From Ancient Claude to Modern Claude: Model Migration Guide

TL;DR

Newer Claude models like Opus 5.5 and Sonnet 5.5 offer improved performance and reduced costs.
Users often face a dilemma when upgrading, as previous models are customized over weeks.
Personalization in Claude is largely stored externally in Memory, Projects, and Skills, not within the model itself.
Migrating to a new model requires transferring and cleaning these external components, not a complete retraining.
The process involves preparing the new model with information from the old setup before making changes.