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Leanstral

Mistral · Devstral & Leanstral line · coding · open weights

Released March 16, 2026Replaced by Leanstral 1.5Line discontinued Sep 30, 2026

Leanstral was released by Mistral on March 16, 2026, as an open-weights coding model in the Devstral & Leanstral line.

  • Release 4 of 5 in the Devstral & Leanstral line.
  • Came 97 days after Devstral 2, released Dec 9, 2025.
  • Replaced by Leanstral 1.5 on June 30, 2026, 106 days later.
  • Its usual gap between releases was about 102 days; the line's last release was on June 30, 2026.

What changed

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

Sources: Mistral AI · Hugging Face

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Where the Devstral & Leanstral line stands

Leanstral 1.5 is the current model in this line. The card shows how long it has been since the last release against the line's usual gap and its recent ones — the rhythm, not a date.

Devstral & Leanstral

Mistral · coding line · open weights

Latest: Leanstral 1.5 · Jun 30, 2026

DiscontinuedOfficially discontinued on Sep 30, 2026

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

What changed in Leanstral 1.5 →
Days since last release
116
days
Usual gap
102
days
Recent gaps
Leanstral 1.5 · Jun 2026
106
Leanstral · Mar 2026
97
Devstral 2 · Dec 2025
152
Devstral Medium · Jul 2025
50

Every Devstral & Leanstral release

Newest first. See the full line with every card →

  1. Jun 30, 2026Leanstral 1.5
  2. Mar 16, 2026Leanstral · this page
  3. Dec 9, 2025Devstral 2
  4. Jul 10, 2025Devstral Medium
  5. May 21, 2025Devstral