Claude Opus 5 Released: How It Compares to Opus 4.8 and Fable 5
Anthropic released Claude Opus 5 on July 24, 2026, and its own documentation calls it a step-change rather than an incremental improvement over Opus 4.8 — yet the price does not move: $5 input / $25 output per million tokens, exactly half the flagship Fable 5 ($10 / $50). This article cross-checks the official announcement and documentation against several reports and lays out the core specs (claude-opus-5, a 1M context that is both default and max, 128K max output, knowledge cutoff May 2026), pricing including cache rates and fast mode (about 2.5x speed at 2x price, Claude API only), the benchmarks (Anthropic states in its own text that Frontier-Bench is more than double Opus 4.8, CursorBench 3.2 lands within 0.5% of Fable 5, ARC-AGI 3 is three times the runner-up, and OSWorld 2.0 beats Fable 5 at roughly a third of the cost; press-sourced figures read off the charts include Frontier-Bench 43.3%, ARC-AGI-3 30.2%, GDPval-AA 1,861 and OSWorld 70.6%), and the places it still loses (68.8% against GPT-5.6 Sol at 72.7% on DeepSWE v1.1, offensive security and long-horizon biology research where Mythos 5 leads, and settings where max effort scores below lower ones). It then covers the two breaking API changes (thinking is on by default, so tight max_tokens budgets get truncated; disabling thinking is only allowed at effort high or below, and xhigh or max returns a 400), how to pick among the five effort levels, new features such as mid-conversation tool changes, a 512-token cache minimum and default fallback mode, the personality shift toward longer answers, more narration, more delegation and unprompted self-verification — with the migration rule that you remove prompt text rather than add it — and finally who should migrate now, plus a six-step migration checklist.