When Smarter Claude Breaks Your Tools: The Hidden Tradeoff in Model Upgrades
Reading Time: 4 minutesNewer Claude models Opus 4.8 and Sonnet 5 are reportedly sending extra, invented fields when calling custom tool schemas, breaking third-party coding tools that the older models handled correctly. Simon Willison’s analysis suggests this is a side effect of Anthropic training its latest models heavily on Claude Code’s native edit tool, creating a compatibility problem for any tool with a different schema.