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Stylus maturity assessment

A reference summary of Arbitrum Stylus as used by the PQ smart-account stack: what works well, what is rough, and what mitigations are in place.

What Stylus is​

Arbitrum Stylus is a WASM-based execution layer that runs alongside the EVM on Arbitrum. A Stylus contract is a Rust crate compiled to wasm32-unknown-unknown and deployed under a regular contract address. From Solidity it looks like any other contract — call it with standard ABI encoding, get standard returns.

For on-chain ML-DSA verification, Stylus is the only economically viable platform today (~374K gas versus millions in pure EVM).

What works well​

AreaDetail
Native Rust cryptoThe ml-dsa crate (RustCrypto) is used directly — no bindings, no translation layer
EVM interopSolidity calls Stylus and Stylus calls Solidity via standard ABI
CostWASM execution is 10–100× cheaper than equivalent EVM for crypto-heavy workloads
Production statusLive on Arbitrum One since September 2024; part of the mainline Nitro stack

Known issues​

Pre-1.0 SDK​

stylus-sdk-rs is pre-1.0. Two known issues affect common usage patterns:

  • Testing framework segfaults with mappings (stylus-sdk-rs#261). The verifier is stateless by design, so mappings are not used — this issue does not apply here.
  • Cross-contract return data loss (Nitro #4114). Affects scenarios where a Stylus contract initiates external calls and consumes return values. The Solidity → Stylus call direction is unaffected; the verifier does not initiate external calls.

The August 2024 OpenZeppelin audit of the Stylus SDK surfaced 2 Critical and 2 High findings, all addressed by the maintainers.

Contract auto-deactivation​

Stylus contracts auto-deactivate after 365 days or on ArbOS upgrades. A deactivated contract requires reactivation or redeployment before it can be called again. No built-in monitoring or automatic reactivation exists.

Mitigation: scheduled reactivation tracked as a calendar task.

Size limits​

MetricValue
Compressed size limit24 KB
Verifier gzipped size~7.8 KB
Raw headroom~3.3 KB

Adding multi-level ML-DSA support, batch verification, or a second implementation for cross-checking would require monitoring the size budget.

Tracing gaps​

cast run cannot trace Stylus transactions and returns OpcodeNotFound. For on-chain simulation use cast call; for EVM-side flows use forge test --fork-url.

Bundler simulation under ERC-7562​

ERC-4337 bundlers enforce ERC-7562 storage access rules during simulation. The validator module accesses a per-account public key in storage — compatible with the standard rules, but bundlers may impose stricter heuristics. Validated against Alto; Pimlico hosted and other production bundlers are on the integration roadmap.

Mitigations applied​

  • Stateless verifier. Reduces exposure to cross-runtime storage bugs; keeps the contract a pure function.
  • Pinned crate versions. ml-dsa and stylus-sdk are pinned; upgrades require re-running ACVP vectors and the bundler compatibility suite.
  • Solidity module owns storage. Public keys live in the Solidity module's mapping. If a storage-related SDK issue surfaces, it does not reach key material.
  • Cross-implementation tests. A test in the verifier suite uses @noble/post-quantum (TypeScript) to sign and the Stylus verifier to verify. If either side drifts, the test fails before deploy.
  • Calendar discipline for reactivation. Until tooling exists, the 365-day lifecycle is a tracked operational task.

What this means for adoption​

Stylus is mature enough to run a production cryptographic verifier. It is not mature enough to ignore the SDK changelog or skip the reactivation calendar. Build on Stylus, but plan for both.