Claude Opus 5.5 vs Claude Sonnet 5.5: what the price difference buys
Sonnet is cheaper for the same uncached input and output. Cache reads tie, so high prompt reuse narrows the total gap without removing Opus's higher output cost.
Opus doubles the base input and output rates, while cache reads cost the same on both.
Claude Opus 5.5 charges twice Claude Sonnet 5.5's base input and output rates. The cache-read price is an exception: both charge $0.20 per million tokens read from cache. That makes a shared-context workflow different from a series of unrelated prompts. The right question is how much uncached input and output your application pays for, and whether using Opus improves the completed result enough to cover those higher rates.
By TechCompare · Updated
Cost Comparison
Based on 100,000 input tokens (50% cached), 5,000 output tokens, and 100 requests.Prices are fetched live from OpenRouter and may include temporary promotional discounts not accounted for in our article and comparison figures.
Side-by-side specs
| Spec | Claude Opus 5.5 | Claude Sonnet 5.5 |
|---|---|---|
| Standard input per 1M tokens | $4.00 | $2.00 (better on this spec) |
| Standard output per 1M tokens | $20.00 | $10.00 (better on this spec) |
| Cache reads per 1M tokens | $0.20 | $0.20 |
| 5-minute cache writes per 1M tokens | $5.00 | $2.50 (better on this spec) |
| 1-hour cache writes per 1M tokens | $8.00 | $4.00 (better on this spec) |
| 100K input + 5K output, no cache hits | $0.50 | $0.25 (better on this spec) |
| 100K input + 5K output, 50% cached input | $0.31 | $0.16 (better on this spec) |
| 100K input + 5K output, all input cached | $0.12 | $0.07 (better on this spec) |
| Context window | 1,000,000 tokens | 1,000,000 tokens |
| Provider Batch API discount | 50% | 50% |
How they differ
Opus costs $4 input and $20 output per million tokens, compared with Sonnet's $2 and $10. A 100,000-input, 5,000-output request without cache hits costs $0.50 on Opus and $0.25 on Sonnet. With half the input read from cache, the estimates become $0.31 and $0.16. If all 100,000 input tokens are eligible cache reads, they become $0.12 and $0.07. The gap narrows because cached input costs the same, but output remains twice as expensive on Opus. Five-minute cache writes cost $5 per million on Opus and $2.50 on Sonnet, with one-hour writes at $8 and $4. Both support a 1M context window at standard rates and a 50% provider Batch API discount. These worked estimates exclude writes and tool fees. The embedded chart uses live OpenRouter prices and can differ with provider routing.
Verdict
Use Sonnet as a candidate for tasks it completes to your required standard, then evaluate Opus on the work that remains difficult. An agent with frequent cache hits can make Opus less than twice as expensive per call, but that doesn't automatically make it better value. Track the number of attempts, output tokens, and human corrections per successful task. Route using those measurements rather than treating the Opus name as evidence of a benefit on every workload.
Which should you pick?
Choose Claude Opus 5.5
Use Opus when your evaluation shows a worthwhile improvement on longer agent workflows, coding tasks, or document analysis. A reused cache can reduce the cost of repeated context, but creating and refreshing that cache still costs money. Set budgets for reasoning and tool turns so a small quality gain doesn't arrive with an unexpectedly large output bill.
Choose Claude Sonnet 5.5
Use Sonnet when it reaches the same success criteria with acceptable response times and review effort. Its lower uncached-input, output, and write rates matter for one-off requests, growing conversations, and output-heavy applications. Keep an escalation path for tasks that need another attempt on Opus instead of paying the higher rate for every routine request.