Sonnet 5 review: I ran 64 generations to find out if it's worth it

I’ve been testing every major frontier model release since the start of the year, and when Anthropic dropped Sonnet 5, I wanted more than a vibe check. I got tired of one-off tests I couldn’t repeat or compare over time, so I built something better: the How I AI Bench, a repeatable eval harness I constructed live using Claude Code while recording this episode. I ran Sonnet 5 blind against four other frontier models (Sonnet 4.6, Opus 4.8, GPT-5.5, and Gemini 3 Pro) across PRD quality, prototype generation, agentic task completion, and agent personality. The results were not what I expected.

What you’ll learn:

What Anthropic claims Sonnet 5 improves over Sonnet 4.6, and where the benchmark data actually backs that up
How I built the How I AI Bench in under 45 minutes using Claude Code, starting from my own stored session history
Why I combined human vibe scoring (70%) with LLM as judge scoring (30%) instead of trusting either alone
How to set up a local HTML scoring page so you can rate AI outputs on gut feel and export those scores as JSON
Which model I recommend for PRDs, which for complex prototypes, and which for chatting with an agent daily

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In this episode, we cover:

(00:00) Sonnet 5 is out

(01:55) What Anthropic claims

(04:02) Why I’m done with one-off vibe checks

(05:05) Building the How I AI Bench live with Claude Code

(07:42) The scoring system

(10:43) Agent voice eval