What happened.
The Leios integrated ledger had begun evaluating sub-transaction Plutus scripts and charging their execution units across every protocol version. In prototype 2026w38a, that behavior was reverted.
The issue surfaced as a ValidationTagMismatch Plutus failure on musashi. The release states that the behavior needs hard-fork or respin gating before it can come back.
Why it matters.
Execution-unit charging can change both a transaction’s cost and whether it validates. That makes the scope of the change important for builders considering assumptions around sub-transaction scripts.
For now, the relevant behavior has been pulled from the prototype ledger rather than restored without the stated gate. The cost model for these scripts remains unsettled until a gated version is published.
What to watch.
Watch the Leios prototype track for a release or ledger change that reintroduces sub-transaction Plutus-script evaluation behind a hard fork or respin. That would be the clearest receipt that the change is returning under the stated condition.
A future Leios release that explicitly restores the reverted behavior with hard-fork or respin gating.
Upstream references and independent checks
Digest dated 2026-09-23 · upstream model sonnet. Direct links are matched to all 1 upstream source IDs.
- 1Prototype 2026w38aDirect upstream source ·
7ea80a3de2ba5b13889b744a9c5c75f53d838837
This Research brief was generated by Terra from a dated upstream research digest. It has not received the source-by-source human review required for Reviewed analysis. Material limit: This is a single-source, prototype-ledger report: the change did not reach mainnet, and the source provides no scheduled hard fork.