Python 3.14 Release Candidate 3: Final Preview Before Stable Version

Overview

Python 3.14.0rc3, the third and final release candidate for Python 3.14, has been officially released. This marks the last preview before the stable release scheduled for October 7, 2025. As a release candidate, it is nearly identical to the final version, with only critical bug fixes permitted from this point onward.

Magic Number Update in Bytecode

One notable change in this release candidate is an update to the magic number stored in Python bytecode (.pyc files). A bug was fixed that required bumping this value, meaning .pyc files created with rc2 are incompatible with rc3. They will be automatically recompiled when Python encounters them. This internal adjustment does not affect the ABI (Application Binary Interface), so wheels built for rc1 will work seamlessly with rc2, rc3, and future 3.14.x releases.

ABI Stability Assured

From this release forward, the ABI is frozen for the entire Python 3.14 series. This means that any binary extensions or wheels compiled against Python 3.14.0rc1 or later will remain compatible with the final release and all subsequent maintenance releases. Developers can confidently build and distribute wheels now without worrying about breaking changes.

Call to Action for Third-Party Maintainers

We strongly encourage maintainers of third-party Python projects to start testing and building for Python 3.14 during this release candidate phase. Publishing Python 3.14 wheels on PyPI now helps the ecosystem prepare for the final release. Benefits include:

• Ensuring your own libraries work with the new version.
• Helping downstream projects test their dependencies.
• Binaries built against any 3.14 RC will be compatible with the final 3.14.0 release.

If you encounter any issues, please report them to the Python bug tracker.

Important: This is a preview release. While it is extremely close to the final version, it is not recommended for production environments.

Core Developer Notes: Documentation Review

Core developers are asked to focus on documentation now. Verify that all changes are properly documented in the What’s New in Python 3.14 document. Check for any missing updates or undocumented changes that need to be added.

Major New Features in Python 3.14

Python 3.14 introduces several significant enhancements over Python 3.13. Below are the key highlights.

PEP 779 – Free-threaded Python

Free-threaded Python (also known as no-GIL) is now officially supported, allowing true parallel execution of threads without the Global Interpreter Lock. This is a landmark improvement for multi-threaded performance.

PEP 649 – Deferred Evaluation of Annotations

Annotation expressions are now evaluated lazily, improving semantics and eliminating forward-reference issues. This makes type hints more flexible and efficient.

PEP 750 – Template String Literals (t-strings)

A new string literal type, t"..." (template strings), allows custom string processing with familiar f-string syntax. This enables safer interpolation and domain-specific templating.

PEP 734 – Multiple Interpreters in the Stdlib

The standard library now includes support for multiple interpreters, making it easier to run isolated Python contexts within the same process.

PEP 784 – Zstandard Compression Module

A new module compression.zstd provides support for the Zstandard compression algorithm, offering high compression ratios and fast speeds.

PEP 758 – Except Expressions Without Brackets

Both except and except* expressions now allow omitting the parentheses, simplifying syntax.

CLI Enhancements

Syntax highlighting has been added to the interactive REPL (PyREPL). Additionally, color support is now available in the command-line interfaces of unittest, argparse, json, and calendar.

PEP 768 – External Debugger Interface

A zero-overhead external debugger interface for CPython allows debuggers to attach without performance penalty during normal execution.

UUID Version Support

The uuid module now supports versions 6 through 8, and generation of versions 3–5 is up to 40% faster.

PEP 765 – Disallow return/break/continue in finally

Using return, break, or continue that exits a finally block is now explicitly disallowed, preventing confusing control flow.

PEP 741 – Improved C API for Configuration

A better C API for configuring Python simplifies embedding and initialization.

New Type of Interpreter

An alternative interpreter, optimized for newer compilers, offers significantly better performance. This feature is opt-in and requires building from source.

Improved Error Messages

Many error messages have been refined to be more helpful and actionable.

Built-in HMAC with Formal Verification

A built-in implementation of HMAC now includes formally verified correctness, enhancing security and reliability.

Final Release Schedule

The next and final release of Python 3.14 will be 3.14.0, scheduled for Tuesday, October 7, 2025. Between now and then, only critical bug fixes will be applied. No ABI changes will occur.

For downloads and more details, visit the Python 3.14.0rc3 download page.