Which is better for a high-volume coding pipeline: Sonnet 5 or Opus 5?

For this specific workload shape - many requests, individually well-defined and bounded in scope, like routine bug fixes, test generation, or standard refactors - Sonnet 5 is generally the better fit, since its lower per-token cost compounds meaningfully at high request volume, and reporting suggests it handles this category of task well, in some cases matching or slightly exceeding Opus 4.8 on specific coding benchmarks.

Opus 5's advantage is concentrated in a different task shape: complex, open-ended, or long-horizon work where deeper reasoning materially changes the outcome - for a pipeline made up of many individually well-scoped tasks, that advantage is less likely to be the deciding factor on most individual requests, even though it would matter more on the harder subset.

The recommended pattern for exactly this situation is a tiered pipeline rather than a single-model choice: run Sonnet 5 as the default across the high-volume pipeline, and add automatic or manual escalation to Opus 5 specifically for the subset of requests that fail, need multiple retries, or are flagged as unusually complex - capturing Sonnet 5's cost efficiency across the bulk of volume while still reaching for Opus 5's deeper capability exactly where it's actually needed.

Effort tuning on the Sonnet 5 side of this pipeline is also worth optimizing specifically, since a well-scoped, high-volume pipeline is exactly the situation where testing medium effort before defaulting to high can meaningfully reduce cost across the full volume without necessarily costing much in output quality for tasks that were already well within Sonnet 5's comfortable capability range.