JIT Planning for 3.15 and 3.16

Following a conversation at the CPython Core Dev Sprint, this is an uber issue tracking JIT performance goals and planning for 3.15 and 3.16.

The goal here is to capture our goals and the work that we believe is necessary to enable the JIT (on by default).

3.15 (May 2026)

Goals & "features"

Must Haves

5% faster (geometric mean)
- Best case: 50% faster
- Worst case: -10% faster
JIT coverage (i.e., how much code is being JIT'ted): 80% JIT coverage can be improved considerably #142982
Free-threading supported (pre-beta) Make the JIT thread-safe #133171 gh-141594: A free-threaded JIT (Part 1) #141595
Support for out-of-process profilers and debuggers Supporting stack unwinding in the JIT compiler #126910

Nice to haves

10% faster (geometric mean)
- Best case: 100% faster
- Worst case 1% slower
JIT coverage (i.e., how much code is being JIT'ted): 90%
Robust documentation

How will we do this?

Register allocation GH-135379: Top of stack caching for the JIT. #135465
More optimizations Better uop coverage in the JIT optimizer #131798 Eliminate redundant refcounting in the JIT #134584
Trace recording Trace recording JIT #139109
Code gen
LLVM 21 Update JIT builds to use LLVM 21 #140479
Warm up faster
More specialization Broader specialization in the Specializing Adaptive Interpreter for better JIT performance #143732

3.16

Goals & "features"

Must Haves

~ similar debuggability and performance across Tier 1 platforms
2+ maintainers in front-end, middle-end, and back-end
...Anything listed in 3.15 nice to have that was not achieved (e.g. docs, better coverage, faster)

How will we do this?

Unboxing (int/float/other types)
LLVM 22

Linked PRs

Here is link the issue related JITxFree-threadng: #133171

gh-139038: Add JIT What's New for 3.15 (#142845)

gh-139038: Add macOS performance numbers for the JIT (GH-143479)

gh-139038: Update JIT perf figures for 3.14a4 (GH-143705)

pythongh-139038: Update JIT perf figures for 3.14a4 (pythonGH-143705)

pythongh-139038: Add macOS performance numbers for the JIT (pythonGH-…

pythongh-139038: Update JIT perf figures for 3.14a4 (pythonGH-143705)

gh-139038: Link to Savannah's webpage for JIT results (#146013)

gh-139038: Update JIT results in preparation for 3.15a8 (GH-148018)

gh-139038: Credit more people for JIT in 3.15 (GH-148359)

gh-139038: Add whatsnew entry for jit unique reference tracking (GH-1…

pythongh-139038: Link to Savannah's webpage for JIT results (python#1…

pythongh-139038: Update JIT results in preparation for 3.15a8 (python…

pythongh-139038: Credit more people for JIT in 3.15 (pythonGH-148359)

pythongh-139038: Add whatsnew entry for jit unique reference tracking (…

gh-139038: Update final JIT figures for 3.15rc1 (#149210)

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JIT Planning for 3.15 and 3.16 #139038

3.15 (May 2026)

Goals & "features"

How will we do this?

3.16

Goals & "features"

How will we do this?

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JIT Planning for 3.15 and 3.16 #139038

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3.15 (May 2026)

Goals & "features"

How will we do this?

3.16

Goals & "features"

How will we do this?

Linked PRs

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corona10 commented on Sep 18, 2025

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