Which Claude Model for Which Job: Haiku, Sonnet, Opus and Fable for UK Business, With Prices (2026)
For a UK business the rule is to use the smallest Claude model that passes your own test on your own inputs, and to reserve the larger ones for the steps that need them. At September 2026 list prices Haiku 4.5 is $1 per million input tokens and $5 output, Sonnet 5 is $2 and $10, Opus 5.5 is $4 and $20 and Fable 5.1 is $10 and $50, about £0.75 to £7.55 per million input tokens. Haiku handles reading, sorting, extraction and routine replies; Sonnet handles most drafting and analysis; Opus handles long, careful reasoning and complex code; Fable is for the hardest problems where the cost is justified. From running production systems, the frontier model handles roughly one call in eighty and the small model does the rest, which is why the per-token headline overstates what a working system costs.
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