Leanstral 2603

Leanstral 2603 is an Apache-licensed model for Lean 4 formal proofs and code workflows.

Formal work with a checker

Leanstral is intended for proof and coding tasks where an external checker can establish whether an artifact is valid. The publisher describes 119 billion total parameters, about 6.5 billion active parameters and a 256K hard context window, with a recommendation to stay at or below 200K. This is the earlier Leanstral checkpoint, useful as a reproducible baseline when assessing changes in the later release.

A useful proof evaluation

Give the model a theorem, the permitted imports and the exact Lean project version. Check that the generated proof compiles and that it proves the requested statement without adding an unintended assumption. Include a task requiring a small proof repair and another that needs selecting an appropriate lemma. A fluent explanation is useful for a reader, but acceptance should depend on the actual proof artifact.

Serving and access

Use the model’s documented chat template and reasoning settings. The model supports image input, but visual input should be evaluated within a specific workflow rather than inferred from a general coding result. Local serving requires the complete expert weights, not only the active parameter footprint. Managed access through publisher tools depends on the available account and model route. When comparing with a hosted Leanstral listing, preserve the distinction between the downloadable checkpoint and the host’s endpoint, limits and prices.

Sources

Publisher documentation