Compatibility sets
A soft fork tightens validity rules, so blocks valid under the new rules remain acceptable to older nodes. Older nodes do not enforce the new restriction themselves.
A hard fork expands or otherwise changes validity rules in a way that older nodes may reject, requiring coordinated adoption to avoid a persistent chain split.
Activation and coordination
Deployment mechanisms can signal readiness or establish an activation point, but signaling is not a substitute for validation. Upgraded nodes enforce the new rules when activation conditions are met.
Operational risk
Operators must understand software versions, activation status and the rules they choose to enforce. Protocol changes are socio-technical events because software, miners, businesses and users must coordinate around predictable behavior.
Visual recap
Old and new validation sets
The direction of compatibility determines whether older nodes can follow upgraded blocks.
Proposed rule
Compatibility review
Deployment
Activation
Independent enforcement
Key takeaways
- Soft forks restrict the set of valid blocks.
- Hard forks can make blocks valid that old nodes reject.
- Activation coordinates when upgraded rules begin.
- Node operators ultimately choose the software and rules they enforce.
Lesson recap
Check what you learned
Reveal each model answer, then honestly mark whether you understood it or need another review.
1 of 3
Recall
Why can an old node usually continue following blocks produced under an activated soft fork?
References
