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Leanstral 1.5: ICYMI: Mistral released Leanstral 1.5, a SOTA open model for Lean 4 proof engineering. > Developers use Lean 4 as a general-purpose functional language (for CLI tools and libraries)…

Mistral AI has not yet released Leanstral 1.5, a state-of-the-art open model for Lean 4 proof engineering, despite a social media post suggesting otherwise. The model is designed to help developers verify properties of code, protocols, and algorithms using Lean 4 as both a functional language and proof assistant. OutYet.ai continues to monitor Mistral AI's official channels for the release.

read1 min views1 publishedJul 4, 2026
Leanstral 1.5: ICYMI: Mistral released Leanstral 1.5, a SOTA open model for Lean 4 proof engineering. > Developers use Lean 4 as a general-purpose functional language (for CLI tools and libraries)…
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Mistral AILeanstral 1.5 No.

When is Leanstral 1.5 coming out? #

Leanstral 1.5 is not out yet. There is no announced date yet, and no firm estimate. OutYet.ai rechecks Mistral AI's official release surfaces every minute and flips this page the moment access goes live. Last checked Jul 4, 2026.

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[Compare Leanstral 1.5 with another model →](/compare?models=leanstral-1-5)

Also waiting on: [ChatGPT 5.6](/models/chatgpt-5-6), [Gemini 3.5 Pro](/models/gemini-3-5-pro), [Claude Fable 5.1](/models/claude-fable-5-1), [Claude Mythos 5.1](/models/claude-mythos-5-1)

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source & further reading
outyet.ai — original article Muse Spark: Meta is still training their big models but we will get an update on Muse Spark soon https://t.co/M62UrzO40q Llama 5: Meta's next frontier model 'Watermelon' reportedly caught GPT-5.5 on internal benchmarks (still training) Grok 3: Tesla Caps Employee AI Use To $200 A Month Except For Grok - AutoSpies.com
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