---
title: "Anthropic Limited networking applies allowed_hosts to web tools: 2026-10-07 | Harbyn"
description: "Anthropic Limited networking applies allowed_hosts to web tools, announced Oct 7, 2026."
canonical: "https://harbyn.com/changes/anthropic/2026-10-07-limited-networking-applies-allowed-hosts-to-web-tools"
last-updated: 2026-10-07
---

# Anthropic Limited networking applies allowed\_hosts to web tools

Markdown version of <https://harbyn.com/changes/anthropic/2026-10-07-limited-networking-applies-allowed-hosts-to-web-tools>.

Behavior change - Anthropic. medium severity. In effect.

In Claude Managed Agents, limited-networking environments apply allowed\_hosts to web\_search and web\_fetch. Fetches to unmatched hosts return a url\_not\_allowed error result, and search omits results from those hosts. If no hosts are listed, neither tool returns pages or search results. Session creation or update also fails with a 400 error when an enabled web tool’s allowed\_domains includes an entry outside allowed\_hosts.

## Facts

| Fact | Value |
| --- | --- |
| Vendor | [Anthropic](https://harbyn.com/vendors/anthropic.md) |
| Kind | Behavior change |
| Severity | medium |
| Status | In effect |
| Announced | Oct 7, 2026 |
| Added to Harbyn | Oct 7, 2026 |
| Lead time | No dated deadline |
| Symbols | `web_search`, `web_fetch`, `allowed_hosts`, `allowed_domains` |
| Review | Automated, extracted by a model |

## Find it in your code

```sh
npx harbyn scan
```

This change names no identifier the scanner can match line by line, so the scan tells you whether your repository uses Anthropic, from its packages and API hosts. Nothing leaves your machine.

## Sources

Where this event comes from: the page we read, when we read it, and the hash of that snapshot.

- <https://platform.claude.com/docs/en/release-notes/overview.md> (changelog, fetched 2026-10-07 23:09 UTC, sha256 `087db9568b7f8e5e4dc9b879745f06bad3b0487413a58c1a02c818648ca23be2`)

## Related changes

### More from Anthropic

- [Claude Haiku 5.5 rejects manual extended thinking and returns thinking blocks by default](https://harbyn.com/changes/anthropic/2026-10-07-claude-haiku-5-5-behavior-can-break-code-written-for-claude-haiku-4-5.md) (Behavior change, announced Oct 7, 2026)
- [Claude Sonnet 4.5 model: retirement on 2026-11-30](https://harbyn.com/changes/anthropic/2026-09-30-claude-sonnet-4-5-model-retirement.md) (Retirement, effective Nov 30, 2026)
- [Claude Sonnet 5.5 rejects five Claude Sonnet 5 request patterns](https://harbyn.com/changes/anthropic/2026-09-28-claude-sonnet-5-5-changes-compatibility-with-claude-sonnet-5-code.md) (Behavior change, announced Sep 28, 2026)
- [Compliance Activity Feed no longer returns names or titles](https://harbyn.com/changes/anthropic/2026-09-24-compliance-activity-feed-no-longer-returns-names-or-titles.md) (Behavior change, announced Sep 24, 2026)

### Changes at other vendors

- [Amazon Selling Partner API: ORDER\_CHANGE notifications add PreFulfillmentStatusChange for Amazon Autos](https://harbyn.com/changes/amazon-sp-api/2026-10-14-sp-api-updates-new-listings-items-api-ivp-values-in-eu5-jp-and-ca-stores-oct-3.md) (effective Oct 28, 2026)
- [BigCommerce: 301 redirects will apply only to storefront channels](https://harbyn.com/changes/bigcommerce/2026-10-07-301-redirects-now-apply-to-storefront-channels-only.md) (effective Nov 10, 2026)
- [GitHub: Secret scanning audit log business field changes to enterprise slug](https://harbyn.com/changes/github/2026-10-20-updates-to-github-secret-scanning-7.md) (effective Nov 12, 2026)
- [Jira / Atlassian Cloud: New IP address ranges in use from January 1, 2027](https://harbyn.com/changes/atlassian-jira/2026-10-16-atlassian-cloud-adds-new-ip-address-ranges.md) (effective Jan 1, 2027)

[All upcoming deadlines](https://harbyn.com/deadlines.md)