Claude Opus 5 vs Claude Sonnet 5.5

Where it leads

• Higher Arena Text score, 1492 Elo vs 1477 Elo
• Higher SimpleQA Verified score, 59.9% vs 46.5%

Best for

• Complex agentic coding and enterprise work as the general-purpose default before reaching for Fable 5.1
• Latency-sensitive work that can justify Fast mode pricing

Watch out for

• Fast mode pricing applies to the whole request, including above 200K input tokens, so it doubles the effective rate rather than adding a surcharge
• Cache reads are $0.50 per million (the standard 0.1x), five times Fable 5.1’s $0.25, even though Opus 5 is the cheaper model on base tokens. A cache-heavy agent loop can invert the expected cost ordering between the two.

Where it leads

• Lower input and output prices, $2 and $10 vs $5 and $25 per 1M tokens
• Higher Arena WebDev score, 1770 Elo vs 1691 Elo
• Higher FrontierMath Tiers 1-3 (v2) score, 88.8% vs 85.6%
• Higher GPQA Diamond score, 95.6% vs 93.9%
• Cheaper cached input, $0.10 vs $0.50 per 1M tokens
• Cheaper batch processing, $20 vs $50 for 10M input and 2M output tokens

Best for

• Production workloads that need frontier-adjacent quality at a mid-tier rate
• Latency-sensitive agent steps inside a larger pipeline

Watch out for

• Same list price as Claude Sonnet 5, so the gain is capability and cache economics rather than a cheaper rate card
• Anthropic positions Opus 5.5 rather than this as the default, so reach for Sonnet 5.5 when latency matters more than peak capability