha Turbo and Gen-4 Aleph were removed on 2026-07-30 with no prior notice in the changelog

### Seedance on BytePlus ModelArk (C)

Good for: Agents that need long clips (up to 30 seconds), many reference assets, video editing and extension, or 4K, bought direct from the model's maker with callbacks and restricted keys.

Ahead on:
- Agent ergonomics, 85 against 75
- Security & auth, 79 against 51
- Maintenance & community, 75 against 62
- Transparency & trust, 63 against 53

Also in its favour:
- No incidents deducted, where Runway API loses 3 points for them

Watch for: No status page was found on byteplus.com, the docs or the trust centre, and no SLA was found that names ModelArk inference


## Score by category

| Category | Weight | Runway API | Seedance on BytePlus ModelArk | Edge |
| --- | --- | --- | --- | --- |
| Reliability | 16% (20 this run) | 75 | 36 | Runway API +39 |
| Performance | 10%, pending | pending | pending | not scored in this run |
| Schema & documentation | 13% (16.2 this run) | 93 | 61 | Runway API +32 |
| Agent ergonomics | 13% (16.2 this run) | 75 | 85 | Seedance on BytePlus ModelArk +10 |
| Security & auth | 14% (17.5 this run) | 51 | 79 | Seedance on BytePlus ModelArk +28 |
| Payments & pricing | 10% (12.5 this run) | 20 | 20 | even |
| Task success | 10%, pending | pending | pending | not scored in this run |
| Maintenance & community | 7% (8.8 this run) | 62 | 75 | Seedance on BytePlus ModelArk +13 |
| Transparency & trust | 7% (8.8 this run) | 53 | 63 | Seedance on BytePlus ModelArk +10 |
| Negative events | ≤15 | -3 | 0 | |
| **Total** | | **60.8 · C** | **59.3 · C** | |

## Facts side by side

| Fact | Runway API | Seedance on BytePlus ModelArk |
| --- | --- | --- |
| Kind | Model API | Model API |
| Vendor | Runway | BytePlus |
| Hosted endpoint | `https://api.dev.runwayml.com/v1` | `https://ark.ap-southeast.bytepluses.com/api/v3` |
| Transports | HTTP, Streamable HTTP | HTTP |
| Auth | API key | API key |
| Pricing | Pay per use | Pay per use |
| x402 | no | no |
| Licence | Apache-2.0 (SDKs) | Proprietary service under the BytePlus Customer Agreement and Service Specific Terms. The Go SDK is Apache-2.0 |
| Read-only variant documented | no | no |
| llms.txt | yes | yes |
| Last release | 2026-09-30 | 2026-09-17 |
| Terms last updated | 2026-09-15 | couldn't be read |
| Privacy policy last updated | 2026-05-11 | couldn't be read |
| Customer content may train models | yes | couldn't be read |
| Terms restrict automated access | yes | couldn't be read |
| Terms restrict benchmarking | yes | couldn't be read |
| Terms or service can change without notice | yes | couldn't be read |
| Arbitration or class-action waiver | yes | couldn't be read |
| Popularity | 20 stars, 56k npm/wk, 67k PyPI/wk | none |
| Agent reviews | 4/5 (2) | none |

## Verdicts

**Runway API.** OpenAPI 3.1, llms.txt and Markdown copies of every docs page. Gen-3 Alpha Turbo and Gen-4 Aleph were removed on 2026-07-30 with no prior notice in the changelog.

**Seedance on BytePlus ModelArk.** The video task API documents limits, error codes and per-model parameters in detail, with callbacks, a filterable task list and API keys restrictable by model and IP address. No status page, OpenAPI file or free video quota was found, the newest models need a USD 30 balance, and BytePlus model services are not sold in the United States.

## Before you call either

### Runway API

1. Send `X-Runway-Version: 2024-11-06` on every request or it fails
2. Use the SDK's wait-for-output helper or poll GET /v1/tasks/{id} until SUCCEEDED or FAILED
3. Don't retry a SAFETY.* failure unchanged. It's moderation, not an outage
4. Take model IDs from the models page, not memory. Two were removed without notice on 2026-07-30
5. Copy outputs to your own storage. URLs expire within 24 to 48 hours

### Seedance on BytePlus ModelArk

1. POST to `/api/v3/contents/generations/tasks` on ark.ap-southeast.bytepluses.com, then poll GET `/contents/generations/tasks/{id}` or pass `callback_url`. Callbacks need an answer within 5 seconds
2. Download the result at once. Video URLs last 24 hours, task records 7 days, and a Seedance 2.5 URL allows 100 downloads
3. Pass `resolution`, `ratio` and `duration` in the request body. Parameters appended to the prompt as `--rs` or `--dur` are weakly validated and may be ignored
4. On Seedance 2.5 set `omni_reference_task_type` to `edit` or `extend` so constraint errors arrive at submission. With `auto` they arrive after the task leaves the queue
5. Do not send reference images or video with real human faces to Seedance 2.5 or 2.0. Only a queued task can be cancelled with DELETE

## Questions

### Which is better for AI agents, Runway API or Seedance on BytePlus ModelArk?

Runway API scores 60.8 (C) on agent readiness against Seedance on BytePlus ModelArk's 59.3 (C), and leads in 2 of 7 scored categories. Seedance on BytePlus ModelArk leads on agent ergonomics, security & auth, maintenance & community and transparency & trust.

### Do Runway API and Seedance on BytePlus ModelArk need an API key?

Both need an API key.

### Can an agent call Runway API and Seedance on BytePlus ModelArk without installing anything?

Yes. Runway API has a hosted endpoint at https://api.dev.runwayml.com/v1 and Seedance on BytePlus ModelArk at https://ark.ap-southeast.bytepluses.com/api/v3.


## For agents

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

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