Fable 5 decodes a 1989 DOS game executable overnight in one day
u/PlayfulInterview984 used Claude's Fable 5 model to fully decode the Midwinter (1989) DOS executable overnight — mapping 602 functions and replicating the terrain generator in Python with bit-for-bit accuracy — a task that previously took weeks per system with earlier models.
Score breakdown
The overnight decode of a complete 1989 DOS executable — verified bit-for-bit — compresses what previously took weeks of work per system with earlier models into a single session, demonstrating a concrete step-change in AI-assisted reverse engineering of legacy software.
- 01Fable 5 decoded the entire Midwinter (1989) DOS executable overnight after earlier models took weeks per system
- 02602 functions were mapped and labeled, including terrain generator, vehicle physics, enemy AI, graphics formats, and audio system
- 03The terrain generator was replicated in Python with bit-for-bit matching output against the original game
u/PlayfulInterview984 has been remastering Midwinter — Mike Singleton's 1989 open-world DOS classic — for approximately six months, initially working in Rust/Bevy with Opus 4.2–4.7, then switching to Unreal Engine 5 with Opus 4.8 driving the build through MCP. Two days before posting, they turned on Fable 5 and directed it at the original DOS executable. Overnight, the model decoded the entire codebase: 602 functions were mapped and labeled, covering the terrain generator, vehicle physics, enemy AI, win/lose conditions, graphics formats, and the audio system. The terrain generator was replicated in Python, and its output matches the original game bit-for-bit. The author describes this as a dramatic leap over earlier models, for which extracting comparable ground truth took weeks per system — and some tasks were simply out of reach entirely.
The decode ran as parallel agents working through the disassembly with an evidence ledger.
The decode ran as parallel agents working through the disassembly with an evidence ledger. As an additional benchmark, Fable 5 was pointed at Star Command, a simpler 1989 DOS game, and replicated it in approximately one hour from raw disk files. The full decode has since been open-sourced under the MIT license on GitHub, including documentation, the 602-function ledger, tools, and replicas. A new asset extractor (`tools/extract_assets.py`) pulls approximately 600 sprites from a user's own copy of the game with correct CGA/EGA/VGA palettes. A playable tech demo and a detailed write-up on the decode process are available on the project site.
Key facts
- 01Fable 5 decoded the entire Midwinter (1989) DOS executable overnight after earlier models took weeks per system
- 02602 functions were mapped and labeled, including terrain generator, vehicle physics, enemy AI, graphics formats, and audio system
- 03The terrain generator was replicated in Python with bit-for-bit matching output against the original game
- 04The decode used parallel agents working through the disassembly with an evidence ledger
- 05Fable 5 also replicated a second 1989 DOS game, Star Command, in about one hour from raw disk files
- 06The full decode is open-sourced under MIT license, including a 602-function ledger and tools
- 07A new asset extractor (`tools/extract_assets.py`) pulls ~600 sprites with correct CGA/EGA/VGA palettes
Topics
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