PEP 803: Stable ABI for Free-Threaded Builds (packaging thread)

[encukou (Petr Viktorin)]

@pf_moore

I thought that “since Python 3.3” until now, we’ve only had one stable ABI, abi3. So comments about the compatibility of different stable versions makes no sense to me.

Well, you thought wrong :‍(
The Stable ABI is versioned, and it grew new (incompatible) additions in every single CPython version since it was introduced.

@pf_moore

it seems to be saying that the “stable build” will only be guaranteed compatible with two Python versions (i.e., for two years). That again doesn’t sound very “stable” to me…

Pardon the simplification, that was meant in a different context. I could instead say:

Stable ABI 3.n is compatible with the default build of 3.n+k, for all k.

That’s been the case since 3.2 (except some bugs along the way).

@pf_moore

clearly won’t be true at the point where free threading becomes the default build).

Yes. If and when free threading becomes the default, we’ll need to either break PEP 384’s promise or release Python 4.

@pf_moore

for free threaded builds there won’t be a stable ABI until development has settled down (and become the default), at which point we will introduce a stable free-threaded ABI

Per the Steering Council decision on PEP 779:

The Steering Council also expects that Stable ABI for free-threading should be prepared and defined for Python 3.15.

It has settled down (but obviously isn’t the default yet).