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Claude Haiku vs Sonnet vs Opus: Pick Your Default

Picking a Claude model is a routing decision, not a loyalty test. For most developer workflows, start with Sonnet, move repetitive work to Haiku, and reserve Opus for problems where better reasoning could prevent expensive mistakes. Then validate that split against your actual tasks.

This quick-start guide explains how to choose, connect your tools, and measure whether a more expensive model earns its place.

1. Match the model family to the work

• Haiku: start here for bounded, high-volume tasks. Try classification, extracting fields from short documents, routing support tickets, and generating straightforward boilerplate. Give it a clear schema and explicit acceptance criteria. Low per-request cost matters when a feature runs thousands of times daily.
• Sonnet: the practical default for development. Use it for implementing features, debugging ordinary failures, reviewing pull requests, and explaining unfamiliar code. It generally occupies the middle ground between capability, latency, and cost.
• Opus: escalate difficult or ambiguous work. Test it on cross-module debugging, complex refactors, architecture trade-offs, and reasoning-heavy analysis. Its value is not longer answers; it is whether it solves cases that cheaper models miss.

These are family-level starting points, not permanent rankings. Compare exact model versions: a newer release can change the trade-off. Context windows, output limits, tool support, and pricing also vary by model ID.

2. Connect Claude Code through 59API

59API provides low-cost, pay-as-you-go access to Claude and GPT models, with compatibility for Claude Code, Codex, and OpenAI SDKs. Its stated offering uses native, official-quality models without downgrading, making it a practical option for testing multiple capability tiers without committing to a subscription.

• Create an API key: obtain a 59API key and check the dashboard for currently available Claude model IDs and prices.
• Set the endpoint: for Claude Code, set the environment variable ANTHROPIC_BASE_URL to https://api.59api.com.
• Configure authentication: set ANTHROPIC_AUTH_TOKEN to your 59API key using your shell or secret manager. Avoid committing credentials or putting them in shared project files.
• Select the model: set ANTHROPIC_MODEL to the exact supported model ID from 59API, then launch Claude Code with the claude command.
• Run a smoke test: ask it to explain one small source file. Check the selected model, successful response, and recorded usage before starting a large repository task.

If you use an OpenAI SDK instead, configure its API key and base_url according to 59API’s compatibility instructions. The service base is https://api.59api.com; use the documented versioned path if your SDK integration requires one rather than guessing endpoint suffixes.

3. Run a small benchmark before choosing

Collect 20 representative tasks: ten routine cases, five moderately difficult cases, and five previous failures. Remove sensitive data unless your provider agreement and organizational policy permit sending it.

Run every candidate with the same prompt, inputs, tools, and output budget. For coding, score passing tests and correctness, not how convincing the explanation sounds. For extraction, validate required fields and schema compliance.

• Quality: record accepted outputs divided by total tasks.
• Speed: measure end-to-end latency, including tool calls and retries.
• Cost: divide total spend by accepted outputs to calculate cost per successful task.

Check input, output, caching, and any applicable reasoning-token charges separately. A cheap request that needs three retries may cost more than one successful Sonnet response.

4. Ship a simple escalation policy

Route structured, easily validated work to Haiku. Use Sonnet for general coding. Escalate to Opus when tests still fail, requirements conflict, or the task needs deeper investigation. Preserve the original requirements and relevant failure evidence when escalating; do not pass along an unverified summary alone.

Keep validation in place at every tier. No model family replaces tests, authorization checks, or human review for consequential changes.

59API’s pay-as-you-go pricing makes this mixed-model approach accessible, and its referral rebate can further offset usage costs under the current program terms. Sign up for 59API when you are ready to benchmark your own workload, then let measured results—not model prestige—choose your default.

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