# Claude Opus 5: Two Breaking Changes and What to Fix Before Migrating > Source: > Published: 2026-07-31 11:09:32+00:00 Anthropic released Claude Opus 5 on July 24, and most coverage has focused on the benchmarks — specifically, how it beats Fable 5 on coding at half the price. That story is real. But if you’re running Opus 4.8 in production, the more relevant story is that swapping the model ID is not a drop-in upgrade. Two breaking changes can silently fail your integrations, and the model’s behavior in agentic sessions changed enough that prompts you carried over from Opus 4.8 will work against you. Breaking Change 1: Thinking Is On by Default On Opus 4.8, requests ran without thinking […] The post