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Messages API Now Supports Mid-Task Instruction Updates
Chris Harper
1 min read
May 29, 2026
AI
Developer Tools
LLM
Alongside Opus 4.8, Anthropic updated the Messages API to accept system entries inside the messages array. Developers can now update Claude's instructions mid-task without breaking the prompt cache or routing the update through a user turn. This is particularly valuable for long agentic runs where task context or constraints evolve.
Sources: Digital Applied