Claude Opus 5.5 vs. Opus 5 on reasoning tasks: Cheaper, faster, but not better

claude opus 5 5 vs opus 5

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Author: Pixwit Team · Date: October 15, 2026

Claude Opus 5.5 vs. Opus 5 on reasoning tasks: Cheaper, faster, but not better

When Anthropic [released Claude Opus 5.5]( developer publication.io/claude-opus-5-5-release/) this week, the company claimed the new model costs 40% less than Opus 5 and generates output 30% faster. Anthropic’s marketing makes three claims. Opus 5.5 performs at the level of [Claude Fable 5.1]( developer publication.io/anthropic-fable-5-1-launch/) (so it should outperform Opus 5), costs 40% less than Opus 5 on typical workloads, and generates output more than 30% faster. Anthropic also cut the price developers pay to use the model through its API. Opus 5.5 costs $4 for every million tokens (chunks of text roughly three-quarters of a word long) sent to the model and $20 for every million it writes back, down from $5 and $25 for Opus 5. That price cut alone accounts for a 20% saving. The rest of the claimed 40% saving has to come from the model using fewer tokens. I wanted to see how this translates for the average Claude user, so I skipped the usual developer workflow simulations this time. Lately, the models I test [handle everyday tasks well]( developer publication.io/claude-fable-upgrade-tested/). Reasoning tasks are where I’ve seen them struggle, so I tested Opus 5 against Opus 5.5 on reasoning tasks only. You can find the prompts at the bottom of this post if you want to replicate these tests on your own system.

The tests

I called both models through the Anthropic API with identical prompts. Both ran with adaptive thinking at the default effort level, since Opus 5.5 doesn’t allow you to turn thinking off. Each problem ran once per model. I planned to rerun any problem where the models gave me different results, but they never did. Here are the tests I ran:

Logic grid (medium difficulty) – Seven engineers each have an on-call day, a language, a service, and a city, and 22 clues pin down one answer. Six clues are conditional or “exactly one of these is true” statements, and removing any single clue breaks the puzzle.
Constrained orderings (hard difficulty) – Reorder 10 deploy jobs so no job stays in its original slot and no two consecutively numbered jobs sit side by side. The model had to give the count for 6, 8, and 10 jobs.
Stone game with memory (harder difficulty) – Players remove 2, 5, 7, or 11 stones, but can’t repeat their opponent’s last move or their own. The model had to find who wins from 200 stones, count the losing starting sizes up to 500, and name the smallest losing size above 340. I logged input tokens, output tokens, cost at list price, and time for every call. Thinking tokens are billed as output, so I included them.

The logic grid

Both models got all 28 cells right. Opus 5.5 took 65 seconds and 7,573 output tokens, for $0.16. Opus 5 took 108 seconds and 10,621 output tokens, for $0.27. On this test, Opus 5.5 was 43% cheaper and delivered the same correct answer. Opus 5.5 was slightly more detailed and noted that it didn’t fully prove the solution was unique.

Constrained orderings

Neither model produced an answer, which made this the hardest problem in practice. The correct counts are 27, 1,695, and 159,019. The third answer is very hard to reach by reasoning alone. A computer program that checks every possible ordering can find it, but neither model could run code in this test. With a 48,000-token output limit, both models spent the whole budget thinking and never replied. Opus 5.5 used 489 seconds and $0.96. Opus 5 used 553 seconds and $1.20. I raised the limit to 128,000 tokens and ran it again. Opus 5 used every token, took over 25 minutes, and stopped with no answer. That cost $3.20. Opus 5.5 ran for 19 minutes and used 112,733 tokens, but the API ended the response with a “refusal” stop reason and no text. The prompt asks the model to count job orderings and contains nothing sensitive. That means the refusal was most likely a mistake by Anthropic’s safety filter flagging a harmless request. Opus 5.5 was cheaper, but how much does that matter if you don’t get a result?

The stone game

And we’re back to the same answers again. Both models answered all three parts correctly. The first player loses from 200 stones; starting sizes from 120 to 500 are losses, and the smallest loss above 340 is 344. The difference in this test came down to how much thinking each needed to get there. Opus 5.5 finished in 215 seconds with 28,740 output tokens, costing $0.58. Opus 5 took 624 seconds and produced 74,981 output tokens, costing $1.88. Opus 5.5 used 62% fewer tokens and cost 69% less for the same answer.

Results

What do I think

Anthropic’s benchmarks show Opus 5.5 ahead of Opus 5 on coding, knowledge work, and reasoning. I didn’t rerun those benchmarks. I gave both models the same three reasoning problems, and they performed equally. Both solved the logic grid and the stone game, and both failed the ordering problem. The savings are real. Opus 5.5 cost less and finished sooner on every problem, including 43% less on the logic grid and 69% less on the stone game. Most of that came from using fewer output tokens. The price cut accounts for 20%. Its writing speed was 11% faster, short of the 30% Anthropic claims. Switch to Opus 5.5 if you run Opus 5 today. You get the same results on hard reasoning for less money and less waiting. Set a hard output limit and watch your spend on hard problems, though. Both models can think for close to 20 minutes or more and return nothing, which is a problem if you pay for every token. For counting problems like the ordering test, give the model a code execution tool instead of hoping it reasons its way through.

The prompts

Logic grid Seven engineers (Ana, Ben, Cy, Dee, Eli, Fay, Gus) share an on-call rotation. Each is on call on exactly one day of a single week, Monday through Sunday (Monday is the earliest day, Sunday the latest), and no two share a day. Each writes a different language (Go, Rust, Python, Java, Kotlin, TypeScript, C++), owns a different service (auth, billing, search, queue, cache, gateway, metrics), and is based in a different city (Berlin, Tokyo, Denver, Lagos, Sydney, Toronto, Mumbai). Clues: The Java developer is Gus. The TypeScript developer is on call exactly two days after the queue owner. Exactly one of these is true: the engineer based in Berlin owns billing, or the C++ developer is on call Monday. Exactly one of these is true: the engineer based in Tokyo owns cache, or the engineer based in Tokyo writes Rust. If Fay is on call Sunday, then the engineer based in Denver does not write Kotlin. Exactly one of these is true: the Kotlin developer owns auth, or the C++ developer is Cy. The engineer based in Tokyo is on call earlier in the week than the C++ developer. The engineer based in Denver does not write Python. Exactly one of these is true: the Go developer is Ben, or the gateway owner is based in Berlin. Ana is based in Mumbai. The TypeScript developer is on call earlier in the week than Fay. The engineer based in Sydney is on call earlier in the week than the billing owner. The gateway owner is on call earlier in the week than the Kotlin developer. The engineer on call Sunday is not based in Berlin. Fay and the engineer based in Lagos are on call on consecutive days. Eli is on call exactly three days after the auth owner. The engineer based in Lagos writes Java. Exactly one of these is true: the search owner is Eli, or the cache owner is Dee. The gateway owner and the Go developer are on call on consecutive days. The engineer based in Lagos is on call exactly four days after the auth owner. The engineer based in Lagos owns metrics. The engineer based in Mumbai is on call earlier in the week than the Python developer. Determine the full assignment. At the end of your response, give exactly seven lines, one per engineer in the order Ana, Ben, Cy, Dee, Eli, Fay, Gus, in this format: ANSWER: Name | Day | Language | Service | City

Ordering problem

A build system has n deploy jobs numbered 1 to n. Originally, job k runs in slot k. You reorder all n jobs into slots 1 to n (each slot gets one job) subject to two rules: No job runs in its original slot (job k is not in slot k). Jobs with consecutive numbers never run in adjacent slots (for example, jobs 4 and 5 cannot be in slots i and i+1 in either order). How many valid orderings are there for (a) n = 6, (b) n = 8, (c) n = 10? At the end of your response, give exactly three lines in this format: ANSWER a: <number> ANSWER b: <number> ANSWER c: <number> Stone game Two players play a game with a pile of stones. They alternate turns. On each turn, a player removes exactly 2, 5, 7, or 11 stones, subject to two rules: You may not remove the same number your opponent removed on their most recent turn. You may not remove the same number you removed on your own most recent turn. (On the very first turn of the game, neither rule applies. On the second player’s first turn, only the first rule applies.) You cannot remove more stones than are in the pile. A player who has no legal move on their turn loses. Both players play perfectly. (a) Starting with 200 stones, does the first player win? (b) For how many starting pile sizes from 1 to 500 inclusive does the first player lose? (c) What is the smallest starting pile size greater than 340 for which the first player loses? At the end of your response, give exactly three lines in this format: ANSWER a: <yes or no> ANSWER b: <number> ANSWER c: <number> [YOUTUBE.COM/a developer publication channel to stream all our podcasts, interviews, demos, and more.]( developer publication?sub_confirmation=1)

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Claude Opus 5.5 vs. Opus 5 on reasoning tasks: Cheaper, faster, but not better