Moving from Claude Sonnet 4.6 to Sonnet 5.5 cuts the cost of the same text by about 13%, even after the roughly 30% token increase.
Moving from Haiku 4.5 to Haiku 5.5 cuts it by about 87%, while Opus 4.6 to Opus 5.5 costs about 4% more.
Anthropic says its newer tokenizer produces approximately 30% more tokens for the same text, and that the exact increase depends on your content.