Choose between Classic and Fusion by the execution workflow, not by treating one mode as a universal upgrade. Classic involves an ordinary swap transaction; Fusion asks resolvers to fill an order under its specified conditions. Available choices can depend on the assets, network and interface.
Where the user pays attention
| Question | Classic | Fusion |
|---|---|---|
| What do I track? | The submitted transaction. | The order and any resulting fills. |
| How do I review cost? | Quoted output plus separate transaction/setup costs. | Received amount and any approval setup. |
| What if execution does not happen? | Inspect whether the transaction is pending or failed. | Inspect whether the order remains active or has expired. |
The Fusion guide describes resolver competition through an auction. An order that attracts no fill can expire. This makes the deadline part of the trade instruction, not a decorative countdown.
Gasless still has a setup boundary
According to the current starting requirements, Classic needs native assets for gas. Fusion execution costs affect the amount received, while initial contract permissions can still need native gas. A wallet holding only the sell token therefore needs a quote-specific approval check.
Compare the final output and the complete sequence of authorizations. If changing modes asks for a new spender approval, review that request on its own merits. An approval previously granted for another contract does not establish permission for the new one.
Which workflow fits?
Classic may fit an application expecting a transaction that the user submits and monitors directly. Fusion may fit a user who prefers resolver-paid execution and can accept the order's timing conditions. These are workflow reasons, not evidence of a consistently better rate.
Before retrying elsewhere, establish the first instruction's status. A still-valid order is different from a transaction that definitely reverted. Keeping both active unintentionally can change the total amount you end up selling.
Sources & verification (2)
Source-check date is recorded in the article details. URLs are provided for manual verification. Use Copy to keep this page open.
- What is 1inch Fusion, and how does it work?
Resolver-filled auction orders, expiry and partial fills.
https://help.1inch.com/en/articles/6796085-what-is-1inch-fusion-and-how-does-it-work - What do I need to start swapping on 1inch?
Third-party wallets supported; Classic needs gas; Fusion setup can need native gas and execution costs affect output.
https://help.1inch.com/en/articles/4585059-what-do-i-need-to-start-swapping-on-1inch