Where it stands
Anthropic has announced Claude Sonnet 5.5, saying it generates output more than 30% faster than Sonnet 5 and can cost up to 30% less per task at unchanged token prices. Its benchmark gains are Anthropic's own reported results, not independent measurements. The model is available through the Claude Platform, Claude products, and Amazon Web Services, Google Cloud and Microsoft Azure. Earlier leak reports matched the model name and listed prices, but the context-window figures they cited do not appear in the announcement.
Anthropic launches Claude Sonnet 5.5 with faster output and lower reported task costs
Anthropic has introduced Claude Sonnet 5.5 as a faster, more efficient successor to Sonnet 5. In a post on X, @claudeai says the model generates output more than 30% faster and can cost up to 30% less per task, even though its listed token prices are unchanged. Anthropic positions it between routine, well-scoped work and the more demanding open-ended tasks intended for Claude Opus 5.5.
The reported improvements cover agentic coding—where a model uses tools and takes multiple steps to complete a task—as well as knowledge work, computer use, visual understanding, and document creation. Anthropic's announcement refers to external testers, but the benchmark, speed, cost-per-task, and tester comparisons below remain results reported by Anthropic rather than independent measurements.
What Sonnet 5.5 changes from Sonnet 5
Anthropic describes Sonnet 5.5 as a complement to Opus 5.5 rather than a universal replacement for it. Sonnet 5.5 is designed for well-scoped everyday tasks, fixing bugs, fast iteration, and producing polished documents, slides, and spreadsheets. Opus 5.5 remains stronger in Anthropic’s testing and that of external testers for complex, open-ended work that requires sustained judgment.
The model’s clearest reported change is efficiency. Anthropic says Sonnet 5.5 typically uses fewer tokens to complete the same work as Sonnet 5. Since token usage affects API costs and can also affect response time, that efficiency is separate from the models’ identical list prices. The company also says Sonnet 5.5 batches tool calls more often in coding tasks, which can reduce the number of steps needed.
Anthropic’s headline Terminal-Bench 4.0 result illustrates the size of the reported coding improvement: Sonnet 5.5 scored 70.6%, compared with 10.3% for Sonnet 5. Terminal-Bench measures complex, multi-step professional tasks completed through a command-line interface. Anthropic reports that Sonnet 5.5’s score was also above the 66.4% result shown for Opus 5.5, although the Opus result used Xhigh effort, its highest reported setting.
Image credit: @claudeai on X
That result should not be read as a general ranking across every task. Anthropic’s announcement says benchmark scores measure only one facet of capability. Its broader table reports Sonnet 5.5 ahead of Sonnet 5 on CursorBench 4.0, GDPval-AA, AA-Briefcase, Humanity’s Last Exam with tools, OSWorld, and Chartography. On several of those evaluations, Opus 5.5 still scores higher.
The benchmark footnotes also matter. Artificial Analysis ran GDPval-AA and AA-Briefcase on a pre-release Sonnet 5.5 deployment that had a structured-output bug. Anthropic says the bug could have degraded responses and has since been fixed, but it does not provide independent confirmation of how much the scores changed. The GPT-6 Sol comparisons also carry version and availability caveats in Anthropic’s table.
Coding and knowledge-work performance
Coding is the area where Anthropic reports the most dramatic difference from Sonnet 5. On FrontierCode 1.1, Sonnet 5.5 scored 46.2% at Max effort and 52.1% at Xhigh effort, compared with 42.4% for Sonnet 5. On CursorBench 4.0, which uses tasks from real Cursor coding sessions, Sonnet 5.5 reached 55.5%, compared with 34.1% for Sonnet 5 and 57.8% for Opus 5.5.
Image credit: @claudeai on X
Those figures also show why the effort setting matters. Sonnet 5.5’s FrontierCode score was lower at Max than at Xhigh. Anthropic attributes the result partly to more frequent use of a code-review skill that split work among subagents; in two examined cases, this led to a timeout or to extra edits beyond the task’s scope. FrontierCode penalizes out-of-scope changes even when they are otherwise useful.
Image credit: @claudeai on X
Anthropic reports similar gains in knowledge work. On GDPval-AA v2.1, which evaluates real-world tasks across 44 occupations and nine industries, Sonnet 5.5 scored 1844 versus 1449 for Sonnet 5 and 1846 for Opus 5.5. On AA-Briefcase v1.1, Sonnet 5.5 scored 1811, compared with 1359 for Sonnet 5 and 1822 for Opus 5.5.
The company also highlights improvements that are harder to reduce to a single score. It says early testers found Sonnet 5.5 more natural for collaboration, better at understanding codebases quickly, and capable of adding polish to interfaces and slide decks. One Anthropic internal test involved creating a 10-slide operating review from earnings materials, call transcripts, and a slide template; two experts judged the first draft ready to send. That is an Anthropic-reported internal test, not independent evidence of typical output quality.
Effort settings change the cost-and-capability trade-off
Effort settings control how long the model reasons and checks its work. Lower settings generally produce faster responses with fewer tokens, while higher settings give the model more time to work through a task. Anthropic says Claude Code and its apps use Medium effort by default, while the Claude Platform defaults to High.
This means the same model can have different cost, speed, and benchmark results depending on how it is configured. Anthropic says Sonnet 5.5 at Low or Medium effort beats Sonnet 5’s best score on several evaluations for about one-tenth of the cost per task. The exact savings vary by benchmark and workload, so that statement should not be treated as a universal per-request price.
Image credit: @claudeai on X
The practical choice is therefore not simply Sonnet 5.5 versus Sonnet 5. Developers need to decide how much effort a task warrants. Low or Medium may suit routine bug fixes, bounded transformations, and quick drafting. Higher settings may be more appropriate when the model must inspect a larger codebase, use tools over many steps, or check a complicated answer. Anthropic’s results suggest that Sonnet 5.5 can approach Opus 5.5 on some tasks at higher settings, but the company still describes Opus as the stronger option for sustained, open-ended judgment.
Image credit: @claudeai on X
Pricing, speed, and availability
Sonnet 5.5 keeps Sonnet 5’s listed token prices: $2 per million input tokens, $10 per million output tokens, and $0.20 per million tokens for cache reads. Anthropic lists cache writes at $2.50 per million tokens for Sonnet 5.5 and $5 for Opus 5.5. Sonnet 5.5’s lower reported cost per task comes from using fewer tokens and taking fewer steps, not from a lower input or output rate.
Anthropic says Sonnet 5.5 generates output more than 30% faster than Sonnet 5, making it the fastest Sonnet model in the company’s comparison. The announcement does not provide a universal latency figure, so the actual difference will depend on the task, effort setting, tool calls, and platform.
The model is available through the Claude Platform, Claude products, Amazon Web Services, Google Cloud, and Microsoft Azure, according to Anthropic. The announcement does not specify regional availability, quotas, plan restrictions, or the exact rollout conditions for each third-party platform.
For developers migrating from a setup that used Sonnet with thinking disabled, Anthropic says Sonnet 5.5 requires the new between_tools setting. That setting keeps up-front thinking disabled, and Anthropic directs users to its migration guide for the details. The announcement does not provide a complete compatibility matrix or migration procedure.
Safety changes and their limits
Anthropic says Sonnet 5.5 matches or improves on Sonnet 5 across most measures in its automated behavioral audit. The company also says the model has cybersecurity capabilities comparable to Opus 5.5, so it is the first Sonnet model to launch with cyber safeguards and fallbacks like those used for Anthropic’s most capable models.
Anthropic describes those cyber safeguards as targeting a narrow set of higher-risk requests. Routine software development, including finding and fixing ordinary bugs, is intended to remain available. Higher-risk cybersecurity tasks may fall back to Sonnet 5, according to the announcement.
The model uses the same biology safeguards as Sonnet 5. Anthropic says most research, education, and clinical work is unaffected, although some microbiology and virology requests may be flagged incorrectly. Its separate Life Sciences Verification Program has its own eligibility, monitoring, retention, and access rules; it should not be treated as a standard Sonnet 5.5 product feature or as evidence that all biology-related requests are unrestricted.
Anthropic also says that no set of evaluations reliably catches every failure, so its reported alignment results are not a guarantee of behavior in every deployment or use case.
Who should consider Sonnet 5.5?
Sonnet 5.5 looks most relevant for teams that need faster iteration on bounded coding and knowledge-work tasks, especially when token usage and response speed matter. It may be a practical upgrade for Sonnet 5 users whose workloads involve bug fixing, codebase understanding, document generation, slide creation, spreadsheet work, or repeated tool-assisted tasks.
The choice is less obvious for highly open-ended work. Anthropic’s own announcement says Opus 5.5 remains clearly stronger for complex tasks requiring sustained judgment. Developers should also test their own prompts, tools, effort settings, output checks, and safety workflows before switching production traffic. The reported benchmark and cost-per-task results are useful signals, but they do not establish that Sonnet 5.5 will be better or cheaper for every application.
For many teams, the most meaningful change may be the combination of unchanged token pricing, lower reported token use, and faster output. Whether that makes Sonnet 5.5 the better choice depends on the task’s complexity, the acceptable error rate, and how much additional reasoning the application needs.
Read Anthropic’s announcement and benchmark notes.
Sources
A Claude Sonnet 5.5 identifier turns up in Claude Code 2.1.284
In a post on X, @lyraxana reports that the model identifier claude-sonnet-5-5 appears in a recent Claude Code update. The attached screenshot identifies the update as Claude Code 2.1.284, replacing 2.1.283, and shows the npm tag next.
That is a signal about what appeared in the update, but it does not by itself confirm that Anthropic has publicly launched Claude Sonnet 5.5 or made it available to users.
What the post reports about Claude Sonnet 5.5
The post says that claude-sonnet-5-5 shows up in the latest Claude Code update. The identifier supports a narrow conclusion: that name was reported as present alongside the update. It does not establish whether the model is released, available as a preview, or being referenced for another form of integration.
What the attached update details show
The attached update notice lists the following version information:
New version:
2.1.284Previous version:
2.1.283npm tag:
next
Image credit: @lyraxana on X
In npm, next is commonly used to identify a prerelease or alternative distribution line rather than the default release line. In this case, however, the screenshot does not establish which users can access that line or what package contents point to claude-sonnet-5-5.
What the evidence does—and does not—confirm
The evidence supports reporting that a model identifier appeared alongside a Claude Code update moving from version 2.1.283 to 2.1.284. It does not confirm:
that Claude Sonnet 5.5 has officially launched;
that the model is generally available or accessible through Claude Code;
how users could access it, or whether access is limited by region or account;
its pricing, capabilities, benchmarks, or context limits; or
whether it replaces another Claude model.
For now, Claude Sonnet 5.5 is best described as a reported model identifier associated with the Claude Code 2.1.284 update, rather than a confirmed public model release.
Sources
Droid registry lists a Sonnet 5.5 entry with an 872,000-token context window
A Droid registry entry labelled “Sonnet 5.5” reportedly lists an 872,000-token context window, a 128,000-token maximum output and five reasoning settings. In a post on X, @LuminaBench shared the entry and warned readers not to interpret its credits as official pricing.
The report comes from Droid’s code rather than an Anthropic announcement or product documentation. The registry entry therefore shows how Droid has represented a model with that name, but does not confirm that Anthropic has officially announced Claude Sonnet 5.5 or that the listed values are final public specifications.
What the Droid registry reportedly lists
A context window is the amount of tokenized input and surrounding information a model can process in a request. The reported entry lists a context window of 872,000 tokens and a maxTokens value of 128000, which appears to represent a maximum output of 128,000 tokens. These are reported registry values, not confirmed Anthropic specifications.
The screenshot also shows the internal model identifier claude-sonnet-5-5 and the display name “Sonnet 5.5.” Other fields include the anthropic-messages wire format and a claude_sonnet_5_5 feature flag. These are implementation details in Droid’s registry, indicating how the application has represented the entry rather than how Anthropic has publicly documented it.
Image credit: @LuminaBench on X
Reported reasoning options and thinking style
The entry lists five reasoning efforts: low, medium, high, xhigh and max. It shows high as the default reasoning effort. The fields appear to give Droid several reasoning settings to select from, but the entry does not explain how each level affects latency, token use, answer quality or cost.
The registry also labels the thinking style as adaptive-summarized. That may describe how Droid expects the model’s reasoning process to be handled, but the entry does not define the implementation or establish that it is a user-visible Anthropic feature.
Which API providers are listed?
The reported apiProviders field names four provider labels:
Anthropic
Vertex Anthropic
Bedrock Anthropic
Azure Anthropic
The labels indicate that the registry includes a direct Anthropic route and hosted-provider variants. They do not establish that Claude Sonnet 5.5 is currently accessible through each provider, that all four routes support the same context or reasoning settings, or that customers can use the model through them.
The credits are not confirmed model pricing
The screenshot shows credits values of 0.8 for input and 5 for output. The post cautions readers not to read those values as pricing and suggests they are credits used by Droid. They should not be treated as official Anthropic rates.
No conversion to dollars, provider billing schedule or public Claude pricing can be established from the registry fields. Readers should not use the displayed credits to estimate the model’s eventual API cost.
What remains unresolved
The registry entry is an early indication of how Droid has configured a model labelled “Sonnet 5.5,” not confirmation of an official Anthropic product release. The report does not establish:
whether Anthropic has officially announced Claude Sonnet 5.5;
when the model might launch or become available;
whether the listed context and output limits are final;
whether the provider labels represent working customer access;
whether the registry values correspond to production behavior; or
whether the model improves on an earlier Claude version.
The reported specifications are therefore best treated as registry data to watch rather than confirmed product documentation. An Anthropic announcement or primary documentation would be needed to establish the model’s official name, capabilities, availability and pricing.
Sources
Sonnet 5.5 reportedly enters grey testing in Claude Code
In a post on X, @chetaslua says Claude Sonnet 5.5 is being grey tested in Claude Code. The post describes the model as fast and efficient and lists prices for input, output and cache reads, but it does not establish an official Anthropic release or general availability.
Image credit: @chetaslua on X
What the post reports about Claude Sonnet 5.5
The post says Sonnet 5.5 is currently being tested in Claude Code. It describes the model as “insanely fast” and efficient, and says it has the “human touch” associated with Sonnet 4. These are the poster’s impressions, not measured results: no benchmark, workload, test conditions or comparison data is provided.
The post also says a comparison with “sol 6” is coming. That comparison is not included, so there are no reported results or test details to assess how Sonnet 5.5 performs against another model.
Reported pricing
The post lists these figures:
Input: $2
Output: $10
Cache reads: $0.20/M
The post does not specify the billing units for the input and output prices. It writes the cache-read figure as “$0.20/M” without defining what “M” represents. Those omissions make the figures difficult to compare with other model prices.
What remains unconfirmed
Nothing in the post establishes that Anthropic has officially announced Claude Sonnet 5.5 or that the model is generally available. The report also does not explain how broad the Claude Code testing is, whether access is limited to selected users, or how someone would obtain access beyond the post’s instruction to use Claude Code.
For now, the report is best understood as an early account of possible Claude Sonnet 5.5 testing, rather than a confirmed release or pricing announcement.
Sources
A post says Sonnet 5.5 could launch soon, with a possible Tuesday window
A post on X says an unreleased model called Sonnet 5.5 has been undergoing stealth testing and could launch soon. The post is not an Anthropic announcement, however, and it provides no confirmed release date or verifiable evidence that the model outperforms Sonnet 5.
In a post on X, @notjazii says the model has been in testing for the last few days and is “looking way better than sonnet 5.” The post suggests Anthropic could release it on the day of the post or around the following Tuesday, but it does not identify the testers or provide a confirmed schedule.
What the Sonnet 5.5 report says
The report describes Sonnet 5.5 as an upcoming model and says early testing has produced better outputs than Sonnet 5. It does not explain what tasks were tested, which prompts were used, who performed the evaluation, or how the results were compared.
It does not establish that Sonnet 5.5 is an officially announced product, that the reported testing occurred under controlled conditions, or that the model consistently outperforms Sonnet 5.
What the reported release window means
The post gives two possibilities: an immediate release or a launch around the following Tuesday. Neither is an official release date.
Readers looking for a “Claude Sonnet 5.5 release date” should therefore treat the suggested window as speculation rather than a schedule. The post does not provide a launch time, access details, pricing, supported products, or information about whether the model would be available through Claude, an API, or another channel.
Why the image is not benchmark evidence
The post points to “these outputs” as evidence that the upgrade is already obvious. But the attached image is a collage of game-controller images labeled “Sonnet 5 xHIGH,” “Sonnet 5.5 xHIGH,” and “GPT 6 SOL xHIGH.” It does not show documented model responses, prompts, scores, or a testing setup.
Because the image does not identify model-generated outputs or explain how the comparisons were produced, it cannot verify the reported improvement. The labels also do not establish that any of the named models were tested or that the image represents an official comparison.
Image credit: @notjazii on X
A meaningful comparison would need at least the prompts, the corresponding outputs, the evaluation criteria, and enough context to reproduce or assess the test. None of that information is included in the post.
What remains unconfirmed
The report does not establish:
Whether Anthropic is developing or testing a model called Sonnet 5.5
Whether the reported testing took place
What improvements, if any, the model has over Sonnet 5
When the model might launch
Which products or users would receive access
Its technical specifications, pricing, or benchmark results
Until Anthropic provides an announcement or other verifiable documentation, the report supports interest in a possible Sonnet 5.5 release—not a confirmed launch date or a demonstrated upgrade.
Sources
Claude Sonnet 5.5 stealth testing reported with 24-hour partner access
A pair of posts on X from @lyraxana reports that Anthropic is stealth testing a model called Claude Sonnet 5.5, with the identifier claude-sonnet-5-5. A follow-up post adds reported details about limited partner access, model settings, tool use and pricing. Neither post independently confirms an Anthropic announcement, public release or the authenticity of those specifications.
What the two posts report
The original post says Anthropic is currently “stealth testing” Claude Sonnet 5.5 and gives the identifier claude-sonnet-5-5. It directs readers to the comments for more information.
In the follow-up, @lyraxana says that partners received access for only 24 hours. The report does not identify those partners or explain what the access involved, so it does not establish broad availability or a public test.
Reported model settings and limits
The follow-up attributes several technical details to the reported model:
A 1M context window
A 128K maximum output
Adaptive thinking enabled by default
The ability to disable thinking only for low, medium or high settings, but not for xhigh or max
These are details reported by @lyraxana, not specifications confirmed by Anthropic or independently tested in the supplied evidence. The posts also do not explain how the reported thinking modes work in practice.
Reported tool-use change and pricing
The follow-up says that forced tool use is retired. It does not define the change or explain which products, APIs or tools it would affect.
It also lists the following pricing:
Input: $2
Output: $10
Cache reads: $0.20/M
The post does not specify the billing unit for the first two figures or define the notation for cache reads. The figures should therefore be reproduced as reported pricing, not presented as confirmed or final Anthropic pricing.
What “stealth testing” means in this report
“Stealth testing” is the wording @lyraxana uses to describe the reported activity. It may suggest testing that is not being broadly announced or made publicly accessible, but the posts do not explain what the testing involves.
The reported 24-hour partner access could describe a limited evaluation arrangement, but the report does not identify the participants, show how access was provided or establish whether the arrangement is still active. It also does not show that Claude Sonnet 5.5 is ready for release or that the public can access it.
What the report still does not establish
The two posts do not provide independent evidence of:
An Anthropic announcement or official position
A public release, API listing or general user access
Final model specifications or pricing
Claude Sonnet 5.5’s capabilities or intended improvements
Benchmark results or independent testing
The scope and outcome of the reported testing
A release date or announcement schedule
A model name, identifier, reported partner access arrangement or listed price does not by itself confirm a completed product launch. The technical details and pricing could be incomplete, provisional, misunderstood or unauthenticated; the supplied evidence does not resolve those possibilities.
How to describe the report accurately
The supplied evidence supports describing this as an unverified report from @lyraxana that Anthropic is testing a model named Claude Sonnet 5.5. The added details remain statements from the post rather than independently confirmed product information.
For now, claude-sonnet-5-5 should be treated as a reported identifier rather than confirmation of a released Anthropic model. An Anthropic announcement, official documentation, an API listing, a model card or reliable independent test results would provide stronger evidence about the model’s status, capabilities, specifications and pricing.
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