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hydrogen-mvm

opened on May 21, 2026

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Documentation

Hello,

I want to know if the abi3-abi3t source level compatibility (not binary level compatibility) is largely done and extension authors can start compiling against 3.15.0b1 to port their source code over. I've found scant documentation on this, other than this demo repository: https://github.com/encukou/abi3-abi3t-universal/tree/b1

I have some extensions built on non-stable ABIs (3.11 and earlier) and one that's built for 3.14 (for free-threading). I want to port everything to the stable ABI, but I don't want to port to abi3 only to again have to do another port to abi3t, so I'm curious to know where things stand with abi3-abi3t and whether I can start leaping directly to it. The documentation isn't clear on this, other than just saying it's a new ABI and promoting its benefits. https://docs.python.org/3.15/whatsnew/3.15.html#whatsnew315-abi3t

I know I'll have to recompile when rc1 (or final) is out and that's okay, but I want to start the source level (C/C++ level) changes early (i.e. now) unless the devs know that source level compatibility is still in flux (like how PEP 820 changed the slot initialization).

Thanks.

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1. hydrogen-mvm

   added

   docsDocumentation in the Doc dirDocumentation in the Doc dir

   on May 21, 2026
2. github-project-automation

   added this to docs issueson May 21, 2026
3. github-project-automation

   moved this to Todo in docs issueson May 21, 2026
4. vstinner commented on May 21, 2026

   

   vstinner

   on May 21, 2026

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   cc @encukou
5. encukou commented on May 25, 2026

   

   encukou

   on May 25, 2026

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   Sorry for the (PyCon-related) delay.

   By beta 2 (i.e. next week) I'll have a PR with the migration docs; I don't know if it'll be merged by then. If I forget to link it here, please ping me.

   The implementation is done, except these docs (and internals like testing improvements & optimizations). Things may still change (up to release candidate) if unknown issues pop up, but that shouldn't invalidate your porting effort. We're not dropping another PEP 820; there's a chance you won't even need to recompile at rc1 :)
6. encukou commented on Jun 2, 2026

   

   encukou

   on Jun 2, 2026

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   The docs PR is up. Rendered version: https://cpython-previews--150580.org.readthedocs.build/en/150580/howto/abi3t-migration.html#abi3t-migration-howto

   Officially, things can change until the final release; the plan is that they don't.

   If you want to port, now is the best time to start -- if here are any issues, the sooner they're found the easier they are to fix.

   Reacted by hydrogen-mvm
7. encukou

   closed this as completedon Jun 2, 2026
8. hydrogen-mvm commented on Jun 25, 2026

   

   hydrogen-mvm

   on Jun 25, 2026

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   Thanks for the docs, I was able to get a single pyd file to load on both 3.15 and 3.15t while using the stable ABI. Thanks!

   Reacted by Petr Viktorin

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