Leanstral 1.5

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Summary

Mistral AI releases Leanstral 1.5, an updated Lean 4 formal proof engineering model optimized for automated theorem proving and autoformalization, with 119B total parameters and 6.5B active parameters.

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# Leanstral 1.5 - Mistral AI Source: [https://docs.mistral.ai/models/model-cards/leanstral-1-5-26-06](https://docs.mistral.ai/models/model-cards/leanstral-1-5-26-06) ![Cat](https://docs.mistral.ai/_next/image?url=%2Fassets%2Fsprites%2Fcat_idle.gif&w=640&q=75) June 30, 2026 v1\.5 An updated Lean 4 formal proof engineering model optimised for automated theorem proving and autoformalization\. 119B total parameters, 6\.5B active\. Speed Performance Modalities Context 256k Price $0 Speed Performance Modalities Context 256k Price $0 ### Features [Chat Completions](https://docs.mistral.ai/studio-api/conversations/chat-completion) [Function Calling](https://docs.mistral.ai/studio-api/conversations/function-calling) [Agents & Conversations](https://docs.mistral.ai/studio-api/agents/agents-api) [Built\-In Tools](https://docs.mistral.ai/studio-api/agents/agent-tools) [Structured Outputs](https://docs.mistral.ai/studio-api/conversations/structured-output) [Predicted Outputs](https://docs.mistral.ai/studio-api/conversations/advanced/predicted-outputs) [Prefix](https://docs.mistral.ai/studio-api/conversations/chat-completion#other-useful-features) [OCR](https://docs.mistral.ai/studio-api/document-processing/overview) [Annotations \- Structured](https://docs.mistral.ai/studio-api/document-processing/annotations) [BBox Extraction](https://docs.mistral.ai/studio-api/document-processing/basic_ocr) [Document QnA](https://docs.mistral.ai/studio-api/document-processing/document_qna) [FIM](https://docs.mistral.ai/mistral-vibe/using-fim-api) [Embeddings](https://docs.mistral.ai/studio-api/knowledge-rag/embeddings) [Moderations](https://docs.mistral.ai/studio-api/safety-moderation) [Chat Moderations](https://docs.mistral.ai/studio-api/safety-moderation) [Transcriptions](https://docs.mistral.ai/studio-api/audio/speech_to_text) [Text to Speech](https://docs.mistral.ai/studio-api/audio/text_to_speech) [Timestamps](https://docs.mistral.ai/studio-api/audio/speech_to_text/offline_transcription#transcription-with-timestamps) [Batching](https://docs.mistral.ai/studio-api/batch-processing)

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