Questions

Phaethon is a runtime for the four Jak games, Jak and Daxter, Jak II, Jak 3 and Jak X: Combat Racing, each running natively on PC from your own disc. It began as a fork of OpenGOAL in September 2026, and its kernel, the core every game runs on, has since been completely rewritten. The renderer is Vulkan in place of OpenGL, it has a launcher of its own, and Jak X, which OpenGOAL never ported, plays from start to finish. Accuracy comes first: where the port and the PlayStation 2 disagree, the console is right. And nothing runs through a compatibility layer: the games' code talks to the machine's own interfaces directly.

Yes. Phaethon reads the files from your own disc of each game; it does not ship them, and no game data is distributed with the port. Jak X: Combat Racing and the Jak trilogy are owned by Naughty Dog and Sony Interactive Entertainment, and this project is not affiliated with either. See Getting started for how the launcher takes a disc image from there.

To install the runtime, yes. The launcher itself is a public download, but it downloads the runtime and its updates only for a signed-in Phaethon account. Once the runtime is installed, every game plays the same offline and signed out. An account also keeps your play time per game, summed across every PC you play on, and the launcher backs up your saves to it after each session.

All four are playable from start to finish. Jak X: Combat Racing has played from its first race to its credits since October 2026, and offline Exhibition mode works too; online play, Time Trials and ghosts do not work yet, and some event modes and menus still have pieces to bring up. Jak and Daxter, Jak II and Jak 3 run start to finish on OpenGOAL's decompilation, with this fork's retail-behavior fixes on top. Each game's page under the four cores says where it stands.

Retail-faithful means the port aims to do what the PlayStation 2 build did, frame for frame where it can: the same physics tick, the same field rate for the audio-synced cutscenes, the same heaps and load order. Faithfulness is the first of Phaethon's four goals, and the console is the reference whenever the port and the original disagree, so where the two differ, the console is treated as right.

The remastered preset is everything beyond retail: ray-traced shadows and remastered lighting, DLSS, DLAA and FSR 3.1 upscaling, a cutscene upscaler, a native widescreen picture with the HUD anchored to the edges instead of letterboxed, and motion blended at your display's own rate while every game still ticks at the disc's 60. It sits beside the retail and speedrun presets and never touches the retail one, so switching does not change what the faithful mode does. Settings and the remastered toggles shows where they live.

The launcher installs on Windows 10 and 11 and needs a graphics card with Vulkan 1.3. The games themselves also build and run on Linux, and a Linux build is checked on every change, but the launcher is a Windows application for now. The Steam Deck and macOS are on the roadmap.

Not yet. The game's own network code runs, but only over a loopback on one machine; nothing crosses a wire yet. Online multiplayer for Jak X is the next road on the roadmap.

Not in a first-class way yet. Custom levels, texture packs and GOAL-level changes work today as files placed by hand, as they do for OpenGOAL. A first-class mod API is on the roadmap: mods that install from the launcher, survive a runtime update and switch off as easily as they switch on.

Yes. Most of Phaethon's own work has been done with AI assistance, and every change, AI-assisted or not, is held to the same evidence standard and judged by what it does rather than how it was produced.

Two licenses cover Phaethon's code, by who wrote what. Phaethon's own work, everything added since the fork left OpenGOAL's jak-project, is under the PolyForm Strict License 1.0.0: you may use it, but you may not distribute it or make changes or new works based on it. The code inherited from OpenGOAL stays under the ISC License with the OpenGOAL Team's copyright notice, as that license requires.

The source is not released yet. It stays private until the work proves itself, and may be released then. The licenses it comes under, and the notices for what it builds on, are on the license page.

None of them sit inside Phaethon's own source. NVIDIA's DLSS headers and library are fetched at configure time, only when the DLSS build option is on. AMD's FSR SDK, MIT licensed, is cloned and built the same way, at the tag the build pins, v1.1.4 as of this writing. The debug window's two fonts, JetBrains Mono and Noto Sans JP under the SIL Open Font License, and its lucide icon face under the ISC License, ship as assets and load at run time. The cutscene upscaler's weights, Philip Hofmann's 2xNomosUni_compact_multijpg_ldl network, ship under Creative Commons Attribution 4.0, converted from float32 to float16 for the runtime but not retrained.

File a report from your account's report page, signed in with a verified email address, with what you saw, how to make it happen again, and the version of the launcher or the runtime. A security problem goes to security@playphaethon.com instead, as the security page says.

Neither. This fork does not send work upstream and does not take upstream's; it is its own line, and a problem with it is reported to this project rather than on OpenGOAL's own discussion board or Discord.

No, and it is not meant to be. The two shared a tree until September 2026 and have diverged since: Phaethon runs on its own rewritten kernel and a Vulkan renderer, builds each game with its own compiler, and its launcher installs only its own runtime. A game built by one does not run on the other, the launchers do not see each other's installs, and mods or texture packs made for one are not tested on the other. Save files are the game's own format in both, and nothing here has tested moving them. Anyone who wants OpenGOAL should use OpenGOAL; the two do not need each other.