Options traders who bet the Trump administration would renege on its promise to tariff raw copper imports are cashing in big.

Copper traders were caught flat-footed after refined copper was exempted from Trump's new tariffs. The exemption triggered a 20% drop in copper futures on the COMEX exchange. Traders now face excess inventory, with COMEX stockpiles at a 21-year high.

The 50% tariff on imported copper that starts Friday excludes a critical input that companies say they can’t get enough of in the U.S.: cathodes. Here's what you need to know. What are cathodes? Cathodes are a key intermediate product in copper manufacturing.