Version 3.11 was not found in the local cache (actions/setup-python)

TL;DR: Use a Python version that actually has a prebuilt binary for your runner OS and architecture; check the versions manifest before pinning an exotic combo. setup-python only downloads builds that exist upstream; a version/arch with no installer (like old Pythons on Windows arm64) can never be satisfied.

Version 3.11 was not found in the local cache

The fix

1. Open the versions manifest and confirm your version/arch combo has a build: https://raw.githubusercontent.com/actions/python-versions/main/versions-manifest.json Expected: You see whether the combo exists.

2. Pin python-version to one that exists for your runner (e.g. 3.11 on ubuntu x64, or a newer 3.12+ for Windows arm64). Expected: The setup step downloads and installs cleanly.

3. If you must have that exact version, install Python yourself (apt, pyenv, or a container image) and skip setup-python. Expected: python --version reports what you installed.

When this applies

• actions/setup-python fails with Version X was not found in the local cache followed by a not-found error
• self-hosted runners or unusual architectures

When it does NOT apply

• the download itself times out (that is network flake; re-run)
• the version exists but extraction fails (that is disk space or permissions)

Compatibility

actions/setup-python v4/v5/v6 on GitHub-hosted and self-hosted runners, all OSes.

Variants of this error

Error: The version '3.9' with architecture 'arm64' was not found

The explicit arch form of the same failure. Same fix.

Version 3.12 with arch x64 not found

Older form from when 3.12 had no stable build yet. Same fix: pick a released version.

Why it happens

The runner's tool cache only holds what previous jobs put there; on a cold cache setup-python resolves the request against the python-versions manifest, and combos without upstream binaries (new architectures, brand-new or ancient versions) resolve to nothing.

Edge cases and pitfalls

• Ephemeral self-hosted runners always have a cold cache, so they hit the manifest on every run; pin versions that exist.
• allow-prereleases: true can satisfy requests for beta versions.
• Specifying 3.11 lets the action pick the latest 3.11.x with a build; pinning 3.11.0 exactly is more fragile.

Seen in actions/setup-python issue 976: requesting Python 3.9 on Windows arm64 fails with Version 3.9 was not found in the local cache and The version '3.9' with architecture 'arm64' was not found, because no binary installer exists for that combo. The verified fix is to use a version that ships installers for the runner arch. Source: https://github.com/actions/setup-python/issues/976