Claude Opus 與 Sonnet 與 Haiku——完成任務的成本，而非 token 成本

# Cost per finished task, not cost per million tokens.
#
#   task_cost = step_cost x steps x attempts
#
# A step here is 25,000 input + 1,200 output tokens —
# one agentic round trip, sized the same way every cost page on
# this site sizes it.
#
#   Claude Haiku 4.5       $0.022 / step
#   Claude Sonnet 5        $0.043 / step
#   Claude Opus 5          $0.109 / step
#
# So the break-even is an ATTEMPT COUNT, not a price:
#
#   Claude Haiku 4.5 stops being cheaper than Claude Sonnet 5
#   once it needs 2.0x the attempts.
#
#   Claude Sonnet 5 stops being cheaper than Claude Opus 5
#   once it needs 2.5x the attempts.
#
# That is the whole decision. Everything else is judgement about
# how many attempts YOUR tasks take on each tier.

# The HAIKU line is required on Kunavo: unpinned, the haiku alias asks for an
# id Kunavo does not serve (Haiku 5.5 from v2.1.293), so /model haiku and
# haiku subagents 404. It also sends Claude Code's own background calls to
# Haiku instead of the main model.

export ANTHROPIC_MODEL=claude-sonnet-5
# The sonnet alias asks for Sonnet 5.5, which Kunavo does not serve:
# unpinned, /model sonnet, opusplan's execution phase and sonnet
# subagents 404.
export ANTHROPIC_DEFAULT_SONNET_MODEL=claude-sonnet-5
export ANTHROPIC_DEFAULT_HAIKU_MODEL=claude-haiku-4-5

# Same idea in any client with a per-role model field: strong model
# for the work, cheapest model for the housekeeping.