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News · Anthropic · September 28, 2026

Published . By , AI-assisted.

Claude Sonnet 5.5 is out: what changed, and what it costs you

Update, October 7, 2026: Cache-read price halved: $0.10 per million. Anthropic released Claude Sonnet 5.5 on September 28, 2026, at $2 per million input tokens and $10 per million output tokens, the same price as Sonnet 5. Claude Sonnet 5.5 has been in llmwise since September 28, 2026: up to 125 Claude Sonnet 5.5 messages a month on Pro ($20).

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Facts checked against Anthropic: Introducing Claude Sonnet 5.5, Anthropic: Introducing Claude Haiku 5.5, Claude Platform Docs: Models overview, Claude Platform Docs: Pricing, Claude Platform Docs: What's new in Claude Sonnet 5.5. Updated .

Update, October 7, 2026

What changed on October 7, 2026, from Anthropic's own pages; the story as first published follows below, as it was.

  1. Cache-read price halved: $0.10 per million.[2][4]

  2. Anthropic cut Sonnet 5.5's cache reads from $0.20 to $0.10 per million tokens, 5% of its input price; its input, output and cache-write prices didn't change.[2][4]

What Anthropic announced

Each point is from Anthropic's own announcement unless its source says otherwise; the numbers link to the sources below.

  1. Anthropic calls Sonnet 5.5 the second model in the Claude 5.5 family, and a faster, lower-cost complement to Claude Opus 5.5.[1]

  2. Anthropic says Sonnet 5.5 writes its output more than 30% faster than Sonnet 5, and costs up to 30% less per task because it needs far fewer tokens for the same work.[1]

  3. At launch, cache reads cost $0.20 per million tokens and cache writes $2.50 per million, half of Opus 5.5's cache-write price.[1]

  4. Its context window is 1 million tokens, it can write up to 128,000 tokens in one reply, and its training data runs to June 2026.[3]

  5. On Terminal-Bench 4.0, an agentic coding test, Anthropic reports 70.6% for Sonnet 5.5, against 10.3% for Sonnet 5 and 66.4% for Opus 5.5.[1]

  6. Anthropic says Opus 5.5 remains clearly stronger at complex, open-ended work that needs sustained judgment.[1]

  7. It's the first Sonnet with safety classifiers that can decline a request; Anthropic retries its cyber and AI-development declines on Claude Sonnet 5.[5]

  8. It's on the Claude Platform as claude-sonnet-5-5, and through Amazon Web Services, Google Cloud and Microsoft Azure.[1]

  9. Anthropic says Claude Haiku 5.5 will join the Claude 5.5 family in the coming weeks.[1]

Can you use Claude Sonnet 5.5 in llmwise?

What Claude Sonnet 5.5 costs you in llmwise, from the plans themselves.

Claude Sonnet 5.5

Claude Sonnet 5.5 has been in llmwise since September 28, 2026. llmwise's catalog prices it at $2.00 per million tokens in and $10.00 out (Anthropic's list price). But a Claude Sonnet 5.5 message isn't billed by the token: the table below has its count on every plan.

Claude Sonnet 5.5 on every llmwise plan
PlanClaude Sonnet 5.5
Free ($0)Not in the trial
Plus ($10)Up to 62 a month, about $0.16 each
Pro ($20)Up to 125 a month, about $0.16 each
Max ($50)Up to 400 a month, about $0.13 each
Ultra ($100)Up to 900 a month, about $0.11 each
Studio ($200)Up to 2,000 a month, about $0.10 each

A paid plan's month is one allowance the models share. So a monthly count is the most you get if the month goes to that model, and “each” is the plan's price divided by it. Every message's price is shown before you send it. Every plan.

The counts above come with each plan's fair-use limit, in AI cost a month: Plus's is $3.75, Pro's $7.50, Max's $20, Ultra's $42, Studio's $85. That leaves room for every message at typical sizes, less if messages run very long or research-heavy. Every limit, explained.

How did Claude Sonnet 5.5 do on our test prompts?

Beside GPT-6.1 Sol and GPT-6 Sol, the models from other makers nearest in price per message.

Claude Sonnet 5.5 and the nearest-priced rivals: prompts passed
Prompt kindClaude Sonnet 5.5GPT-6.1 SolGPT-6 Sol
Writing4 of 54 of 54 of 5
Summarization4 of 55 of 54 of 5
Support replies4 of 52 of 53 of 5
Translation5 of 55 of 54 of 5
In total47 of 5046 of 5045 of 50

All passed every prompt on coding, math, data analysis, SQL, answering from documents, and tool use. Through OpenRouter, in our test runs of September 27, 28, 29 and October 2, 7, 8, 9, 15, 2026; every model got the same prompts. Read the replies.

Sources

  1. [1] Anthropic: Introducing Claude Sonnet 5.5, published .
  2. [2] Anthropic: Introducing Claude Haiku 5.5, published .
  3. [3] Claude Platform Docs: Models overview, checked .
  4. [4] Claude Platform Docs: Pricing, checked .
  5. [5] Claude Platform Docs: What's new in Claude Sonnet 5.5, checked .
Bar chart: Claude Sonnet 5.5 messages on each llmwise plan. Plus ($10): up to 62 a month; Pro ($20): up to 125 a month; Max ($50): up to 400 a month; Ultra ($100): up to 900 a month; Studio ($200): up to 2,000 a month.
llmwise's published counts, plan by plan.

Claude Sonnet 5.5: what it means for you

Can I use Claude Sonnet 5.5 in llmwise?

Yes, since September 28, 2026. Claude Sonnet 5.5's messages a month: up to 62 on Plus ($10), 125 on Pro ($20), 400 on Max ($50), 900 on Ultra ($100), 2,000 on Studio ($200). It isn't in the free trial.

Claude Sonnet 5.5 is in llmwise

Up to 125 Claude Sonnet 5.5 messages a month on Pro ($20). Its count shows before you send.

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