Leanstral 1.5
Summary
Leanstral 1.5 is an open-weight language model from Mistral AI, released on 30 Jun 2026. It accepts text and images and generates text, with a 262K-token context window and up to 128K output tokens per response. Mistral AI has deprecated this model.
An updated Lean 4 formal proof engineering model optimised for automated theorem proving and autoformalization. 119B total parameters, 6.5B active.
Last verified 17 Oct 2026. Every figure on this page links to its source.
Specifications
| Developer | Mistral AI |
|---|---|
| Release date | 30 Jun 2026 [models.dev] |
| Status | Deprecated [models.dev] |
| Weights | Open weights [models.dev] |
| Context window | 262K (262,144 tokens) [models.dev] |
| Max output | 128K tokens [models.dev] |
| Input | Text and images [models.dev] |
| Output | Text [models.dev] |
| Reasoning mode | Yes [models.dev] |
| Tool calling | Yes [models.dev] |
| Structured output | Yes [models.dev] |
Leanstral 1.5 API pricing by provider
USD per million tokens. Sorted by input price.
We do not currently track a paid API listing for this model.
Frequently asked questions
What is the context window of Leanstral 1.5?
Leanstral 1.5 has a context window of 262,144 tokens (262K) and can generate up to 128,000 tokens in a single response, according to models.dev.
Is Leanstral 1.5 open source?
Leanstral 1.5 is an open-weight model. Check the license terms before commercial use.
When was Leanstral 1.5 released?
Mistral AI released Leanstral 1.5 on 30 Jun 2026, according to models.dev.
Change history
- Added to the directory