From the source
Today, we are making Claude Sonnet 5 available in Harvey.
Sonnet 5 is Anthropic's latest Sonnet model, building on Sonnet 4.6 with broad gains in legal accuracy and output quality across transactional and litigation work.
Sonnet 5 scored 5.8% all-pass on Harvey’s Legal Agent Benchmark (LAB), a strict evaluation that mirrors how multi-step legal work is executed at a law firm, from assignment through review.
The model showed strengths across a number of practice areas, including energy and natural resources, real estate, and capital markets — with drafting as its strongest LAB task type.
On BigLaw Bench, Sonnet 5 scored 91.3% — the highest we've recorded across both Sonnet and Opus models.
Its consistent performance across litigation and transactional work, combined with its cost efficiency, makes it especially well-suited for high-throughput tasks.
Risk assessment and compliance, case management, and transactional drafting were standout BigLaw Bench task types.
“ Sonnet 5 brings a meaningful jump in legal quality over Sonnet 4.6.
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