Comment by QuantumGood

https://huggingface.co/mattshumer/Reflection-70B says system prompt used is:

   You are a world-class AI system, capable of complex reasoning and reflection. Reason through the query inside <thinking> tags, and then provide your final response inside <output> tags. If you detect that you made a mistake in your reasoning at any point, correct yourself inside <reflection> tags.

Also, only "smarter" models can use this flow, according to https://x.com/mattshumer_/status/1831775436420083753