Tyk is written in Go and is optimized for performance. If your main requirement is performance you should probably take a look at Tyk, while Fusio has also a great performance it can not match with Tyk. At Tyk only the actual API Gateway is complete open-source, if you want to use the Developer-Portal or Backend-Admin UI component you need to buy a license. Tyk provides also a way to write plugins to add additional logic.
Fusio provides out-of-the box many actions to handle common endpoint logic and it is also easy possible to implement a custom logic. Fusio is completely open-source and we provide only one product which contains all features. Fusio also goes beyond the classical API Gateway feature scope and handles topics like API monetization and SDK generation.