Google migrates 40-year-old Fortran ocean model to Rust in 59 minutes with Gemini 4 Argon Google

Google engineers used Gemini 4 Argon inside the Google Antigravity development environment to migrate the core of FVCOM, a 174,000-line Fortran and C coastal ocean simulation, into 100% memory-safe Rust in 59 minutes. The migration workflow has been released as an open-source Antigravity skill.

Scientific simulations for climate, weather, and ocean modeling frequently rely on decades-old Fortran code that teams hesitate to refactor due to the risk of altering delicate numerical math. Using Antigravity's autonomous terminal execution and compiler loop, Gemini 4 Argon verified numerical parity against the original binaries without manual line-by-line translation.

What it is

• End-to-end migration. Antigravity executed the port across three autonomous phases: terminal baseline capture (11 min), whole-repo architectural blueprint (3 min), and closed-loop Rust translation with self-healing tests (45 min).
• Performance and efficiency. Simulation throughput increased by 1.88x, while peak memory usage dropped by 54% due to cache-friendly Struct-of-Arrays (SoA) layouts and zero allocations in inner loops.
• Decades-old bug detection. The agent caught six dormant bugs in the original Fortran and C code, including mesh index overflows, uninitialized memory reads on dry cells, and negative square-root calculations.
• Strict safety and testing. The migrated codebase enforces #![forbid(unsafe_code)] with zero unsafe blocks, achieves 96.8% branch test coverage, and matches original floating-point outputs to 12 decimal places across 100 randomized seeds.
• Automated self-healing. When an edge-case shallow-water test failed during the run, the agent analyzed the stack trace, corrected the vertical flux interpolation, and re-ran the suite autonomously.
• Open workflow. Google published the full migration pattern as an Antigravity skill invokable with /migrate-to-rust <repo-url>.

Sources

• Google Antigravity: Modernizing 40-year-old scientific code with Gemini 4 Argon