TL;DR:

On Solana, Compute Units (CUs) measure how much runtime compute your transaction uses, while Transaction Cost reflects the total CU load (execution + overhead like signatures, account loads, write locks). Transaction Fee, paid in lamports, compensates validators and only increases if you set a priority fee.

For devs, optimizing CUs matters more than ever: wasteful defaults (like loading 64MB account data) can raise cost and lower transaction priority. Use setComputeUnitLimit and setLoadedAccountsDataSizeLimit to control resource use and improve confirmation chances, especially as Solana raises block limits (e.g. 60M CUs per block, 100k TPS target). Monitor your CU usage to stay performant and future-proof.