ZEUS uses hodl invoices, which are A) somewhat unreliable and B) harmful to the Lightning Network, as they lock up channel liquidity.
Spark takes a different approach. It doesn’t use hodl invoices. Instead, when someone sends you a Lightning payment, it’s auto-swapped into Spark. Then, when you come back online, you co-sign with the Spark operator to regain full control of your funds via a combined key.
The main difference is in the trust model: ZEUS is fully non-custodial and trustless, while Spark introduces a 1-of-N trust assumption—only one honest Spark operator is needed to keep your funds secure.
