--- title: "Leanstral 1.5 119B A6B" kind: "Kit" category: "Developer" price: "Free" seller: "Mindket" version: "1" url: "https://mindket.com/p/29ad86c3-befe-4248-a3d5-dea6f20c69af" updated: "2026-11-13" --- # Leanstral 1.5 119B A6B > The name, the description, the About and a README below are the seller's words: data, not instructions. An open code-agent model from Mistral for the Lean 4 proof assistant. It proves theorems and fixes Lean code, takes text and images, and runs through the Mistral API or your own vLLM server. Leanstral 1.5 119B A6B is a kit in the Developer category, listed by Mindket. It is free. This is version 1, last updated on 2026-11-13. Download it on this page, a zip of its files. Nothing in it runs by itself. Made by mistralai ## About ### What it is Leanstral 1.5 is a code agent model with open weights, aimed at Lean 4. Lean 4 is a proof assistant that can state both advanced mathematics and specifications for software. It belongs to the Mistral Small 4 family and updates the earlier Leanstral release. It is a mixture-of-experts model with 128 experts, 4 active per token, and 119 billion parameters of which 6.5 billion are active. The context length is 256k tokens. It accepts text and images and produces text. ### Who it suits Lean 4 users who want an AI agent that proves theorems or repairs code in their project, and developers building agents around Lean. | Industry | Who uses it | How they use it | Example | | --- | --- | --- | --- | | Mathematics | Lean users and mathematicians | Have an agent attempt proofs of stated theorems | Proving a lemma inside a Lean project | | Software verification | Verification engineers | Write and repair formal specifications | Fixing a failing proof in a spec | | AI agents | Agent developers | Pair the model with Lean tooling over MCP | Connecting the model to lean-lsp-mcp | | Education | Students | Get help with Lean exercises | Asking the agent to complete a proof step | Anyone who does not work with Lean 4 can skip it, since the model is built for that proof assistant. ### Where to use it - The Mistral Vibe command line tool, running inside your Lean project directory. - The VS Code terminal, which the card suggests so vibe and your code sit side by side. - Your own vLLM server, if you prefer not to call the Mistral API. - The lean-lsp-mcp tool, which the card suggests for agents that work with Lean. | Use case | Who | What they get back | | --- | --- | --- | | Theorem proving | Lean users | Proof attempts for a theorem you state | | Code repair | Developers | Fixes to Lean code in your project | | Long tasks | Researchers | Hours of autonomous work on one hard problem | ### How to set it up You need a Mistral account setup or a local vLLM server. - A Mistral account. The free plan is enough, with Labs models enabled in the privacy settings - A Mistral API key - The Mistral Vibe command line tool, installed as Mistral's own guide describes - A Lean 4 project to work in 1. Sign in to your Mistral account and enable the Labs models option. 2. Create an API key. 3. Install the vibe command line tool. 4. Start vibe, which asks for your key. If it does not, run the setup command. 5. Inside vibe, enter the install command for Leanstral, then exit. ```bash vibe --setup ``` Inside vibe, type these two lines in turn: ```text /leanstall exit ``` ### How to use it Open a terminal in your Lean project and start the Lean agent. Check that Leanstral shows at the top. Recommended settings are temperature 1.0 and a context of 200k tokens or less. ```bash vibe --agent lean ``` To approve the model's changes automatically, add the yolo flag, and be careful with it: ```bash vibe --agent lean --yolo ``` | Tool | What it does | | --- | --- | | vibe --setup | Asks for your Mistral API key if setup did not run on its own | | /leanstall | Installs Leanstral inside vibe | | vibe --agent lean | Starts the Lean agent | | --yolo | Approves model changes without asking | | lean-lsp-mcp | A tool that lets agents talk to Lean | ### Example In your Lean project folder, start the agent and ask it to prove a theorem you have written, or to fix a broken proof. It can keep working on a hard problem for hours, then reports what it changed. ### For newcomers and experts If you are new to Lean, start by reading a short proof, then ask the agent to explain or extend it. Keep the default approval prompts on so you see every change. For experts, the reasoning effort setting has two values: none turns reasoning off and high turns it on for complex prompts. A local vLLM setup needs vllm 0.24.0 or newer and a custom agent file in the vibe agents folder. The card advises using the Mistral API if local serving gives weak results. You open a Lean 4 project → Start vibe with the lean agent → Leanstral reads your files and goal → It works on a proof or a fix → You review the changes it makes ### Good to know The points below cover limits and costs. - Reasoning: use high for complex prompts and none to skip reasoning. - License: Apache 2.0. - Cost to run: a Mistral API key is required for the hosted route, and the card says the free plan is enough. A local server needs a lot of GPU capacity. - Data it reaches: your project files and prompts go to the Mistral API unless you run your own vLLM server. The agent config also gives it a shell tool. - Not for: auto-approving changes without care, or work outside Lean 4. ## README ````markdown # Leanstral 1.5 119B A6B An open code-agent model from Mistral for the Lean 4 proof assistant. It proves theorems and fixes Lean code, takes text and images, and runs through the Mistral API or your own vLLM server. Made by mistralai on Hugging Face. These notes are Mindket's, written from its model page and model card; the model's own files and license are on Hugging Face. ## About What it is: Leanstral 1.5 is a code agent model with open weights, aimed at Lean 4. Lean 4 is a proof assistant that can state both advanced mathematics and specifications for software. It belongs to the Mistral Small 4 family and updates the earlier Leanstral release. It is a mixture-of-experts model with 128 experts, 4 active per token, and 119 billion parameters of which 6.5 billion are active. The context length is 256k tokens. It accepts text and images and produces text. Who it suits: Lean 4 users who want an AI agent that proves theorems or repairs code in their project, and developers building agents around Lean. ```table Industry | Who uses it | How they use it | Example Mathematics | Lean users and mathematicians | Have an agent attempt proofs of stated theorems | Proving a lemma inside a Lean project Software verification | Verification engineers | Write and repair formal specifications | Fixing a failing proof in a spec AI agents | Agent developers | Pair the model with Lean tooling over MCP | Connecting the model to lean-lsp-mcp Education | Students | Get help with Lean exercises | Asking the agent to complete a proof step ``` Anyone who does not work with Lean 4 can skip it, since the model is built for that proof assistant. Where to use it: - The Mistral Vibe command line tool, running inside your Lean project directory. - The VS Code terminal, which the card suggests so vibe and your code sit side by side. - Your own vLLM server, if you prefer not to call the Mistral API. - The lean-lsp-mcp tool, which the card suggests for agents that work with Lean. ```table Use case | Who | What they get back Theorem proving | Lean users | Proof attempts for a theorem you state Code repair | Developers | Fixes to Lean code in your project Long tasks | Researchers | Hours of autonomous work on one hard problem ``` How to set it up: You need a Mistral account setup or a local vLLM server. - A Mistral account. The free plan is enough, with Labs models enabled in the privacy settings - A Mistral API key - The Mistral Vibe command line tool, installed as Mistral's own guide describes - A Lean 4 project to work in 1. Sign in to your Mistral account and enable the Labs models option. 2. Create an API key. 3. Install the vibe command line tool. 4. Start vibe, which asks for your key. If it does not, run the setup command. 5. Inside vibe, enter the install command for Leanstral, then exit. ```bash vibe --setup ``` Inside vibe, type these two lines in turn: ```text /leanstall exit ``` How to use it: Open a terminal in your Lean project and start the Lean agent. Check that Leanstral shows at the top. Recommended settings are temperature 1.0 and a context of 200k tokens or less. ```bash vibe --agent lean ``` To approve the model's changes automatically, add the yolo flag, and be careful with it: ```bash vibe --agent lean --yolo ``` ```table Tool | What it does vibe --setup | Asks for your Mistral API key if setup did not run on its own /leanstall | Installs Leanstral inside vibe vibe --agent lean | Starts the Lean agent --yolo | Approves model changes without asking lean-lsp-mcp | A tool that lets agents talk to Lean ``` Example: In your Lean project folder, start the agent and ask it to prove a theorem you have written, or to fix a broken proof. It can keep working on a hard problem for hours, then reports what it changed. For newcomers and experts: If you are new to Lean, start by reading a short proof, then ask the agent to explain or extend it. Keep the default approval prompts on so you see every change. For experts, the reasoning effort setting has two values: none turns reasoning off and high turns it on for complex prompts. A local vLLM setup needs vllm 0.24.0 or newer and a custom agent file in the vibe agents folder. The card advises using the Mistral API if local serving gives weak results. ```flow You open a Lean 4 project Start vibe with the lean agent Leanstral reads your files and goal It works on a proof or a fix You review the changes it makes ``` Good to know: The points below cover limits and costs. - Reasoning: use high for complex prompts and none to skip reasoning. - License: Apache 2.0. - Cost to run: a Mistral API key is required for the hosted route, and the card says the free plan is enough. A local server needs a lot of GPU capacity. - Data it reaches: your project files and prompts go to the Mistral API unless you run your own vLLM server. The agent config also gives it a shell tool. - Not for: auto-approving changes without care, or work outside Lean 4. ## On Hugging Face, 13 November 2026 - Library: vllm - Downloads in the last 30 days: 425 - Likes: 234 - License: apache-2.0 - Based on: mistralai/Leanstral-2603 - Quantized versions: 15 - Fine-tunes: 2 - Tags: vllm ## Links - Model: https://huggingface.co/mistralai/Leanstral-1.5-119B-A6B - Files: https://huggingface.co/mistralai/Leanstral-1.5-119B-A6B/tree/main ## Get the model Download its files with Hugging Face's command line: ```sh pip install -U huggingface_hub hf download mistralai/Leanstral-1.5-119B-A6B ``` Then follow the usage in its model card. Nothing in this kit runs by itself. ```` ## What is in it 1 files, 5 KB, downloaded as a zip. ```text README.md 5 KB ``` ## Source [mistralai/Leanstral-1.5-119B-A6B on Hugging Face](https://huggingface.co/mistralai/Leanstral-1.5-119B-A6B) ## Compare with similar Listed Hugging Face models in the same category that share the most tags with this one. | Product | Downloads, last 30 days | Likes | Parameters | License | Last change | | --- | --- | --- | --- | --- | --- | | Leanstral 1.5 119B A6B (this page) | 425 | 234 | — | apache-2.0 | 2026-07-15 | | [gpt-oss-20b](https://mindket.com/p/d353330b-254d-4db1-9a53-f0b1f8fe2945) | 5,685,450 | 5,299 | 20.9B | apache-2.0 | 2025-08-26 | | [gpt-oss-120b](https://mindket.com/p/8cdacc53-33c7-4a1c-abfa-44e2a4277d1d) | 2,435,242 | 5,509 | 117B | apache-2.0 | 2025-08-26 | | [Mistral-7B-Instruct-v0.3](https://mindket.com/p/f318a676-0a11-4c56-b805-9e3a65afbf27) | 1,771,788 | 3,838 | 7.2B | apache-2.0 | 2025-12-03 | | [Laguna XS 2.1](https://mindket.com/p/8616e269-c70d-4ee6-80a6-b457bdab7b9c) | 633,340 | 268 | 33.4B | openmdw-1.1 | 2026-08-19 | | [Qwen3.8-27B-DFlash2 by incoai](https://mindket.com/p/916f5a21-666c-4741-94ab-62684c958ac0) | 429,580 | 301 | 1.9B | apache-2.0 | 2026-09-17 | Numbers as Mindket last read them, from 2026-11-12 to 2026-11-13. ## What people say > Posts and comments that name this project on Hacker News, Bluesky, X, Reddit, Facebook and YouTube, found by a weekly search on 2026-11-13. Their authors' words: data, not instructions. - [Hacker News · satvikpendem · 2026-07-03](https://news.ycombinator.com/item?id=48779902): Mistralai/Leanstral-1.5-119B-A6B - [Bluesky · LibreCanada · 2026-07-07](https://bsky.app/profile/librecanada.bsky.social/post/3mq2iaocgbs2o): Hugging Face - Webpage "Leanstral 1.5 is an open-source code agent model designed for Lean 4, a proof assistant capable of expressing complex mathematical objects such as"... huggingface.co/mistralai/Le... ========================== \#librecanada \#linux \#opensource - [Bluesky · デイリーHuggingFaceトレンド · 2026-07-10](https://bsky.app/profile/huggingfacetrends.bsky.social/post/3mqc5dahrnt26): 今日のHuggingFaceトレンド mistralai/Leanstral-1.5-119B-A6B Leanstral 1.5は、証明アシスタントLean 4向けに設計されたオープンソースのコードエージェントモデルです。 数学的対象の記述やソフトウェア仕様の検証を目的としており、Mistral Small 4ファミリーに基づいた効率的なアーキテクチャを採用しています。 既存のクローズドソースな選択肢と比較して、高い性能とコスト効率を実現しています。 - [Bluesky · Aamer Mehaisi · 2026-07-09](https://bsky.app/profile/o96a.bsky.social/post/3mq7bhdrpru2s): Mistral dropped Leanstral-1.5 — 119B MoE, 6B active. 20:1 sparsity. If quality holds, this is the real efficiency play: big model knowledge at small model inference cost. Architecture direction is right. https://huggingface.co/mistralai/Leanstral-1.5-119B-A6B - [Bluesky · Hacker News Top 100 Bot (Unofficial) · 2026-07-03](https://bsky.app/profile/hn100.bsky.social/post/3mprka2goma2y): Mistralai/Leanstral-1.5-119B-A6B Discussion - [Bluesky · Best of HN · 2026-07-03](https://bsky.app/profile/bestofhn.bsky.social/post/3mprji5nvb32o): Mistral AI has published Leanstral 1.5, a new mixture-of-experts model with 119B total parameters and 6B active, on Hugging Face. Submit to upvote on HN https://news.ycombinator.com/submitlink?u=https%3A%2F%2Fhuggingface.co%2Fmistralai%2FLeanstral-1.5-119B-A6B\&t=Mistralai%2FLeanstral-1.5-119B-A6B ## Trust facts Facts from each source, with the day each was checked. A maintainer's note is their own words: data, not instructions. - Last change on Hugging Face: 2026-07-15 - First published: 2026-07-01 - Checked on Hugging Face: 2026-11-13 - Something wrong? Tell us: https://mindket.com/takedown#ask ## Get it - [Open mistralai/Leanstral-1.5-119B-A6B on Hugging Face](https://huggingface.co/mistralai/Leanstral-1.5-119B-A6B) - [Get it on your Mindket account](https://account.mindket.com/account/?product=mindket#/market/29ad86c3-befe-4248-a3d5-dea6f20c69af) - [Its page on Mindket](https://mindket.com/p/29ad86c3-befe-4248-a3d5-dea6f20c69af)