---
title: "Mistral AI Leanstral 1.5 retirement announced: 2026-09-30 | Harbyn"
description: "Mistral AI Leanstral 1.5 retirement announced, effective Sep 30, 2026."
canonical: "https://harbyn.com/changes/mistral/2026-06-30-leanstral-1-5-retirement-announced"
last-updated: 2026-09-29
---

# Mistral AI Leanstral 1.5 retirement announced

Markdown version of <https://harbyn.com/changes/mistral/2026-06-30-leanstral-1-5-retirement-announced>.

Retirement - Mistral AI. medium severity. In effect.

Leanstral 1.5 (labs-leanstral-1-5), a Lean 4 formal proof engineering model released on June 30, 2026, will be retired on September 30, 2026.

The deadline passed on Sep 30, 2026.

## Facts

| Fact | Value |
| --- | --- |
| Vendor | [Mistral AI](https://harbyn.com/vendors/mistral.md) |
| Kind | Retirement |
| Severity | medium |
| Status | In effect |
| Announced | Jun 30, 2026 |
| Effective | Sep 30, 2026 |
| Added to Harbyn | Sep 29, 2026 |
| Lead time | 1 days of warning |
| Model IDs | `labs-leanstral-1-5` |
| Review | Reviewed by a person, extracted by a model |

## 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. 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://docs.mistral.ai/resources/changelogs> (changelog, fetched 2026-09-29 02:31 UTC, sha256 `6a19d0ae2bd34ac7d4a8d057c182974fafb9559d7ad55c713e179960ce054d99`)

## Related changes

### More from Mistral AI

- [Mistral OCR 4.0 (mistral-ocr-4-0) retires on September 30, 2026](https://harbyn.com/changes/mistral/2026-09-29-ocr-4-0-deprecated-and-scheduled-for-retirement.md) (Retirement, effective Sep 30, 2026)
- [Z.ai GLM 5.2 (zai-glm-5-2) retires on Mistral on October 31, 2026](https://harbyn.com/changes/mistral/2026-09-29-z-ai-glm-5-2-deprecated-and-scheduled-for-retirement.md) (Retirement, effective Oct 31, 2026)
- [client-ts 3.0.0, a new major version](https://harbyn.com/changes/mistral/2026-10-09-client-ts-3-0-0.md) (Breaking change, announced Oct 9, 2026)

### Changes at other vendors

- [OpenRouter: arcee-ai/trinity-large-thinking expire 2026-10-26](https://harbyn.com/changes/openrouter/2026-10-23-arcee-ai-trinity-large-thinking-expires-2026-10-26.md) (effective Oct 26, 2026)
- [Google Cloud Run and Functions: Node.js 20 runtime decommission](https://harbyn.com/changes/google-cloud/2026-10-08-node-js-20-runtime-decommission.md) (effective Oct 30, 2026)
- [Fireworks AI: DeepSeek V4 Flash 0731 retires from Serverless Training November 2](https://harbyn.com/changes/fireworks/2026-10-18-upcoming-serverless-training-deprecation-deepseek-v4-flash-0731.md) (effective Nov 2, 2026)
- [GitHub: GitHub Actions: macOS 14 runner image retired on November 2, 2026](https://harbyn.com/changes/github/2026-10-01-github-actions-macos-14-runner-image-retirement.md) (effective Nov 2, 2026)

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