What is the name of Perseverance's Earth-based test twin?

The name of Perseverance’s Earth-based test twin is OPTIMISM.

OPTIMISM is a full-scale vehicle system test bed built at NASA’s Jet Propulsion Laboratory in California. Its expanded name is “Operational Perseverance Twin for Integration of Mechanisms and Instruments Sent to Mars.” Engineers use it to test rover hardware, software, driving plans, autonomous navigation, drilling, and sample handling before sending commands to Mars.

The test twin is nearly identical to Perseverance, including its six-wheel mobility system, cameras, computers, robotic arm, and sample-caching equipment. It does differ in practical ways: Earth’s stronger gravity required thicker wheels, and OPTIMISM receives power through an umbilical connection rather than Perseverance’s nuclear radioisotope generator.

OPTIMISM operates in JPL’s Mars Yard, a rocky outdoor testing area designed to imitate Martian terrain. The name is also a deliberate companion to “Perseverance,” reflecting the mission team’s determination to find and solve problems on Earth rather than discover them after landing. MAGGIE, another test rover, is associated with Curiosity, not Perseverance.