Module pricing 

Centralised pricing logic for Anthropic models.

All cost calculations live here so that the engine, TUI, and any future consumer share a single source of truth. Update this file — and only this file — whenever Anthropic changes its pricing.

Prices are in USD per million tokens (as of 2026-06). Source: https://www.anthropic.com/pricing

Model	Input	Output
Fable	$10.00	$50.00
Opus	$5.00	$25.00
Sonnet	$3.00	$15.00
Haiku	$1.00	$5.00

Cache pricing (relative to input price):

• Cache reads: 0.10× input price (prompt-cache hit)
• Cache write (5m): 1.25× input price (5-minute TTL, the default)
• Cache write (1h): 2.00× input price (1-hour TTL, opt-in via cache_ttl)

Functions

calculate_cost

Calculate the USD cost of a single model turn (no cache-write TTL split).

calculate_cost_optional_split

Split-aware cost for callers holding an aggregate plus an optional TTL split (the shape of SessionEvent::Usage). When either split bucket is present the split rates apply; when both are None, the aggregate is billed at the 5m rate — fail-cheap, never fail-expensive.

calculate_cost_split

Calculate the USD cost of a single model turn with the cache-write TTL split made first-class.