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opus 5 vs opus 5.5
We tested Opus 5 vs Opus 5.5 on three brutal reasoning problems — identical accuracy, 43–69% lower bills, and ~11% faster streaming.
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Opus 5 vs Opus 5.5: What Our Tests Reveal
Anthropic markets Opus 5.5 as the cheaper, quicker successor to Opus 5. We put those claims to work on genuine hard-reasoning prompts.
- The Vendor's Pricing and Speed PromisesThe pitch is a 40% smaller bill, over 30% faster writing, and reasoning on par with Claude Fable 5.1 instead of trailing Opus 5.
- Per-Million Token RatesOpus 5.5 charges $4 per million input tokens and $20 per million generated, versus $5 and $25 before — already a 20% reduction by itself.
- How We Ran the Reasoning TasksBoth models received the same prompts via the Anthropic API, adaptive thinking at default effort, a single run per problem each.
How We Benchmarked Opus 5 vs Opus 5.5
Three tough reasoning challenges, a single run per model, logging tokens, elapsed time, and list-price cost on each call.
Opus 5 vs Opus 5.5: The Scorecard
Spend, token volume, writing speed, and failure patterns captured across every Opus 5 and Opus 5.5 reasoning run.
Grid Puzzle Accuracy
All 28 cells landed correctly for both systems, though Opus 5.5 flagged that it had not fully proven its solution was unique.
Token Economy
On the stone game Opus 5.5 emitted 62% fewer output tokens, and on the grid it cost 43% less — mostly by writing more concisely.
Streaming Speed
Averaged over every call, Opus 5.5 streamed 103.4 tokens per second versus 93.1 for Opus 5 — roughly 11% quicker, peaking at a 19% lead on one problem.
Spend Per Problem
The logic grid ran $0.16 against $0.27, and the stone game $0.58 against $1.88, bringing the whole test to $10.50.
Where Both Models Fail
Neither model cracked the ordering puzzle: each could spend about 20 minutes thinking and return nothing, with Opus 5.5 ending on a refusal stop reason.
Use a Code Execution Tool
If a problem is fundamentally about counting, the ordering test included, give the model a code execution tool instead of trusting pure reasoning.
Opus 5 vs Opus 5.5: Questions Answered
Answers on Opus 5 vs Opus 5.5 pricing, streaming speed, refusal behavior, and reasoning accuracy.
Does Opus 5.5 cost less than Opus 5?
It does. Spend dropped 43% on the logic grid and 69% on the stone game, mainly because fewer output tokens were generated.
Does Opus 5.5 stream output faster?
About 11% quicker across the board, topping out at a 19% edge on one problem — below the 30% figure Anthropic advertises.
Is Opus 5.5 smarter at reasoning?
Not on these tests. The pair performed identically: both solved the logic grid and stone game, and both failed the constrained ordering puzzle.
Why did Opus 5.5 reject a harmless request?
The ordering run ended with a refusal stop reason and no output — most likely a safety filter misfiring on an innocent prompt.
Is it worth moving to Opus 5.5?
For current Opus 5 users, yes: reasoning quality holds while cost and latency fall — just cap output tokens before you start.
How can I keep costs down on hard tasks?
Cap output length and monitor usage, because either model can think for roughly 20 minutes, return nothing, and still bill for every token.
Run Your Own Opus 5 vs Opus 5.5 Comparison
Grab the same prompts, benchmark both models on your stack, and adopt Opus 5.5 with a strict output cap to lock in the savings.