DisclaimerUnofficial, and not affiliated with Anthropic. Nearly all of this is read straight out of what ships: npm bundles, captured prompts, published docs. Anthropic's own notes go in verbatim, marked as theirs. The rest is my reading, and every entry carries the strings behind it. If one looks wrong, vote it down and say why.
New __SYSTEM_PROMPT_DYNAMIC_BOUNDARY__ marker added for separating static and dynamic portions of system prompts, likely for improved prompt caching behavior.
Evidence
Constant at line 550046 (contains "__SYSTEM_PROMPT_DYNAMIC_BOUNDARY__")
Strings lifted out of the shipped bundle, so the claim above can be checked against them.
