The model constant has changed from opus47 to opus48 (claude-opus-4-8). This applies to the primary model slot across all providers.
Additionally, for Bedrock and Vertex sessions where only ANTHROPIC_DEFAULT_SONNET_MODEL has been customized (but not ANTHROPIC_DEFAULT_OPUS_MODEL), the system now intelligently falls back to Sonnet as the main model rather than forcing Opus — better matching admin intent when they configured only one model.
Evidence
Model constant opus48 added (search for "opus48") and provider-aware model selection (search for "CLAUDE_CODE_3P_PROBE_WROTE_SONNET_DEFAULT")
Strings lifted out of the shipped bundle, so the claim above can be checked against them.