Anthropic has released a migration guide for developers transitioning to the Opus 5.5 model, addressing issues where autonomous agents stop prematurely. The guide clarifies that the model's tendency to provide frequent progress updates can be misinterpreted by legacy code as a task completion signal, leading to premature termination.
The official documentation identifies four common scenarios for these interruptions: excessive verbal summaries, unnecessary politeness, requests for human approval on non-critical decisions, and over-reporting. Anthropic recommends implementing task checklists, secondary validation models, and hard-stop mechanisms to ensure agents complete their objectives.
The migration to Opus 5.5 involves several API changes, including mandatory thinking parameters and updated tool-calling requirements. Developers must now handle 'thinking' blocks separately from standard text output. Failure to update these integration patterns can result in 400 errors or silent failures where the agent appears to hang.
Cost management in Opus 5.5 is now controlled via the 'effort' parameter, which offers five levels from 'low' to 'max'. Anthropic notes that Opus 5.5 performs more intensive reasoning than its predecessor at equivalent settings. Developers are advised to start with the 'medium' setting and adjust based on actual performance requirements.
For UI development, the guide suggests using negative constraints in prompts to avoid generic AI-generated aesthetics. Instead of requesting 'good design,' developers should explicitly list prohibited elements such as specific background colors, font styles, and button shapes to achieve more customized results.
