Claude Enables Mid-Session Agent Updates Without Cache Penalties

Long-running AI agents face a critical problem: injecting new instructions mid-session typically invalidates the entire prompt cache, forcing expensive full reprocessing. Claude's new mid-conversation system messages solve this by placing instructions after the cached history rather than editing the top-level prompt, preserving cache integrity while updating agent behavior. This approach also provides stronger security than user-message workarounds, preventing prompt injection vulnerabilities.