Look into replacing `mypy` with `ty` once it is released

[fselmo]

Astral (builders of uv and ruff) are working on a type-checker, ty, that is currently in preview / alpha. Look into replacing mypy with ty once this is released as we could get significant performance gains from rust here.

[DeborahOlaboye]

Hi @fselmo , I’d love to work on this issue. Could you please assign it to me?

[SamWilsn]

A production-ready version of ty has not yet been released. I suppose you could do some research on what is/isn't working so far (and take some performance measurements), but I don't think it's ready for us to make the switch.

[DeborahOlaboye]

Alright, I'd do my research and revert. Thank you.

[fselmo]

It is worth noting here that ty does not currently have, nor seem to plan to add, support for pydantic type coercion. mypy has this via the pydantic.mypy plugin. Astral seems to want to align ty more with pyright than mypy in this sense and I believe that's their goal. This means we would have to be very explicit and instantiate every type that is passed in to every pydantic model rather than the repo allowing us to let pydantic do the conversion.

This sort of defeats a lot of the "devex" / ease-of-use parts of pydantic. This would be quite warranted for our specs side of things but it does burden quite a bit the testing package where we tend to benefit from the "pydantic magic".

For this reason, this may not end up being a desirable dependency for this repo, but it's still up in the air and should be discussed / researched further.

[danceratopz]

Thanks for the update @fselmo!!

I was curious so asked a friend to experiment with ty defaults on src/ethereum (which almost has no pydantic usage). It definitely is fast! Report summary below; more details: ty-execution-specs-experiment-src-ethereum.md.

Date: 2026-01-07
Git Ref: d618e5259a06179d7556af1961166cb7bc5da1e6
Versions: ty 0.0.9, mypy 1.17.0
Target: 1062 source files in src/ethereum

Key Findings

• ty finds 128 errors, mypy finds 0 — all ty errors are false positives or external library issues.
• ty is ~16x faster cold, ~3.5x slower cached than mypy.
• Conclusion All errors are false positives or stub issues. ty (v0.0.9) is too immature for this codebase's type patterns. Re-evaluate at v1.0+.
• Not recommended for this codebase until ty matures.

Performance Benchmark

Tool	Cold (no cache)	Cached
mypy	24.4s	0.26s
ty	1.5s	0.88s

ty's Rust implementation shows impressive cold-start performance (16x faster), but mypy's incremental cache is highly effective for iterative development (3.5x faster when cached).

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