---
title: "Anthropic claude-mythos-preview is deprecated: 2026-06-09 | Harbyn"
description: "Anthropic claude-mythos-preview is deprecated, announced Jun 9, 2026; replacement: claude-mythos-5."
canonical: "https://harbyn.com/changes/anthropic/2026-06-09-claude-mythos-preview-deprecated"
last-updated: 2026-09-21
---

# Anthropic claude-mythos-preview is deprecated

Markdown version of <https://harbyn.com/changes/anthropic/2026-06-09-claude-mythos-preview-deprecated>.

Deprecation - Anthropic. medium severity. Announced.

Anthropic lists claude-mythos-preview as deprecated since 2026-06-09 with a retirement date to be announced. Recommended replacement: claude-mythos-5.

## Facts

| Fact | Value |
| --- | --- |
| Vendor | [Anthropic](https://harbyn.com/vendors/anthropic.md) |
| Product | models |
| Kind | Deprecation |
| Severity | medium |
| Status | Announced |
| Announced | Jun 9, 2026 |
| Added to Harbyn | Sep 21, 2026 |
| Lead time | No dated deadline |
| Model IDs | `claude-mythos-preview` |
| Replacement | `claude-mythos-5` |
| Review | Automated, extracted by a deterministic parser |

## Find it in your code

```sh
npx harbyn scan
```

The scanner reads your repository on your machine and reports every file and line that uses the identifiers above, with the replacement. 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/about-claude/model-deprecations.md> (deprecations, fetched 2026-09-21 03:10 UTC, sha256 `3a2df47b1dd8818789c13f72c5e81c2cd58b539087ee855d52e9e47527075a07`)

## Related changes

### More from Anthropic

- [Claude Opus 4.1 model: retirement on 2026-08-05](https://harbyn.com/changes/anthropic/2026-06-05-claude-opus-4-1-model-retirement.md) (Retirement, effective Aug 5, 2026)
- [Claude Sonnet 4 and Claude Opus 4 models: retirement on 2026-06-15](https://harbyn.com/changes/anthropic/2026-04-14-claude-sonnet-4-and-claude-opus-4-models-retirement.md) (Retirement, effective Jun 15, 2026)
- [SDK beta headers removal for files and skills](https://harbyn.com/changes/anthropic/2026-08-27-sdk-beta-headers-removal-for-files-and-skills.md) (Deprecation, announced Aug 27, 2026)
- [Claude Enterprise Admin, Analytics and Compliance API requests should send the anthropic-version header](https://harbyn.com/changes/anthropic/2026-09-01-enterprise-admin-and-compliance-api-requests-must-send-api-version-header.md) (Behavior change, announced Sep 1, 2026)

### Changes at other vendors

- [AWS Lambda: Python 3.10 runtime deprecation](https://harbyn.com/changes/aws-lambda/2026-10-08-python-3-10-runtime-deprecation.md) (effective Oct 31, 2026)
- [Jira / Atlassian Cloud: Atlassian Analytics dashboard subscriptions being removed](https://harbyn.com/changes/atlassian-jira/2026-08-10-atlassian-analytics-dashboard-subscriptions-being-removed.md) (effective Nov 2, 2026)
- [Google Cloud Run and Functions: .NET 8 runtime deprecation](https://harbyn.com/changes/google-cloud/2026-10-08-net-8-runtime-deprecation.md) (effective Nov 10, 2026)
- [GitHub: X-GitHub-Stateless-S2S-Token header ignored from 2026-11-30](https://harbyn.com/changes/github/2026-10-02-x-github-stateless-s2s-token-header-ignored-from-2026-11-30.md) (effective Nov 30, 2026)

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