The advisory shown to Pro-plan users running Opus who have consumed more than half their weekly limit now refers to Sonnet 5:
Before: "Sonnet 4.6 handles most coding tasks and uses your weekly limit roughly half as fast as Opus."
After: "Sonnet 5 handles most coding tasks and uses your weekly limit much more slowly than Opus."
Evidence
Opus usage advisory (search for "Sonnet 5 handles most coding tasks and uses your weekly limit much more slowly than Opus")
Strings lifted out of the shipped bundle, so the claim above can be checked against them.