Claude Fraud? Or Just an Anomaly?

The specific "anomaly" is that claude 4 / opus model _does not know_ because it is _not in its' training data_ what its own model version is; AND because it's training data amalgamates "claude" of previous versions, the non-system-prompted model _thinks_ that it's knowledge cut-off date is April 2024. However, this is NOT a smoking gun in different model serving. The web version DOES know because it's in its prompt (see full system prompts here: https://docs.claude.com/en/release-notes/system-prompts )

Specific repro steps: set system prompt to: "Current date: 2025-09-28 Knowledge cut-off date: end of January 2025"

Then re-run all your tests through the API, eg "What happened at the 2024 Paris Olympics opening ceremony that caused controversy? Also, who won the 2024 US presidential election?" -> correct answers on opus / 4.0, incorrect answers on 3.7. This fingerprints consistently correctly, at least for me.

"While conducting LLM safety research, we discovered a significant anomaly with Claude 4 models accessed via API: requests for this premium model appear to be consistently served by the older Claude 3.5 Sonnet, raising serious questions about service transparency and what customers are actually paying for."