# YJIT

10 Hacker News commenters recommended YJIT and 2 criticized it, November 2025 to November 2026. It was recommended in 6 of 13 months. It meets the Hacker Approved badge rule.

**Verdict:** Built into Ruby, used in production, and gives performance gains for free. Critics note its profile-guided design pays a cost when hot paths change type.

## Why people recommend it

- Large performance gains for free (3 comments): "The former bringing a pretty substantial performance improvements to the language." ([source](https://news.ycombinator.com/item?id=48306449)) "you get performance improvement for free" ([source](https://news.ycombinator.com/item?id=46399379)) "Not really slow since YJIT, I think 3.1?" ([source](https://news.ycombinator.com/item?id=47822396))
- Proven in production at large sites (2 comments): "Ruby has had YJIT for some time and being deployed and used in production, from Github to Shopify." ([source](https://news.ycombinator.com/item?id=46344354)) "I just upgraded my prod apps to run on YJIT" ([source](https://news.ycombinator.com/item?id=46394938))
- Mature, well-regarded Ruby JIT (2 comments): "In Ruby-land we have had a good JIT for a while now" ([source](https://news.ycombinator.com/item?id=50259254)) "which will never be able to surpass Maxime's yjit" ([source](https://news.ycombinator.com/item?id=46014335))

## What people warn about

- Cost when hot paths diverge (1 comments): "YJIT's profile-guided approach is powerful but pays a cost every time a hot path diverges from the expected type." ([source](https://news.ycombinator.com/item?id=47474051))
- Being deprecated in favour of ZJIT (2 comments): "I'm a little sad to see YJIT go down in favour of a traditional design." ([source](https://news.ycombinator.com/item?id=46395716)) "Because now YJIT is deprecated" ([source](https://news.ycombinator.com/item?id=46395225))

## Alternatives hackers recommend

- [Numba](https://hackerapproved.com/p/numba.md): 30 recommend
- [CPython experimental JIT](https://hackerapproved.com/p/cpython-experimental-jit.md): 13 recommend
- [HotSpot JVM](https://hackerapproved.com/p/hotspot.md): 8 recommend
- [ZJIT](https://hackerapproved.com/p/zjit.md): 7 recommend
- [Mir JIT compiler library](https://hackerapproved.com/p/mir.md): 6 recommend

## Cite as

Hacker Approved, "YJIT", https://hackerapproved.com/p/yjit/ (counts from 1,795,640 Hacker News comments, November 2025 to November 2026).