What Is the Concept of a “Soft Fork” and How Does It Relate to Block Immutability?

A soft fork is a backward-compatible protocol upgrade, meaning older nodes that have not upgraded will still see the new blocks as valid, though they may not fully understand the new rules. It typically enforces stricter rules on the block structure or transaction types.

It relates to immutability by demonstrating that while the past ledger is immutable, the rules for future block creation can be upgraded without breaking consensus for non-upgraded nodes.