Short answer: Use Sonnet for the bulk of agentic coding — editing, refactoring, test-writing, routine multi-step tasks — because it is fast and far cheaper. Reach for Opus on genuinely hard reasoning: tricky architecture, gnarly debugging, or long-horizon planning. The cost gap is large, so defaulting to Sonnet and escalating to Opus deliberately is the sweet spot.
The trade-off in one line
Opus reasons more deeply; Sonnet is faster and costs several times less per token. On a long agentic run the model choice dominates both your bill and your rate-limit burn.
When Sonnet is the right call
- Applying a known change across many files
- Writing tests, docs, and boilerplate
- Routine refactors and mechanical edits
- High-volume agentic steps where speed and cost matter more than peak reasoning
When Opus earns its price
- Architecture and design decisions with many trade-offs
- Hard, multi-layer debugging where a wrong guess is expensive
- Long-horizon planning that has to hold a lot of context coherently
The cost + rate-limit angle
Because Opus consumes quota faster and costs more, running it as your default both inflates spend and burns your 5-hour and weekly windows quickly. Defaulting to Sonnet stretches every limit; escalating to Opus only when needed keeps quality where it counts.
How Power Claude helps you tune this
Power Claude tracks per-model $/token usage locally, so you can see exactly how much Opus is costing on a given session and whether the result justified it. Paired with multi-account pooling, even Opus-heavy work runs without stalling on a single account’s limits. Local, free for 7 days, no card.
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Frequently asked questions
Should I use Opus or Sonnet for coding?
Use Sonnet for most coding — it is fast and much cheaper — and switch to Opus for hard reasoning, architecture, or tough debugging. Defaulting to Sonnet and escalating deliberately gives the best cost/quality balance.
Is Opus worth the extra cost for agentic coding?
On genuinely hard problems, yes; on routine multi-step work, usually not. Track per-model cost so you can tell which sessions Opus actually improved.
Does using Opus hit rate limits faster?
Yes — Opus consumes quota faster, so heavy Opus use reaches the 5-hour and weekly caps sooner. Pooling accounts (e.g. with Power Claude) offsets this by spreading load across independent windows.
Can I switch models mid-session?
Yes, Claude Code lets you change the model during a session — a practical pattern is Sonnet by default, Opus for the few steps that need it.