>>102287993
Whelps, I finally signed up at Anthropic and gave them a CC.
Claude API returned error: 400 Bad Request
{"type":"error","error":{"type":"invalid_request_error","message":"messages: final assistant content cannot end with trailing whitespace"}}
Adding trailing newlines to prefill actually isn't possible, so no wonder it has no effect.
The two newlines thing in response is only because the model itself decided to, not because of an API thing.