What
When Claude Code has a configured list of models, it turns the aliases opus, sonnet and haiku into a model ID from that list. Each alias now maps to the first entry of that family in the list.
Before, Claude Code preferred the canonical ID of the family, such as a claude- name or a dated ID, and only fell back to other entries when no canonical one was present.
Why
If you use a custom model list, for example through a gateway, the order of the list now decides which model an alias like opus uses. Check that the model you want comes first in its family.
Something disagreesSomething we can check disagrees with this entry, or the writer said they could not settle it.
The writer flagged doubt
It is not clear where the configured model list comes from or which features use this lookup.