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Official reference — The official costs docs and model configuration docs cover pricing, caching, and the CLAUDE_CODE_SUBAGENT_MODEL setting. This page adds the opinionated routing strategy.

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The Cost Reality

ApproachApproximate cost multiplierWhen it’s worth it
Single session1x (baseline)Sequential tasks, focused work
Subagents4-7xParallel research, independent file edits
Agent Teams~15xTasks requiring inter-agent coordination
The overhead comes from each agent loading project context independently, every message consuming tokens in both sender’s and receiver’s context, and broadcasts multiplying cost by teammate count.

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Model Routing Strategy

The most impactful cost optimization: use the cheapest model that can do the job at each stage.
StageModelWhy
Research / explorationHaikuFast, cheap, only needs to read and summarize
ImplementationSonnetGood balance of capability and cost
Architecture / coordinationOpusComplex reasoning, big-picture decisions
ValidationSonnetNeeds to understand code, doesn’t need to generate much
Example pipeline: 
Research (Haiku) → Plan (Opus) → Implement (Sonnet) → Validate (Sonnet, read-only)

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The opusplan Pattern

Official reference — For model aliases, /model switching, and CLAUDE_CODE_SUBAGENT_MODEL, see the official model configuration docs. This section covers the routing strategy.
The highest-leverage cost optimization: Opus plans, Sonnet executes. Use Opus for architecture decisions and coordination, then route implementation to Sonnet agents. This cuts 60-80% of token costs while maintaining quality where it matters.
TechniqueHowSavings
opusplanOpus plans + Sonnet implements60-80%
Mid-session /model switchStart with Opus, switch to Sonnet for execution40-60%
think harder / ultrathinkExtended thinking on Sonnet instead of switching to Opus~80% vs Opus
Haiku for researchRoute exploration agents to Haiku via model: haiku in agent frontmatter90%+ vs Opus
The key insight: model choice is a per-task decision, not a per-session one. Switch models as the work shifts from reasoning to execution.

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Practical Tips

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Minimize context pollution

  • Verbose output degrades agent performance and burns tokens. Keep agent prompts focused.
  • Use the Explore agent (Haiku, read-only) for broad searches instead of having your main Opus session read dozens of files.

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Speed up test suites

  • Include --fast options for test suites in your CLAUDE.md — agents waste time running full suites when a subset would suffice.
  • Route test-running agents to Sonnet; they don’t need Opus-level reasoning.

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Structure CLAUDE.md for multi-agent

  • Include module boundaries so agents know which files they own.
  • List verification commands so every agent can self-check.
  • Mark shared files (e.g., package.json, tsconfig.json) as “coordinate before editing.”

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Use /batch for independent work

/batch is dramatically cheaper than Agent Teams for work where agents don’t need to communicate.

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Reference: Real-World Scale

For perspective: Anthropic’s C compiler project — 16 agents over 2,000 sessions across two weeks — consumed approximately 2 billion input tokens and 140 million output tokens. Key takeaways:
  • Write extremely high-quality tests — agents solve whatever the verifier validates
  • Minimize verbose output — context pollution degrades performance
  • Maintain README/progress files so each fresh agent gets orientation context quickly
  • The constraint is always review bandwidth, not compute
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