The Complete Claude Sonnet 5.5 Guide
Claude Sonnet 5.5 (model ID claude-sonnet-5-5) launched on 2026-09-28: a 1M context window and 128K maximum output, input $2 / output $10 per million tokens, cache reads at $0.20 — priced, the official post says, the same as Sonnet 5. Anthropic says it runs 30%+ faster than its predecessor and costs up to 30% less for most work. This page lays out the specs, pricing, default effort and the five breaking changes in one go.
Updated 2026-09-29
Four specs and defaults
Input / output (per million tokens)
Priced the same as Sonnet 5, per the official post. Sonnet 5's $2 / $10 is confirmed as the standard rate, and the increase to $3 / $15 once scheduled for 2026-09-01 will not happen.
Cache write 5-minute / 1-hour
Prices printed in the official list: $2.50 for a 5-minute cache write, $4 for a 1-hour write, $0.20 for cache reads; these are not converted into multipliers here.
Context window / max output
From the official model table: a 1M-token context and 128K-token maximum output, with a reliable knowledge cutoff of June 2026.
Default effort
The official line: Medium by default in Claude Code and the apps, High by default on the Claude Platform; you can set effort explicitly yourself.
Where it sits in the family
The official launch post calls Sonnet 5.5 the second model released in the Claude 5.5 family (the first was Opus 5.5, released 2026-09-22). The official wording on the division of labor is that complex work requiring careful judgment goes to Opus 5.5, while "well-scoped everyday tasks, fixing bugs, and creating polished documents, slides, and spreadsheets" are where it is strongest. Price is parity, not a selling point: the post says input $2, output $10 and cache reads at $0.20 cost the same as on Sonnet 5, and Batch is $1 / $5. Sonnet 5 is not being deprecated either — the official deprecation table marks both rows Active.
The vendor's own framing (released 2026-09-28)
The official launch post says Sonnet 5.5 "runs 30%+ faster, and costs up to 30% less for most work," and the cost section adds "In our testing, it costs up to 30% less per task than its predecessor" — both are Anthropic's own claims and self-testing, not third-party measurements. The Claude Code changelog for 2.1.284 marks claude-sonnet-5-5 as "now the default Sonnet model on the Anthropic API": that is the default this Claude Code client picks on the Anthropic API, not an API-wide default model. On the launch post the vendor still only says Haiku 5.5 will join the family in the coming weeks.
The Sonnet 5.5 timeline
Claude Opus 5.5 is released; the official Opus 5.5 page says Sonnet 5.5 and Haiku 5.5 will follow in the coming weeks.
Claude Sonnet 5.5 ships at the same price as Sonnet 5; from Claude Code 2.1.284 the default Sonnet becomes it.
The figures and quotes on this page were checked against the official pages on this date; as of 2026-09-29 you can use both claude-sonnet-5-5 and claude-sonnet-5 on QCode.
Confirmed vs not verified
Confirmed (verbatim in the official pages)
All of the following are officially confirmed and can be checked word for word in the official docs and price list: released 2026-09-28, model ID claude-sonnet-5-5, 1M / 128K, input $2 / output $10, cache reads $0.20, cache writes $2.50 and $4, Batch $1 / $5, priced the same as Sonnet 5, default effort (high on the platform, medium in Claude Code and the apps), five breaking changes, and the default-tier change in Claude Code 2.1.284. The speed, efficiency and score figures also come from the official pages, but those are the vendor's own claims and Anthropic's own testing. One further item is not a vendor statement but a measurement taken here on 2026-09-29: claude-sonnet-5-5 is available to call on QCode.
Unverified and not published by the vendor
Three things have not been verified, so don't plan around them: first, Haiku 5.5's pricing, context and model ID are not published by the vendor — only the single "coming weeks" line exists; second, the "30%+ faster" and "up to 30% less per task" figures are the vendor's own measurements, and this page has found no third-party replication; third, comparison figures and screenshots reportedly circulating online have no first-hand source, and this page does not carry them.
How it stacks up against Sonnet 5 and Opus 5.5
vs Sonnet 5
Input $2, output $10 and cache reads at $0.20 are priced the same as on Sonnet 5, per the official post — there is no price bump at all. The difference is efficiency and behavior: in Anthropic's own testing on Terminal-Bench 4.0, Sonnet 5.5 scores 70.6% and Sonnet 5 scores 10.3%, and the company says it runs 30%+ faster. What actually demands code changes is the five breaking changes.
vs Opus 5.5
The official line reserves Opus 5.5 for complex work that calls for careful judgment — a division of labor, not a ranking. Converted from the official price list: Sonnet 5.5 is exactly half of Opus 5.5 on input and output ($2 / $10 vs $4 / $20). Cache reads are the same $0.20 on both, and the price-list footnote bills Opus 5.5 cache hits and refreshes at 0.05x the base input price.
Five things to check when you switch over
The official docs state it plainly: "Five breaking changes affect code already running on Claude Sonnet 5": first, you can turn off up-front thinking with between_tools; second, forced tool use returns an error; third, thinking blocks are tied to the model and conversation that produced them; fourth, the Claude API and Google Cloud no longer accept the earlier computer_20251124 computer-use tool; fifth, the advisor tool rejects Claude Opus 4.8, Claude Opus 4.7 and Claude Sonnet 5 as advisors. One more change fails no request but alters the response shape: text between tool calls comes back inside thinking blocks.
On QCode
claude-sonnet-5-5 has been available on QCode since 2026-09-29 (official list $2 / $10, cache reads $0.20). To call it, copy a key in the console, use QCode's Anthropic-compatible endpoint, put claude-sonnet-5-5 in the model field and leave the rest as it is. The same key also runs claude-sonnet-5 ($2 / $10) and claude-opus-5-5 ($4 / $20): switching changes the model field only, same endpoint, same key.
Frequently asked questions
How is the claude-sonnet-5-5 ID written on each platform?
It is claude-sonnet-5-5 on the Claude API, Google Cloud, Microsoft Foundry and Claude Platform on AWS, and anthropic.claude-sonnet-5-5 on Amazon Bedrock. The Claude API alias in the official model table is also claude-sonnet-5-5, with no date suffix; the deprecation table marks it Active, with retirement no sooner than 2027-09-28.
How much does Sonnet 5.5 cost? Same as Sonnet 5?
The same. The Sonnet 5.5 row in the official price list reads: input $2, a 5-minute cache write $2.50, a 1-hour cache write $4, cache reads $0.20, output $10 per MTok; Batch is $1 / $5. The launch post states that input $2, output $10 and cache reads at $0.20 are priced the same as Sonnet 5. One more: Sonnet 5's scheduled 2026-09-01 increase to $3 / $15 will not occur, per the price-list footnote.
How much faster and cheaper is it than Sonnet 5?
The company says it "runs 30%+ faster," and that in its testing "it costs up to 30% less per task than its predecessor" — Anthropic's own claims. The official pages carry other self-tested scores, which this page does not transcribe; the Terminal-Bench 4.0 figures here, 70.6% vs 10.3%, are also Anthropic's own testing, with no third-party audit. Input, output and cache-read prices match Sonnet 5, so your saving depends only on your own token usage.
Do I need to change code when moving from Sonnet 5?
Possibly. The official list has five breaking changes (see the section above); the two easiest to hit are thinking-related: disabling thinking outright returns an error, and between_tools is accepted only at the low, medium and high effort levels — at xhigh or max it returns a 400 error, so to run at those levels you have to switch to adaptive thinking.
What error does turning off thinking return?
The official migration docs give the error verbatim: "thinking.type.disabled" is not supported for this model. Use "thinking.type.between_tools" for the lowest thinking setting, or "thinking.type.adaptive" and "output_config.effort" to control thinking behavior. In short, for the lowest thinking setting use between_tools, and to control thinking behavior use adaptive plus effort — stop sending disabled.
Can I call it on QCode right now?
Yes. claude-sonnet-5-5 has been available on QCode since 2026-09-29, at Sonnet 5's list price. Your existing key still switches between claude-sonnet-5 and claude-opus-5-5 ($4 / $20) by changing the model field only. For the current list and prices, go by the live models page.
Sources
Specs and change list: the Claude Sonnet 5.5 overview page and the model table in Anthropic's official docs (crawled 2026-09-29, covering the release date, model ID, context and maximum output, default effort, per-platform IDs and the five breaking changes). Pricing: the official pricing page, crawled the same day — the per-row unit prices for Sonnet 5.5, Sonnet 5 and Opus 5.5 on input, output and the two cache columns, the Batch rates, the cache-multiplier footnote and the footnote cancelling the Sonnet 5 increase all come from this table. Positioning and self-reported figures: the official launch post claude-sonnet-5-5 (the speed and cost claims, the Terminal-Bench 4.0 score from Anthropic's own testing, Haiku 5.5 in the coming weeks). The error text and between_tools' effort limits: the official migration guide. The default-Sonnet change: the Claude Code changelog 2.1.284.
The newest same-price tier, ready today
Call claude-sonnet-5, claude-sonnet-5-5 (available on QCode since 2026-09-29) and claude-opus-5-5 from one endpoint, billed per token, ready the moment you sign up.
Related reading
Claude Sonnet 5 complete guide
The same-priced previous generation: specs, price list and routing advice.
Claude Sonnet 5 pricing and cost per token
Per-unit pricing, the cancelled 2026-09-01 increase and how caching is billed.
Claude Opus 5.5 complete guide
The tier the vendor reserves for complex work: $4 / $20, cache reads $0.20.
The figures and quotes on this page were checked on 2026-09-29 against Anthropic's official docs and price list; upstream changes may happen without notice. All speed, cost and score numbers are the vendor's own claims or self-testing, not a third-party audit, and are not a promise about your specific workload. Model availability is whatever the on-site models page and your own testing show.