What
Two internal beta features register alongside the existing ones such as interleaved thinking and server-side fallback, both concerning promoting a prompt cache partway through a conversation. They use internal headers rather than dated public betas.
Details
- The registration helper only freezes a name and header pair; what decides whether the header is actually sent lives elsewhere in the request path.
Evidence
x-cc-internal-mid-conv-cache-promotion
Strings lifted out of the shipped bundle, so the claim above can be checked against them.