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opus 5 vs opus 5.5
Opus 5 vs Opus 5.5 on three hard reasoning tasks: identical answers, 43%–69% lower cost, and about 11% faster output from the same API prompts.
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Why Compare Opus 5 vs Opus 5.5
Anthropic promises Opus 5.5 is cheaper and faster than Opus 5. These tests check whether the cost and speed gains hold up on real reasoning work.
- Anthropic's Cost and Speed ClaimsThe pitch is a 40% lower bill, more than 30% faster output, and reasoning that matches Claude Fable 5.1 rather than trailing Opus 5.
- API Pricing ChangesOpus 5.5 bills $4 for each million input tokens and $20 for each million it writes back, down from $5 and $25 — a change worth a 20% saving on its own.
- Reasoning Task Testing MethodIdentical prompts went to both models through the Anthropic API with adaptive thinking at default effort, one run per problem per model.
How the Opus 5 vs Opus 5.5 Tests Were Run
Three hard reasoning problems, one run per model, with tokens, time, and list-price cost logged on every call.
Opus 5 vs Opus 5.5 Results at a Glance
Cost, token use, writing speed, and failure modes measured across the Opus 5 vs Opus 5.5 reasoning runs.
Logic Grid Accuracy
Every one of the 28 grid cells came out right for both models; Opus 5.5 added a note that it had not fully proven the answer was the only one.
Token Efficiency
Opus 5.5 wrote 62% fewer output tokens on the stone game and cost 43% less on the logic grid, largely by writing less.
Output Speed
Across all calls Opus 5.5 wrote 103.4 tokens per second against Opus 5's 93.1, about 11% faster, with a 19% best single-problem lead.
Cost Per Problem
Opus 5.5 cost $0.16 versus $0.27 on the logic grid and $0.58 versus $1.88 on the stone game, with total test spend of $10.50.
Hard Problem Failures
The ordering puzzle defeated both models: each can burn roughly 20 minutes of thinking and reply with nothing, and Opus 5.5 closed on a refusal stop reason.
Code Execution Tool Recommendation
When a task is really about counting — the ordering test included — hand the model a code execution tool rather than trusting it to reason to the number.
Opus 5 vs Opus 5.5 — FAQ
Common questions about Opus 5 vs Opus 5.5 pricing, output speed, and reasoning results.
Is Opus 5.5 cheaper than Opus 5?
Yes. It came in 43% cheaper on the logic grid and 69% cheaper on the stone game, mostly because it wrote fewer output tokens.
Is Opus 5.5 faster than Opus 5?
Yes, roughly 11% faster overall, with its widest single-problem margin at 19% — still short of the 30% Anthropic advertises.
Does Opus 5.5 reason better?
No. On the three problems the two models were indistinguishable: each handled the logic grid and the stone game, and each came up empty on the constrained orderings puzzle.
Why did Opus 5.5 refuse a harmless prompt?
On the ordering test it closed with a refusal stop reason and no text, most likely a safety filter mistake flagging a harmless request.
Should I switch to Opus 5.5?
If you run Opus 5 today, yes: the hard-reasoning answers stay the same while the bill and the wait shrink — just set a hard output limit first.
How do I control costs on hard problems?
Set a hard ceiling on output and track spend, since either model may spend around 20 minutes thinking and hand back nothing while tokens still bill.
Rerun the Opus 5 vs Opus 5.5 Tests Yourself
Copy the published prompts, run both models on your own system, and move to Opus 5.5 with a hard output limit to bank the cost and speed gains.