Claude Sonnet 5 vs. Opus 4.8 vs. GPT-5.5: Full Pricing & Benchmark Comparison

Claude Sonnet 5 vs. Opus 4.8 vs. GPT-5.5: Full Pricing & Benchmark Comparison

If you've tried to pick an AI model this month, you already know the feeling: three companies, three release posts, three sets of benchmarks that all claim to be "the most agentic yet." I spent the past few days going through the actual system cards, pricing pages, and early developer reports for Claude Sonnet 5, Claude Opus 4.8, and GPT-5.5 so you don't have to. Here's what actually changed, what the pricing pages don't tell you upfront, and which model I'd reach for depending on what you're building. What Happened On June 30, 2026, Anthropic released Claude Sonnet 5, calling it the most agentic Sonnet-class model it has ever shipped. It became the default model for every Free and Pro user on Claude.ai starting July 1, and it's also live in Claude Code, the Claude Platform, and third-party tools like Cursor, GitHub Copilot, and VS Code. The launch lands in the middle of a genuinely wild few weeks for Anthropic: Claude Fable 5 had just been pulled o…