Anthropic made Claude Opus 5.5 , released on Tuesday, cheaper than its predecessor , cutting the price from $5 to $4 per million input tokens and from $25 to $20 per million output tokens. The 1 million-token context window and 128,000-token maximum output are unchanged. On paper, that makes upgrading an easy decision. In practice, it may not be as simple as changing the model ID. Anthropic’s migration guide flags four breaking changes that can cause requests built for Opus 5 to return 400 errors after switching to Opus 5.5. Several other changes won’t trigger an error but could still change...

Source: The New Stack