Claude Code routine 403 host_not_allowed: allow Sume's hosts

A Claude Code routine on the Default environment uses Trusted network access, and a request from the session to a host outside the default allowlist fails with 403 and x-deny-reason: host_not_allowed. If your routine calls https://api.sume.com with curl, add api.sume.com to a Custom environment's Allowed domains, and add media.sume.com if it downloads finished files. A host named on an API credential is the other exception, since sessions can reach it whatever the network level says. The Sume connector is the third: its traffic goes through Anthropic's servers, so no allowlist change is needed for it.

Facts about the routine side come from the routines page and the cloud environments page read on 2026-10-03; Sume's hosts come from its Format API docs.

Why does the call fail?

Routines run in a cloud environment. The Default environment is Trusted, which the routines page says allows only the default allowlist of package registries, cloud provider APIs, container registries and common development domains. Anything else fails with that 403 and header.

The page also warns that a green status in the run list only means the session started and exited without an infrastructure error, so a blocked request surfaces in the transcript, not in the status indicator. Read the run when a Sume call returns nothing.

Which Sume hosts does a routine need?

It depends on how the routine talks to Sume. Hosted MCP through a connector needs nothing. A direct REST call needs the API host. Reading a result needs the media host, because Sume returns durable media.sume.com HTTPS URLs for generated files.

How do I change the network level?

• Open the routine, choose Edit, then the environment selector and its settings icon.
• Set Network access to Custom and list one domain per line, for example api.sume.com and media.sume.com. Tick the box to keep the default list so package installs still work.
• Save. The new policy applies from the next run.
• On an organization-shared environment the dialog is read-only; an Owner changes it from the Cloud environments page in admin settings.
• Choosing Full works but opens every domain; prefer the two named hosts.

How do I confirm the fix?

Have the routine run one read-only call first. A GET /v1/me with the key tells you whether the host is reachable before any paid run starts. The check below prints the status and the deny header, and it fails fast on a missing key.

import os, urllib.request, urllib.error
key = os.environ.get('SUME_API_KEY')
if not key:
    raise SystemExit('set SUME_API_KEY first')
req = urllib.request.Request('https://api.sume.com/v1/me',
    headers={'Authorization': 'Bearer ' + key})
try:
    with urllib.request.urlopen(req, timeout=15) as r:
        print(r.status)
except urllib.error.HTTPError as e:
    print(e.code, e.headers.get('x-deny-reason'))
    if e.headers.get('x-deny-reason') == 'host_not_allowed':
        print('add api.sume.com to Allowed domains')