{"rewrite":{"id":"r_a194224b4cebfff63edfe4bb","clusterId":"c_260e03c3e6f6a8439ede13ad","slug":"mistral-ai-releases-leanstral-1-5-for-lean-4-proof-assistance","model":"deepseek-v4-flash","headline":"Mistral AI Releases Leanstral 1.5 for Lean 4 Proof Assistance","summary":"Mistral AI released Leanstral 1.5 on June 30, 2026, an AI model for automated theorem proving and formalization with Lean 4. The 119-billion-parameter model uses a Mixture of Experts architecture with 6.5 billion active parameters and a 256k-token context length. It is available for free under Mistral AI's Labs framework, succeeding the March 2026 version.","whyItMatters":"Leanstral 1.5 aims to reduce the labor of converting human-readable math and specifications into Lean 4 notation, potentially broadening formal proof use beyond expert mathematicians to practical software verification.","webCardHtml":"\u003cp\u003eMistral AI released Leanstral 1.5 on June 30, 2026, a model designed to assist with automated theorem proving and formalization for the Lean 4 proof assistant. The model has 119 billion total parameters and uses a Mixture of Experts architecture, with 6.5 billion parameters active during inference. Its 256k-token context window can handle long proof files and related code together. Leanstral 1.5 replaces the original Leanstral, which launched in March 2026 and has been discontinued. The model is available for free on Mistral AI\u0026#39;s playground and supports API features including Chat Completions, Function Calling, and Agents \u0026amp; Conversations. Mistral AI has not yet published benchmarks comparing Leanstral 1.5\u0026#39;s performance to the earlier version, and weight release policies remain unconfirmed.\u003c/p\u003e","blueskyPost":"Mistral AI released Leanstral 1.5, an AI model for automated theorem proving and formalization with Lean 4. 119B params, 256k context, free in Labs.","twitterPost":"Mistral AI released Leanstral 1.5 for Lean 4 proof work. 119B params, MoE with 6.5B active, 256k context. Free in Labs. Replaces March version.","threadsPost":null,"newsletterBlurb":"Mistral AI released Leanstral 1.5 on June 30, an AI model for automated theorem proving and formalization with the Lean 4 proof assistant. The 119-billion-parameter model is available for free under Mistral AI's Labs framework and replaces the March 2026 version.","attributionJson":"[{\"source\":\"GIGAZINE\",\"url\":\"https://gigazine.net/news/20260701-mistral-leanstral-1-5/\",\"title\":\"Mistral releases 'Leanstral 1.5,' an AI for automated theorem proving, supporting Lean 4 proof work\"}]","lintFlagsJson":null,"lintHits":0,"costUsd":0,"inputTokens":4241,"outputTokens":617,"status":"published","repairAttempts":0,"nextRepairAt":null,"factsAttemptedAt":1782892850,"createdAt":"2026-07-01T07:52:32.000Z","publishedAt":"2026-07-01T07:54:50.000Z","updatedAt":"2026-07-01T07:54:50.000Z"},"cluster":{"id":"c_260e03c3e6f6a8439ede13ad","canonicalTitle":"Mistralが自動定理証明向けAI「Leanstral 1.5」リリース、Lean 4の証明作業を支援","representativeArticleId":"a_7f7b94f8a6793d70dc224ee9","sourceCount":1,"writtenSourceCount":1,"writeAttempts":0,"isSolo":true,"entitiesJson":"{\"anime_titles\":[],\"manga_titles\":[],\"work_titles\":[],\"studios\":[],\"people\":[],\"type\":\"news\",\"domain\":\"other\",\"is_roundup\":false}","contentType":"news","status":"published","firstSeenAt":"2026-07-01T07:05:00.000Z","lastSeenAt":"2026-07-01T07:05:00.000Z","updatedAt":"2026-07-01T07:54:51.000Z"},"attribution":[{"source":"GIGAZINE","url":"https://gigazine.net/news/20260701-mistral-leanstral-1-5/","title":"Mistralが自動定理証明向けAI「Leanstral 1.5」リリース、Lean 4の証明作業を支援"}],"entities":{"anime_titles":[],"manga_titles":[],"work_titles":[],"studios":[],"people":[],"type":"news","domain":"other","is_roundup":false},"keyFacts":["Mistral AI released Leanstral 1.5 on June 30, 2026, a model for automated theorem proving and formalization with Lean 4.","The model has 119 billion total parameters with a Mixture of Experts architecture, activating 6.5 billion parameters during inference.","Leanstral 1.5 features a 256k-token context window, allowing it to process long proof files and related code together.","The model is available for free on Mistral AI's playground and supports Chat Completions, Function Calling, and Agents \u0026 Conversations.","Leanstral 1.5 replaces the original Leanstral, which launched in March 2026 and has been discontinued."]}