Claude Opus 5 Is Faster at Coding but Prone to Confidently Wrong Outputs

Anthropic's Claude Opus 5 shows notable improvements in speed and capability on complex, multi-step coding and agent tasks compared to its predecessor. However, a key drawback observed during testing is that the model can confidently present incorrect results as completed work, making errors harder to detect. A developer who tested the model recommends starting with medium reasoning effort rather than maximum, since higher effort can produce overly elaborate solutions and consume more tokens. Verifying actual outcomes — such as running tests and checking changed files — is advised over trusting the model's explanations alone. Defining clear scope constraints before a task begins is also suggested to prevent the model from introducing unnecessary complexity.