YJIT
Hacker ApprovedRanked 3 of 6 JIT compilers by recommenders
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.
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.
12 people gave an opinion
- recommend it
- 10
- criticize it
- 2
- approval share
- 83%
Recommended in 6 of 13 months
- November 2025: recommended
- December 2025: recommended
- January 2026: not recommended
- February 2026: not recommended
- March 2026: recommended
- April 2026: recommended
- May 2026: recommended
- June 2026: not recommended
- July 2026: not recommended
- August 2026: not recommended
- September 2026: not recommended
- October 2026: recommended
- November 2026: not recommended (month in progress)
Why it carries the badge
- 10 people recommend itNeeds 10 or more, met.
- 5 recommenders for every criticNeeds 2 to 1 or better, met.
- Recommended in 6 of 13 monthsNeeds 4 or more, met.
The same three rules apply to every product, and the badge can’t be bought. How the badge works
What people say about it
The reasons people give, with the number of comments that give each one. Open a reason to read what they said.
Why people recommend it
Each mark is one comment
Large performance gains for free
“The former bringing a pretty substantial performance improvements to the language.”
Comment from 28 May 2026 in “The Green Side of the Lua” “you get performance improvement for free”
Comment from 27 Dec 2025 in “ZJIT is now available in Ruby 4.0” “Not really slow since YJIT, I think 3.1?”
Comment from 19 Apr 2026 in “Optimizing Ruby Path Methods” Proven in production at large sites
“Ruby has had YJIT for some time and being deployed and used in production, from Github to Shopify.”
Comment from 21 Dec 2025 in “Ruby website redesigned” “I just upgraded my prod apps to run on YJIT”
Comment from 26 Dec 2025 in “ZJIT is now available in Ruby 4.0” Mature, well-regarded Ruby JIT
“In Ruby-land we have had a good JIT for a while now”
Comment from 27 Oct 2026 in “Python's experimental JIT to be removed” “which will never be able to surpass Maxime's yjit”
Comment from 22 Nov 2025 in “Ruby 4.0.0 Preview2”
What people warn about
Each mark is one comment
Cost when hot paths diverge
“YJIT's profile-guided approach is powerful but pays a cost every time a hot path diverges from the expected type.”
Comment from 22 Mar 2026 in “ZJIT removes redundant object loads and stores” Being deprecated in favour of ZJIT
“I'm a little sad to see YJIT go down in favour of a traditional design.”
Comment from 26 Dec 2025 in “ZJIT is now available in Ruby 4.0” “Because now YJIT is deprecated”
Comment from 26 Dec 2025 in “ZJIT is now available in Ruby 4.0”
Other JIT compilers people recommend
The four most recommended other JIT compilers, with the same counts for each, so you can compare like for like. The tick on each bar marks the 2 to 1 line the badge needs.
| Product | Recommend | Criticize | Approval | Months | Owned | Badge |
|---|---|---|---|---|---|---|
| Numba | 30 | 9 | 77% | 9 | — | Approved |
| CPython experimental JIT | 13 | 16 | 45% | 3 | — | — |
| YJITThis page | 10 | 2 | 83% | 6 | — | Approved |
| HotSpot JVM | 8 | 0 | 100% | 4 | — | — |
| ZJIT | 7 | 2 | 78% | 5 | — | — |
What people said
All 13 comments that mention it, newest first. Each links to the original comment.
“In Ruby-land we have had a good JIT for a while now”
“The former bringing a pretty substantial performance improvements to the language.”
“Not really slow since YJIT, I think 3.1?”
“YJIT's profile-guided approach is powerful but pays a cost every time a hot path diverges from the expected type.”
“you get performance improvement for free”
“I'm a little sad to see YJIT go down in favour of a traditional design.”
“Because now YJIT is deprecated”
“I just upgraded my prod apps to run on YJIT”
“Ruby has had YJIT for some time and being deployed and used in production, from Github to Shopify.”
“which will never be able to surpass Maxime's yjit”
“Methods that are written in pure ruby outperform C libraries called from Ruby”
“ZJIT is supposed to be an improvement on YJIT.”
“significant investment recently in JITs, in particular YJIT and ZJIT”
Counts come from 1,795,640 Hacker News comments, November 2025 to November 2026. How we count. Report a mistake.