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Mistral releases Leanstral 1.5, an open Lean 4 proof model

Sunday, July 5, 2026 · what moved in the AI release cycle in those 24 hours.

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Mistral's Leanstral 1.5 leads the day: an Apache-2.0 Lean 4 code agent model that reportedly solves 587 of 672 PutnamBench problems and catches real bugs in code. Anthropic news also stacked up, with export controls lifted on Claude Fable 5 and Mythos 5 and Fable 5 returning to service under temporary usage limits. Meanwhile, rumors point to a GPT-5.6 release in the coming weeks, with claims of more generous plan limits.

An AI summary of the day’s tracked items. It may contain errors; every item below links to its source.

Top stories

  1. 1

    Mistral AI Releases Leanstral 1.5: An Apache-2.0 Lean 4 Code Agent Model Solving 587 of 672 PutnamBench Problems - MarkTechPost

    An Apache-2.0 open model that solves 587 of 672 PutnamBench problems is a major step for formal verification and open-source releases.

    Leanstral 1.5 · Mistral AI

  2. 2

    Anthropic Says 'We're Grateful' as Trump Administration Lifts Export Controls on Claude Fable 5 and Mythos 5 After AI Security Standoff - Yahoo Finance

    The lifting of export controls on Anthropic's flagship models changes who can access frontier AI and ends a notable regulatory standoff.

    Claude Mythos 5 · Anthropic

  3. 3

    GPT-5.6 being prepared for release, already in the codex apps though not usable. Release next weeks seems highly likely. Let’s go! https://t.co/fLto61QFSo https://t.co/5rXKEE6XF0Rumor

    Signs of GPT-5.6 appearing in codex apps suggest an imminent OpenAI release, though this remains a rumor.

    ChatGPT 5.6 · @kimmonismus

Picked by AI from the day’s tracked items; every link goes to the source.

Crowd-guess shifts

Where the community’s average release-date guess moved since yesterday.

News & rumors added

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