Opus 4.6 vs Sonnet 4.6: Stop Defaulting to the Expensive One

Most teams default to Opus out of habit. With Claude 4.6, that habit costs you 5x on input and 5x on output for tasks Sonnet now handles just as well — sometimes better.

Here’s the honest framework.

Context: What Actually Changed in Claude 4.6

Both Opus 4.6 and Sonnet 4.6 ship with a 1M token context window — no beta headers, no special flags, just standard API access. That removes one of the oldest reasons to reach for Opus: the context advantage is gone.

The pricing delta hasn’t budged, though. Opus runs $15/M input, $75/M output. Sonnet is $3/M input, $15/M output. Haiku 4.5 sits at the bottom at $0.80/$4 if you need routing-tier economics.

What has changed is Sonnet’s ceiling. The 4.6 release brought major improvements to Sonnet’s coding abilities and dramatically better computer use performance. If you evaluated Sonnet 4.5 for your coding pipeline and walked away disappointed, the calculus has shifted. The gap between Sonnet 4.6 and Opus 4.6 on code generation tasks is much narrower than the previous generation — and on some benchmarks, Sonnet 4.6 is the preferred model outright.

Opus still wins on raw reasoning depth. It has 128k max output tokens versus Sonnet’s 64k, and it hits harder on multi-step planning, research synthesis, and tasks that require holding complex constraint graphs in working memory. But “harder” is doing a lot of work in that sentence — harder by how much, for what price?

Analysis: Where Each Model Actually Earns Its Place

Use Sonnet 4.6 for:

Code generation and review. This is the headline improvement. Sonnet 4.6 closes the gap on Opus for most practical coding tasks — refactoring, test generation, PR review, bug diagnosis. If you’re running a coding agent at volume, the math is brutal: a pipeline doing 10M output tokens/month drops from $750 to $150 by switching from Opus to Sonnet. That’s not a rounding error.

Tool use and agentic loops. Sonnet 4.6 is faster and cheaper in multi-turn tool-use pipelines, and the quality delta versus Opus in this category is small. Web search, web fetch, computer use — all improved significantly in Sonnet 4.6, and dynamic filtering support on web tools is available to both models equally.

High-throughput tasks. Anything running at scale — summarization, extraction, classification with some reasoning — belongs on Sonnet or Haiku, not Opus. Opus at high throughput is a budget problem waiting to happen.

Computer use. Sonnet 4.6’s computer use skills received a major upgrade. Unless your automation involves genuinely complex multi-step reasoning about UI state, Sonnet 4.6 is the right pick here, both economically and practically.

Use Opus 4.6 for:

Deep reasoning with long output. The 128k output limit matters when you need a model to produce extended structured analysis — long-form synthesis, comprehensive architectural documents, multi-chapter research outputs. Sonnet’s 64k ceiling can become a real constraint.

Multi-step planning with complex dependencies. When a task requires the model to hold a large constraint graph, reason through many interdependencies, and make coherent decisions across dozens of steps, Opus’s reasoning advantage compounds. Think: strategy synthesis across disparate sources, adversarial analysis, or long-horizon agent planning where mistakes early cascade badly.

Research synthesis. If you’re feeding Opus a 400k-token corpus of documents and asking for a structured synthesis with nuanced conclusions, you want Opus. The quality of reasoning over dense, contradictory material is where the price premium is most justified.

One-shot high-stakes tasks. If the cost of an error is significant and the task only runs once (or rarely), the price difference becomes irrelevant. Use the best model.

Adaptive Thinking: Use It on Both

Both models support thinking: { type: "adaptive" }. Turn it on by default — it lets the model decide when extended thinking is worth the overhead rather than forcing it on every turn. This is especially important on Opus where extended thinking adds cost on top of an already expensive base rate.

const response = await client.messages.create({
  model: "claude-opus-4-6-20260301", // or claude-sonnet-4-6-20260301
  max_tokens: 16000,
  thinking: {
    type: "adaptive",
    budget_tokens: 10000
  },
  messages: [{ role: "user", content: prompt }]
});


For Opus specifically: Fast Mode gives you 2.5x output speed at a premium price. If you have latency-sensitive Opus use cases, it's worth benchmarking — faster Opus is still expensive Opus, but it changes the equation for certain real-time applications.

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## Implications: A Decision Framework You Can Actually Use

Stop asking "which model is better?" and start asking "what does this task require?"

**Routing heuristic:**

| Task type | Model |
|---|---|
| Complex reasoning, multi-step planning | Opus 4.6 |
| Research synthesis over large corpora | Opus 4.6 |
| Code generation, review, debugging | Sonnet 4.6 |
| Agentic tool use, computer use | Sonnet 4.6 |
| High-throughput structured output | Sonnet 4.6 |
| Classification, routing, extraction | Haiku 4.5 |

**Budget reality check:** At $75/M output tokens, Opus is priced for tasks where it demonstrably outperforms alternatives. If you can't articulate why Sonnet won't work for your specific use case, you're probably paying the Opus tax unnecessarily.

**The volume trap:** Teams often prototype with Opus, observe good results, and ship to production without re-testing on Sonnet. Re-evaluate. What felt like a quality gap during prototyping may have closed — and Sonnet 4.6's coding improvements in particular mean many pipelines that were Opus-only are now Sonnet candidates.

**Haiku's role hasn't changed:** For pure routing, classification, or lightweight extraction at scale, Haiku 4.5 at $0.80/M input is still the right answer. Don't pull Sonnet into jobs Haiku handles cleanly.

The verdict: **default to Sonnet 4.6, graduate to Opus only when you can name the specific capability gap you're buying.** The 4.6 generation has made Sonnet genuinely competitive on coding and tool use, and the 1M context parity removes the last blanket reason to prefer Opus by default. Pay for Opus when you need Opus-tier reasoning. Don't pay for it on tasks that Sonnet handles fine.