Changelog and versions

Pyro ships as one npm package, @povio/pyro, that holds the SDK, the pyro CLI and the native browsers. Every release is cut from a Git tag; this page lists the channels, the platforms, how to pin a version and what changed in recent releases.

Package

npm name	@povio/pyro
License	AGPL-3.0-only
Binary	pyro (node_modules/.bin/pyro)
Entry points	@povio/pyro (SDK), @povio/pyro/e2e (suite runner API), @povio/pyro/wright and @povio/pyro/test (Playwright drop-in)
Install scripts	None. The browsers are inside the tarball; nothing is downloaded at install time.

Check what you have installed:

bunx pyro version
# pyro X.Y.Z
# engine: JavaScriptCore; capabilities: Capabilities { ..., fork: true, ... }

fork: true means the browser was built against the patched JavaScriptCore and supports fork mode.

Release channels

npm dist-tag	Git tag	What it holds
latest	vX.Y.Z	Stable releases. bun add @povio/pyro installs this.
next	vX.Y.Z-rc.N or vX.Y.Z-rc	Release candidates. Publishing a stable version does not move next; it keeps pointing at the last RC.

@povio/pyro is published from the first release after the rename. To try the new names before then, see Before the first @povio/pyro release. Releases up to 0.0.33 are on npm as @povio/lightning-panda (there latest is 0.0.33 and next is the old 0.0.17-rc.1). Use next only when a release candidate is announced.

bun add @povio/pyro          # latest
bun add @povio/pyro@next     # newest release candidate
npm view @povio/pyro dist-tags

Platforms and runtimes

Platform	Browser in the package	Fork mode
macOS 14+ arm64 (Apple silicon)	native/darwin-arm64, patched JavaScriptCore	Yes
macOS 14+ x64 (Intel)	native/darwin-x64, system JavaScriptCore	No
Linux x64, glibc 2.39+ (Ubuntu 24.04, Debian 13, Fedora 40 or newer)	native/linux-x64, patched JavaScriptCore, ICU bundled in lib/	Yes
Linux arm64, glibc 2.39+	native/linux-arm64, patched JavaScriptCore, ICU bundled in lib/	Yes

Linux builds ship since v0.0.27 (on npm since 0.0.28). Release Linux binaries have no source-line debug information. The Intel macOS binary is checked in CI but not executed there.

On any other OS, or to use a browser you built yourself, use Pyro.connect() against a remote pyro serve, or set PYRO_BIN. The package has no os restriction, so it installs everywhere.

Runtime	Supported
Node.js	22 or newer (engines.node: ">=22")
Bun	Supported. Release CI tests the packed tarball with Bun 1.4.0; no minimum is declared.

Pinning a version

Versions are immutable on npm. Pin the exact version so a CI run and a laptop run the same browser:

bun add --exact @povio/pyro@X.Y.Z

{
  "devDependencies": {
    "@povio/pyro": "X.Y.Z"
  }
}

The browser binary is part of the package, so pinning the package pins the browser. pyro version prints the version the binary was built as; CI checks that it matches the tag.

Versions are 0.0.x: any release may change behaviour. Read the notes below before upgrading.

Release notes

Each tag vX.Y.Z creates a GitHub release named "Pyro vX.Y.Z" ("Rust Lightpanda vX.Y.Z" up to 0.0.33) in povio/pyro, with generated notes (the merged pull requests) and these assets:

Asset	Contents
pyro-rust-vX.Y.Z-macos-arm64.tar.gz	Browser on system JavaScriptCore, pyro-snapshot-compare, the client
pyro-rust-vX.Y.Z-macos-x64.tar.gz	Same, Intel
pyro-rust-vX.Y.Z-macos-arm64-fork.tar.gz	Browser with the patched JavaScriptCore (fork mode)
pyro-rust-vX.Y.Z-linux-x64.tar.gz, ...-linux-arm64.tar.gz	Linux browsers, ICU in lib/
povio-pyro-X.Y.Z.tgz	The npm package
pyro-jsc-source-vX.Y.Z.tar.gz	The patched JavaScriptCore source (LGPL)
SHA256SUMS.txt	Checksums of the assets

The repository is private at the time of writing, so the GitHub releases need repository access. The npm package is public.

A new version can take a while to appear on npm after its release: npm has listed versions up to about an hour after publication. If bun add @povio/pyro@X.Y.Z cannot find a fresh version, wait and retry.

Newer than 0.0.33

In the first @povio/pyro release (not on npm yet), on top of 0.0.33:

• Renamed to Pyro. The package is @povio/pyro and every name moved with it; see Renamed from Lightningpanda.
• Faster connection start and fork mode (#303): no JavaScript realm is created before a connection's first command; the fork template is forked from the server process.
• Engine reuse across connections (#304): a connection that made no page leaves its browser thread and engine to the next (--engine-reuse, PYRO_ENGINE_REUSE); the patched JavaScriptCore is linked statically (the arm64 macOS package no longer carries a lib/ directory beside the browser); memory is returned after pages close.
• Vendored engines updated (#302): Blitz, Taffy and Stylo 0.24.0.

Renamed from Lightningpanda

Pyro was called Lightningpanda up to 0.0.33. The rename changed every name, with no aliases, so update code, scripts and CI together when you move to @povio/pyro:

Up to 0.0.33	From the rename
@povio/lightning-panda	@povio/pyro
@povio/lightning-panda/playwright	@povio/pyro/wright
lightningpanda command	pyro
lightningpanda test	pyro run
lightningpanda e2e, serve, fetch, eval, version	pyro e2e, serve, fetch, eval, version
Lightningpanda class (Lightningpanda.launch, .connect)	Pyro (Pyro.launch, .connect)
Config file lightningpanda.config.*	pyro.config.* (playwright.config.* still works)
Playwright option use: { lightningpanda: {...} }, type LightningpandaOptions	use: { pyro: {...} }, PyroOptions
LIGHTNINGPANDA_BIN, LIGHTNINGPANDA_WS	PYRO_BIN, PYRO_WS (same meaning: the browser binary, a running server's endpoint)
LP_* variables of the Playwright runner (LP_CONFIG, LP_PROJECT, LP_RETRIES, LP_TIMEOUT, LP_UPDATE_SNAPSHOTS, LP_CONCURRENT)	PYRO_CONFIG, PYRO_PROJECT, PYRO_RETRIES, PYRO_TIMEOUT, PYRO_UPDATE_SNAPSHOTS, PYRO_CONCURRENT
LIGHTNINGPANDA_* variables of the browser (LIGHTNINGPANDA_STATIC, LIGHTNINGPANDA_FORK, LIGHTNINGPANDA_PARENT_PID, ...)	PYRO_* with the same suffix (PYRO_STATIC, PYRO_FORK, PYRO_PARENT_PID, ...)
CDP domains LP.* (LP.run, LP.act, ...) and Lightningpanda.* (Lightningpanda.acquirePreparedPage, ...)	one domain, Pyro.* (Pyro.run, Pyro.acquirePreparedPage, ...)
data-lp-* attributes (data-lp-handle, data-lp-frame, ...)	data-pyro-*
User agent compatible; lightningpanda/X.Y.Z	compatible; pyro/X.Y.Z
Release assets lightningpanda-rust-vX.Y.Z-*.tar.gz, povio-lightning-panda-X.Y.Z.tgz	pyro-rust-vX.Y.Z-*.tar.gz, povio-pyro-X.Y.Z.tgz
Release archive client folder lightning-panda/	pyro-client/
GitHub releases "Rust Lightpanda vX.Y.Z" in povio/lightningpanda	"Pyro vX.Y.Z" in povio/pyro (the old repository URL redirects)

A mechanical replace covers most projects: the package path first, then the names.

grep -rlE 'lightning-?panda|Lightningpanda|LIGHTNINGPANDA|data-lp-|\bLP[_.][A-Za-z]' --exclude-dir=node_modules --exclude-dir=.git . | xargs perl -pi -e '
  s#\@povio/lightning-panda/playwright#\@povio/pyro/wright#g; s#lightningpanda test#pyro run#g;
  s#lightning-panda#pyro#g; s#LIGHTNINGPANDA_#PYRO_#g; s#\bLP_(?=[A-Z])#PYRO_#g;
  s#\bLP\.(?=[a-z])#Pyro.#g; s#data-lp-#data-pyro-#g; s#Lightningpanda#Pyro#g; s#lightningpanda#pyro#g'

Then:

• Rename a lightningpanda.config.* file to pyro.config.* (the replace only edits file contents).
• Set the dependency to a real @povio/pyro version: the replace keeps the old version number ("@povio/pyro": "0.0.33"), which does not exist, and a lockfile entry rewritten this way no longer matches its tarball. Run bun add -d @povio/pyro so the lockfile is written again.
• Review the diff: the last rules also rewrite prose and unrelated LP_ names, and a release-archive path such as …/lightning-panda/ becomes …/pyro/, while the folder is now pyro-client/.

Version history

Releases up to 0.0.33 were published as @povio/lightning-panda; their notes below use the current names.

0.0.33 (2026-11-11)

• Fork mode: the root template compiles the app's ES modules once; forked pages load them without parsing (#301).
• Fork mode: the fork holds JavaScriptCore's timer thread and each forked child arms its own watchdog timer (#300).

0.0.32 (2026-11-11)

• New serve --hyphen-digit-breaks (PYRO_HYPHEN_DIGIT_BREAKS): Chrome's line break between a hyphen and a digit (#299).

0.0.31 (2026-11-10)

• PDF: variable fonts print at the weight and optical size they were shaped at (#294).
• PDF: glyphs substituted by OpenType features extract as their source text on page-box PDFs (#292).
• Fonts: @font-face unicode-range decides which face draws a character (#293).
• XML documents stop at each script (#296).
• WPT coverage gate on every pull request (#276, #295).

0.0.30 (2026-11-10)

• New pyro e2e suite runner: one process, one browser per suite (#289). See the runner guide.
• Shared profiles across clients of one serve --fork, serve lifetime fixes (#289).
• Fork mode: less CPU per forked page (fast exit, 32 MB JIT pool, JavaScriptCore heap growth) (#291).

0.0.29 (2026-11-10)

• Doubles cross CDP unchanged (float round-trip) (#290).

0.0.28 (2026-11-10)

• First npm release with the Linux browsers (smaller Linux payload).
• Fixed viewport invalidation on unstyled nodes.

0.0.27 (2026-11-10)

• Linux x64 and arm64 builds, in CI and in the GitHub release (#288). Not published to npm.

0.0.26 (2026-11-09)

• Module fetches are shared; service worker request ownership is preserved.

0.0.25 (2026-11-09)

• Fork IPC survives interrupted system calls.

0.0.24 (2026-11-09)

• A click's stability frames no longer wait an extra turn each (#287).

0.0.23 (2026-11-09)

• Bursts of cached resources no longer close CDP connections.

0.0.22 (2026-11-08)

• Playwright suites run on Pyro by swapping the import (#278). See Coming from Playwright.
• Web-platform gaps found by the WPT survey filled.
• PDF pagination at Chrome's speed (#282); incremental tables and upstream Blitz/Taffy/Stylo (#279); whole-program performance passes (#283-#286).

Earlier releases

Version	Date	Notes
0.0.21	2026-11-06	DOM, binding, CDP and style data maintained at mutation time (#274); deferred screenshot state preserved, passwords masked (#272)
0.0.20	2026-11-05	Release CI fix
0.0.19	2026-11-05	The npm package ships the fork-capable arm64 browser (#271); GitHub release assets built from the tag (#270). npm only, no GitHub release.
0.0.18	2026-11-05	DOM calls through the JITs, lazy startup (#268); WPT parity on the bench subset (#269); table layout fixes
0.0.17	2026-11-02	First npm release (published 2026-11-04)
0.0.17-rc.1	2026-11-04	Tag-based npm publishing; the current next
0.0.1 to 0.0.16	2026-10-20 to 2026-11-02	GitHub releases only