What is Phaethon and how is it different from OpenGOAL?¶
Phaethon is a hard fork of OpenGOAL's jak-project that ports Jak and Daxter, Jak II, Jak 3 and Jak X: Combat Racing natively to PC, built on OpenGOAL's decompilation of the original PlayStation 2 code. Two rules set it apart from the project it came from: no compatibility layer, ever, so the game's own code runs on the machine's own interfaces, Vulkan directly, the platform's own threads, files and sockets directly, rather than through a shim kept because removing it is work; and no unanswered TODO, so every deferral in the tree carries the issue that will close it, and a checker refuses a new one without one. This fork develops independently of upstream: it does not send work upstream and does not take upstream's.
Do I need to own the games?¶
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.
Which games are supported, and how far along is each?¶
Jak X: Combat Racing is playable: the story, the races and the arenas run, with bring-up work continuing on the remaining minigame and event roads, tracked on the bring-up milestone. Jak and Daxter, Jak II and Jak 3 all run, with retail-behavior fixes carried in this fork.
What does retail-faithful mean, and why is the console the reference?¶
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.
What is the remastered version, and does it change the faithful one?¶
The remastered version is everything beyond retail: higher frame caps (60, 120, 144), a native widescreen picture with the HUD anchored to the edges instead of letterboxed, texture packs, and DLSS or FSR upscaling. It lives entirely behind a toggle and never touches the retail-faithful preset, so turning it on or off does not change what the faithful mode does. See Settings and the remastered toggles for where the toggle lives.
Which platforms does Phaethon run on?¶
Windows is the platform it is built and played on daily. A Linux build compiles in continuous integration on every landing and boots. macOS and the Steam Deck are on the Roadmap.
Is there online play for Jak X: Combat Racing?¶
Not yet. Online multiplayer for Jak X is a Roadmap item rather than something the port ships today.
Can I mod it?¶
Not in a first-class way yet. Mod APIs are on the Roadmap.
Can I use AI to contribute?¶
Yes, and it is encouraged. Most of Phaethon's own work has been done with AI assistance, disclosed with an (AI-assisted) marker in the commit message, and every contribution, AI-assisted or not, is held to the same evidence standard and judged by what it does rather than how it was produced. Nobody is turned away for the tools they used.
Can I fork or redistribute it?¶
Two licenses cover this repository, 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 source exists to be read, built and played, not taken. The code inherited from OpenGOAL stays under the ISC License with the OpenGOAL Team's copyright notice, as that license requires.
What about the third-party parts, like DLSS, FSR, the fonts and the upscaler weights?¶
None of them sit inside this repository'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.
Where do I report a problem?¶
Through the issue forms: separate forms for a retail divergence, a crash or hang, a performance problem, a general bug, a feature request, tooling or CI, documentation, and an agent finding with its own evidence trail. See Reporting a retail divergence for how that form works field by field.
Does Phaethon send work upstream, or take work from it?¶
Neither. This fork does not send work upstream and does not take upstream's; it is its own line, and every issue and pull request for this code is tracked on this forge rather than on OpenGOAL's own discussion board or Discord.
Is Phaethon compatible with OpenGOAL?¶
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 kernel changes 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.