Is there a Runway Agent API? What the help pages say, and Sume's

The Runway help pages I read describe Agent as an in-app chat experience and describe two programmable routes next to it: publishing a Workflow as an Endpoint, and connecting an MCP client. They do not describe an endpoint that sends Agent a prompt, so I would not assume one exists. Sume does ship that shape: POST /v1/agent/completions with model sume-agent.

What each page offers

Sume's agent call

messages may hold system and user turns only, or you may send a single instruction. Attachments are images only today; other file types follow later. The response is a run: poll /v1/agent-runs for the result. There is no streaming and no thread continuation.

import json, os, urllib.request, uuid

body = {"model": "sume-agent",
        "instruction": "Write a 3-line caption for a trail mug ad.",
        "generation_spend_cap_usd": 2}
req = urllib.request.Request(
    "https://api.sume.com/v1/agent/completions",
    data=json.dumps(body).encode(), method="POST",
    headers={"Authorization": "Bearer " + os.environ["SUME_API_KEY"],
             "Content-Type": "application/json",
             "Idempotency-Key": str(uuid.uuid4())})
with urllib.request.urlopen(req) as resp:
    print(json.load(resp))

How to decide

• Need a reusable, repeatable pipeline: a Format, on either platform.
• Need one open-ended request from code: Sume's Agent Completions.
• Need the vendor's chat inside your client: the MCP on each side.

Limits of this comparison

I read Runway's help pages, not its developer reference, so a feature that exists only there would not show up here. Check the Developer Portal for the current list before you build, and treat Sume's side as what its docs list today.