Devstral & Leanstral

Mistral · coding line · open weights

4 releases since 2025Latest: Leanstral 1.5

Where the line stands

How long it has been since the last release against the line's usual gap and its recent ones — the rhythm, not a date.

Mistral · Devstral & Leanstral line · coding · open weights

Mid-cycle69 of ~108 days into its usual cycle

Apache 2.0 model for Lean 4 proof engineering with 119B parameters and 6B active, solving 587 of 672 PutnamBench problems.

Days since last release

Leanstral 1.5 · Jul 2, 2026

days

Usual gap

108

days

Recent gaps

Leanstral 1.5 · Jul 2026

108

Leanstral · Mar 2026

Devstral 2 · Dec 2025

202

Newest first — what each version changed versus the one before, in Mistral's own numbers.

Jul

Apache 2.0 model for Lean 4 proof engineering with 119B parameters and 6B active, solving 587 of 672 PutnamBench problems.

Mar

An open-weight (Apache 2.0) code agent for the Lean 4 proof assistant that generates code and formally proves implementations against specifications.

Dec

May

One email a week: what AI models shipped, the actual differences vs the previous version, and what's coming next. No filler.