Claude Sonnet 5

Model id claude-sonnet-5. Drop-in upgrade for Sonnet 4.6: adaptive thinking on by default, manual extended-thinking removed (400 error), new tokenizer (~30% more tokens for same text vs Sonnet 4.6), non-default sampling params rejected. Introductory pricing $2/$10 per MTok through 2026-08-31, standard pricing $3/$15 thereafter (used here). On Terminal-Bench 2.1 and GDPval-AA v2 it narrowly beats Opus 4.8 despite Sonnet-tier pricing. NO SEPARATE '(High)' PRODUCT: Anthropic's docs state explicitly that setting effort to 'high' 'produces exactly the same behavior as omitting the effort parameter entirely,' and high is the documented default — there is no distinct marketed 'Sonnet 5 (High)' SKU to add as a sibling entry. Pricing correction (Oct 2026): Sonnet 5 launched at $2/$10 per MTok and Anthropic made that the standard price on Aug 10, 2026, cancelling the planned Sep 1 increase to $3/$15, so $3/$15 was never charged.