Python's experimental JIT to be removed

[LWN subscriber-only content] Welcome to LWN.net The following subscription-only content has been made available to you by an LWN subscriber. Thousands of subscribers depend on LWN for the best news from the Linux and free software communities. If you enjoy this article, please consider subscribing to LWN. Thank you for visiting LWN.net! Python's experimental just-in-time (JIT) compiler, which was added to CPython in 2024 for the 3.13 release, is on its way out. In June, the Python steering council announced that it was pausing work on the JIT in CPython's main branch until there was an accepted Python Enhancement Proposal (PEP) that addressed concerns about maintenance, compatibility, and set clear success metrics as well as a timeline for completion. After creating PEP 836 ("JIT Go Brrr: The Path to a Supported JIT Compiler for CPython") to try to meet the council's request, and after months of discussion, the JIT maintainers have withdrawn the PEP. For now, it appears that development on the once-promising project has come to an end. The JIT was added to CPython by Brandt Bucher in early 2024. Generally, such a major feature would be expected to land only after the council had approved a standards-track PEP. Bucher had given a talk (YouTube video, slides) about the JIT at a Python core developer sprint, and announced his intent to merge the feature—but he had not taken the step of authoring or submitting a PEP for its approval. He was prodded into doing so by steering council member Thomas Wouters, who was also serving as the release manager for Python 3.13. Bucher and Savannah Ostrowski drafted PEP 744 ("JIT Compilation"), which was an informational PEP—meaning it only provides information to the Python community and does not represent formal consensus to proceed on a feature or project. LWN covered the discussion of PEP 744 in April 2024, and later covered Bucher's talk on the JIT at PyCon US 2024, as well as the follow-up talk at PyCon US 2025. PEP it up Work on the JIT had been proceeding on the basis of PEP 744 until this June, when the council had put forward its formal request for the JIT maintainers to create a standards-track PEP. One might wonder, as Antoine Pitrou did, why the council had decided that it was time to speak up and ask for a new PEP. Wouters said that there was no "single triggering event for this request", but that the council had been discussing the topic for a while and indicated that it was looking to ensure the JIT work …