# Why keep mimalloc 2.12? **URL:** \ **Category:** Core Development\ **Created:** [September 13, 2026, 6:53am UTC](https://discuss.python.org/t/why-keep-mimalloc-2-12/109040 "2026-09-13T06:53:17Z")\ **Posts on this page:** 3\ **Page:** 1
**Author:** ![clin1234](https://sea2.discourse-cdn.com/flex002/user_avatar/discuss.python.org/clin1234/32/20576_2.png) [@clin1234](https://discuss.python.org/u/clin1234)\ **Post date:** [September 13, 2026, 6:53am UTC](https://discuss.python.org/t/why-keep-mimalloc-2-12/109040/1 "2026-09-13T06:53:17Z")
Right now, the free-threaded interpreter relies on a heavily patched version of mimalloc 2.12. Is there a particular reason why this old version is kept, and why CPython hasn’t migrated to a newer 2.x version (currently 2.5.2), or adopted the 3.x branch? ---
**Author:** ![Stanfromireland](https://sea2.discourse-cdn.com/flex002/user_avatar/discuss.python.org/stanfromireland/32/10102_2.png) [@Stanfromireland](https://discuss.python.org/u/Stanfromireland)\ **Post date:** [September 13, 2026, 8:45am UTC](https://discuss.python.org/t/why-keep-mimalloc-2-12/109040/2 "2026-09-13T08:45:09Z")
See [python/cpython#113141](https://github.com/python/cpython/issues/113141). We have made _many_ changes to our vendored copy, so updating it is far from trivial. From what I know, there’s no particular reason we need to stay on the current version, it’s mostly a matter of someone doing the work. This also has to be weighed against the benefit it would bring us. We have selectively picked up patches for various bugs that affected us. ---
**Author:** ![methane](https://sea2.discourse-cdn.com/flex002/user_avatar/discuss.python.org/methane/32/43_2.png) [@methane](https://discuss.python.org/u/methane)\ **Post date:** [September 15, 2026, 3:50pm UTC](https://discuss.python.org/t/why-keep-mimalloc-2-12/109040/3 "2026-09-15T15:50:44Z")
I had Codex try updating mimalloc to v2.5.2. > > > See Objects/mimalloc/README.python.md for detail.