They're two programs for running a Bitcoin node. Both follow the same rules, so they stay on the same network. They disagree on which unusual transactions, like large data inscriptions, to pass along before they're mined.
Go deeperBitcoin Core is the most widely used node software. In October 2025, Core version 30 raised its default limit on extra data in transactions (OP_RETURN) from about 80 bytes to 100,000 bytes, arguing the old filter didn't work. Bitcoin Knots keeps stricter filters, and many node runners switched to it in protest. These filters only affect what nodes relay, not what miners can put in blocks, so the choice mostly comes down to your values.