Pyrefly: all versions and old releases

*Release date：October 14, 2026*

Pyrefly v1.4.0 bundles **1191 commits** from **66 contributors**.

---

## Release Highlights

### Language Server

• **The VS Code extension now runs the Pyrefly from your environment.** By default, the extension launches the Pyrefly installed in your active Python environment (for example, your project's `.venv`), so your editor and your command line use the same version. If the environment has no Pyrefly, the extension falls back to its bundled binary. Set `pyrefly.pyreflyExecutable` to `bundled` to keep the old behavior. See [Pyrefly binary selection](https://pyrefly.org/en/docs/IDE/#pyrefly-binary-selection).

### Configuration & CLI

• **uv workspace members are now type checked.** In a uv workspace, the interpreter puts each member's source directory on `sys.path` as an editable install. Pyrefly treated those directories as installed packages and skipped them, so errors in workspace members went unreported. Pyrefly now checks editable sources inside your project, while regular `site-packages` stay excluded.

### Type Checking

• **Easier migration from BasedPyright.** Pyrefly reads `basedpyright` sections in `pyproject.toml` and applies the matching type checking mode preset.
• **New opt-in checks for untyped code.** New error kinds such as `unknown-member-type`, `unknown-return-type`, `untyped-function-decorator`, and `uninitialized-instance-variable` help you find where `Any` enters your code.

### Tensor Shapes

• **JAX shape stubs on PyPI.** This is the first stable release that ships JAX shape stubs as the `jax-pyrefly-stubs` package.

---

## ⚠️ Behavior Changes

These may change your editor setup or surface new errors in code that checked cleanly under v1.3.0.

• The VS Code extension now uses the Pyrefly in your active environment by default instead of its bundled binary. If your environment pins an older Pyrefly, the editor now runs that version. The **Pyrefly language server** output channel shows which binary was chosen and why.
• Pyrefly now checks the source of uv workspace members (editable installs inside your project). Errors in those packages that were hidden before can now appear.
• `--typeshed-path` now replaces the bundled typeshed entirely instead of overlaying it.
• The `incompatible-overload-residual` error kind is renamed to `incompatible-overload-argument`. The old name still works as a deprecated alias.
• `site-package-path` is renamed to `site-packages-path`. The old name still works.

---

## ✨ New & Improved

### Type Checking

• Pyrefly now recognizes `basedpyright` configuration sections in `pyproject.toml` and applies appropriate type checking mode presets, making it easier to migrate from BasedPyright.
• TypedDict handling has been significantly improved：generic `extra_items` are now instantiated correctly, extra items can supply missing arguments, and `definitely_seen` calculation in callable checking has been fixed.
• TypeVar restriction checking is now enforced even when the expected type is gradual, preventing silent violations of TypeVar bounds and constraints when `Any` appears in the expected type.
• Improved handling of overloaded function arguments in generic function calls through a new overload table mechanism, replacing the previous residual-based approach. The `incompatible-overload-residual` error kind has been renamed to `incompatible-overload-argument` (the old name remains as a deprecated alias).
• Variance inference has been improved with fixes for nested variance reliability bugs and explicit stored variance evidence.
• Property decorator validation now reports invalid signatures with extra required parameters.
• Added opt-in `uninitialized-instance-variable` check for annotated instance attributes never assigned in `__init__` or class body, including `@dataclass(init=False)` fields.
• Improved higher-order function call handling with quantified finalization and better overload branch capture.
• `functools.partial` now uses standard qua

*Release date：September 28, 2026*

Pyrefly v1.3.2 is a patch release that fixes regressions in how Pyrefly infers the type of a variable after it is assigned a value of type `Any`.

---

## 🐛 Bug fixes

• **#4846:** Fixed several regressions from v1.3.0 in type inference after a variable is reassigned to `Any`:
• Assigning an implicit `Any` (a value with no known type, such as the result of an unannotated function or an unresolved import) to an annotated variable once again produces `Unknown`. It no longer turns into an explicit `Any`.
• When a variable annotated as `Optional[T]` or `T | None` is narrowed to `None` and then reassigned inside that branch, Pyrefly no longer adds the annotation's `None` back after the branch. For example, `x：Any | None` followed by `if x is None: x = get_any()` now gives `Any` instead of `Any | None`.
• When a variable's annotation is a union that contains `Any`, assigning `Any` to it now narrows the variable to `Any`. For example, `x：Any | None` followed by `x = x or get_any()` now gives `Any` instead of `Any | None`, so later attribute access no longer reports a false `missing-attribute` error on `None`.

Thank-you to all our contributors who found these bugs and reported them! Did you know this is one of the most helpful contributions you can make to an open-source project? If you find any bugs in Pyrefly we want to know about them! Please open a bug report issue [here](https://github.com/facebook/pyrefly/issues).

---

## 📦 Upgrade

```bash
pip install --upgrade pyrefly==1.3.2
```

### How to safely upgrade your codebase

Upgrading the version of Pyrefly you're using or a third-party library you depend on can reveal new type errors in your code. Fixing them all at once is often unrealistic. We've written scripts to help you temporarily silence them. After upgrading, follow these steps:

1. `pyrefly check --suppress-errors`
2. Run your code formatter of choice
3. `pyrefly check --remove-unused-ignores`
4. Repeat until you achieve a clean formatting run and a clean type check.

This will add `# pyrefly：ignore` comments to your code, enabling you to silence errors and return to fix them later. This can make the process of upgrading a large codebase much more manageable.

Read more about error suppressions in the [Pyrefly documentation](https://pyrefly.org/en/docs/error-suppressions/).

*Release date: July 31, 2026*

Pyrefly v1.2.0 bundles **901 commits** from **59 contributors**.

---

## ✨ New & Improved

### Type Checking

Attrs classes are now fully supported with comprehensive field synthesis, validation, and special-method generation. Pyrefly recognizes `@attr.s`, `@define`, `@frozen`, and their variants, handling field specifiers (`attr.ib()`, `field()`), converters, validators, defaults, and private-field aliasing. Converters are typed from their real input type rather than `Any`, including the `@<field>.converter` decorator, `attrs.converters.pipe`, `attrs.converters.default_if_none`, and generic converters like `copy.deepcopy`. See the new [attrs documentation](https://pyrefly.org/en/docs/attrs/) for details.
`functools.partial` is now type-checked instead of treated as opaque. Bound arguments are validated at construction and Pyrefly synthesizes a precise residual signature for the remaining parameters, so errors surface at both the `partial(...)` call and the later invocation. Generic functions, overloads, constructors, bound methods, and `**Unpack[TypedDict]` parameters are supported, and results expose `.func`, `.args`, and `.keywords`. Precise residual callable assignment is enabled by the `strict` and `all` presets or explicitly with `strict-partial-subtyping`.
Functions decorated with `functools.singledispatch` now type-check calls using the signature of the function you decorated, and registered implementations are checked against that function's first parameter. Generic `singledispatch` functions infer from call arguments instead of reporting `Unknown`.
Pyrefly can now warn when a function declared to return a concrete type returns `Any`, with separate diagnostics for explicit and inferred cases. Off by default, and migrated automatically from mypy's `warn_return_any`.
Pattern matching is substantially more precise: positional class patterns resolve attribute names from `__match_args__` at solve time, sequence element captures read from the narrowed subject so sibling constraints refine them, and `isinstance` on a facet filters the parent union to matching members. Fully covered class and sequence patterns now subtract their union member from later cases.
Unpacking a variadic tuple with a fixed prefix and suffix no longer smears those elements into the starred capture, so `a, *rest, b = t` where `t: tuple[int, *tuple[bool, ...], str]` types `rest` as `list[bool]`.
TypedDict classes now synthesize `__required_keys__` and `__optional_keys__`, so protocols requiring them (like those in langgraph) satisfy structural checks. `.get()` and `.pop()` with literal defaults preserve the field type.
Overload handling improved throughout: constrained TypeVar arguments expand during resolution, rejected overloads no longer leak argument errors into diagnostics, and exact callback-forwarding signatures resolve overloaded callbacks against forwarded arguments for helpers like `asyncio.to_thread`.
Enum `.value` on an enum type now infers as the union of member literal values instead of widening to the mixed-in data type.
Lambda parameters are contextually typed more thoroughly. Types are stored directly rather than resolved through inference variables, and `*args`/`**kwargs` resolve from callable hints to `tuple[...]` and `dict[str, ...]` inside the body while preserving element types in the signature.
All properties are now treated as data descriptors, and reflected binary-operation dunders are tried first for proper subclasses, fixing a class of incorrect attribute and operator results.
Cyclic type aliases reachable from an annotation are now detected instead of hanging, and class finality is taken into account when deciding whether a condition is redundant.
Continued basedpyright parity work: class instance truthiness is recognized, code under `if TYPE_CHECKING` is handled consistently, `typing_extensions.sentinel` is supported with relaxed naming restrictions, and `super(cls, cls)` is accepted.
`copy.re

Release date: June 18, 2026

Pyrefly v1.1.1 is a patch release with a single bug fix.

-----

## 🐛 Bug fixes

- #3867: Fixed a regression introduced in 1.1.0 where isinstance() narrowing of a union variable
silently stopped working when an earlier sibling branch in the same if/elif/else chain narrowed
a different variable with isinstance() and returned. The later narrowing left the union
untouched, producing false missing-attribute errors on code that checked correctly in 1.0.0.

Thank-you to all our contributors who found these bugs and reported them! Did you know this is one
of the most helpful contributions you can make to an open-source project? If you find any bugs in
Pyrefly we want to know about them! Please open a bug report issue here.