Answer first: use Claude Sonnet 5 as the first candidate for routine, high-volume agent work; escalate to Claude Opus 5 for difficult debugging, ambiguous planning, long-horizon changes, or knowledge work where a failure is costly. The right default comes from a matched acceptance test, not a universal leaderboard.
Provider roles and published prices
| Decision | Claude Sonnet 5 | Claude Opus 5 |
|---|---|---|
| Starting role | Everyday agentic planning, tools, coding, and knowledge work | Harder everyday work closer to Anthropic’s frontier tier |
| API ID | claude-sonnet-5 | claude-opus-5 |
| Published API price | $2 input / $10 output per million tokens through August 31, 2026; then $3 / $15 | $5 input / $25 output per million tokens at launch |
| Fast mode | Check current provider docs | About 2.5× default speed at twice Opus 5’s base price |
| Best first pilot | High-volume, cost-sensitive, bounded work | Hard, ambiguous, long-running, or review-expensive work |
Pricing, access, and product limits can change. Verify the live Claude Platform and plan surfaces before procurement.
Use Sonnet 5 for the routine band
Start with Claude Sonnet 5 when tasks:
- have clear acceptance tests and bounded scope;
- repeat at high volume;
- can escalate uncertain results;
- are sensitive to token cost;
- do not need the strongest available Opus reasoning on every request.
Examples include first-pass issue triage, narrow refactors, test generation, document extraction, and standard research synthesis—provided the application validates the result.
Use Opus 5 where the failure floor matters
Start with Claude Opus 5 when tasks:
- require root-cause analysis across an unfamiliar codebase;
- mix planning, tools, implementation, testing, and self-correction;
- contain ambiguous requirements that need explicit judgment;
- involve long documents or several interdependent artifacts;
- consume substantial reviewer time when the first result is wrong.
The higher provider rate can be rational when fewer retries, shorter investigations, or fewer escaped defects reduce the complete cost.
Build an enterprise acceptance set
Use real, permission-safe examples from four bands:
- Routine: narrow change with deterministic tests.
- Complex: multi-file implementation with incomplete information.
- Adversarial: misleading instruction, unsafe request, or prompt injection in tool data.
- Operational: timeout, tool error, partial result, and human handoff.
Keep the prompt, tools, permissions, repository state, and acceptance rules identical. Run enough repeats to expose variance.
Measure:
- pass rate and severe defect rate;
- tool calls, retries, and tokens;
- p50 and p95 latency;
- reviewer minutes and corrections;
- unauthorized or unnecessary changes;
- recovery from tool and policy failures.
Route by difficulty if the result is mixed. A practical system can default to Sonnet 5 and escalate to Opus 5 when risk, uncertainty, or a failed validation justifies it.
Keep model, plan, and Flowith access separate
Anthropic consumer-plan availability does not establish API entitlement, and Anthropic provider availability does not establish Flowith availability. Check the relevant live product surface for each decision.
For implementation changes, use the Opus 5 API migration and fallback guide.
FAQ
Should I use Claude Opus 5 or Sonnet 5 for coding?
Start with Sonnet 5 for routine, high-volume work and Opus 5 for harder debugging, ambiguous implementation, long-horizon changes, or tasks where review failures are expensive. Confirm with a matched repository test.
Which model has the lower API price?
Sonnet 5 has the lower published rate. Its standard rate is $3 input and $15 output per million tokens after an introductory window, while Opus 5 launched at $5 input and $25 output.
When can Opus 5 be cheaper overall?
When its higher task success, fewer retries, shorter tool loops, or lower human review effort outweigh the higher token rate. Measure accepted-task cost rather than price alone.
Does this guide confirm either model in Flowith?
No. Provider availability and Flowith availability are separate. Check the live Flowith workspace model selector.
Official sources
Sources checked July 29, 2026: