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Leanstral 1.5

Mistral · Devstral & Leanstral line · coding · open weights

Released June 30, 2026Line discontinued Sep 30, 2026

Leanstral 1.5 was released by Mistral on June 30, 2026, as an open-weights coding model in the Devstral & Leanstral line.

  • Release 5 of 5 in the Devstral & Leanstral line.
  • Came 106 days after Leanstral, released Mar 16, 2026.
  • The last release before the line was discontinued on September 30, 2026.
  • Its usual gap between releases was about 102 days; the line's last release was on June 30, 2026.

What changed

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

Sources: Mistral · 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
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 · this page
  2. Mar 16, 2026Leanstral
  3. Dec 9, 2025Devstral 2
  4. Jul 10, 2025Devstral Medium
  5. May 21, 2025Devstral