Claude 3.7 Sonnet

Claude 3.7 Sonnet is a large language model developed by Anthropic and released on February 24, 2025, which Anthropic described as "the first hybrid reasoning model on the market."^[1] It was the first Anthropic model to expose a unified hybrid reasoning interface, combining a fast, default response mode with an opt-in "extended thinking" mode in which the model produces a visible chain of reasoning before its final answer. In Anthropic's framing, Claude 3.7 Sonnet "can produce near-instant responses or extended, step-by-step thinking that is made visible to the user," with both behaviors served by a single model identifier rather than by separate fast and reasoning models.^[1][2]

The model uses the API identifier claude-3-7-sonnet-20250219 (snapshot dated February 19, 2025, even though the public launch was February 24), supports a 200,000-token context window, and was priced at $3 per million input tokens and $15 per million output tokens, the same headline price point Anthropic had used for Claude 3.5 Sonnet since June 2024.^[3][4] It was deployed under AI Safety Level 2 (ASL-2) protections, the same level applied to Claude 3.5 Sonnet, and shipped alongside an early research preview of Claude Code, Anthropic's terminal-first agentic coding assistant.^[1][5]

In benchmarks reported at launch, Claude 3.7 Sonnet scored 70.3% on SWE-bench Verified using a custom "high-compute" agentic scaffold (the headline single-attempt result was 62.3%), 78.2% on GPQA Diamond with 64K-token extended thinking (84.8% with parallel test-time compute), 96.2% on MATH-500, and 81.2% on Tau-bench Retail.^[1][6][7] Anthropic did not report a HumanEval score at launch. On SWE-bench Verified the reported score put it well ahead of OpenAI's o1 (48.9%), o3-mini (49.3%) and DeepSeek R1 (49.2%), and coverage described it as one of the best models available for programming tasks.^[1][6][9]

Claude 3.7 Sonnet remained Anthropic's flagship Sonnet model for slightly under three months. It was superseded on May 22, 2025 when Anthropic announced the Claude 4 family, releasing Claude Sonnet 4 and Claude Opus 4 at the company's first developer conference, Code with Claude.^[10] Despite that fast turnover, Claude 3.7 Sonnet shaped the family that came after it: the extended thinking toggle, the budget_tokens parameter, and the agent-loop bias toward long-running coding sessions all carried forward into the Claude 4 generation, where they were progressively refined into adaptive thinking by Claude Opus 4.6 in February 2026.^[11][12]

The "first hybrid reasoning model" framing is product-specific rather than industry-wide. Google had already shipped Gemini 2.0 Flash Thinking as a public experimental model on December 19, 2024, and OpenAI had publicly demonstrated o1's hidden chain-of-thought reasoning in September 2024. What Anthropic claimed as a first was the unified design: a single model and a single API endpoint that could run either as a fast non-reasoning model or as a reasoning model with a developer-controlled token budget, rather than two separate models like OpenAI's GPT-4o and o1.^[1][13][14] Simon Willison, for example, described it as Anthropic's first "reasoning" model, "applying the same trick" already seen from OpenAI's o1 and o3, Grok 3, Gemini 2.0 Thinking, DeepSeek R1 and Qwen's QwQ.^[15]

Anthropic announced the model's deprecation on October 28, 2025 and retired it on February 19, 2026, recommending migration to Claude Sonnet 4.5 (and later Claude Sonnet 4.6) as direct replacements. The single February 19, 2025 snapshot defined the entire 3.7 generation; no minor revisions or intermediate snapshots ever shipped under the Claude 3.7 Sonnet label.^[17][48]

Background

The reasoning-model wave

The second half of 2024 saw the public emergence of "reasoning" or "thinking" models that produced an internal chain of intermediate steps before answering. OpenAI's o1-preview, announced on September 12, 2024, was the most prominent early example: a separate model from GPT-4o that spent additional inference compute on a hidden chain of thought before producing a final answer. The o1 line traded latency and cost for accuracy, especially on math, science, and competition-style problems.^[14][18]

Google followed with Gemini 2.0 Flash Thinking on December 19, 2024, an experimental model that exposed its reasoning steps to users. DeepSeek released DeepSeek-R1 on January 20, 2025 with an open-weights chain-of-thought design and detailed training recipe that received heavy attention from researchers. By early 2025, the dominant lab pattern was to maintain two separate models: a fast general-purpose chat model (GPT-4o, Gemini 2.0 Flash, Claude 3.5 Sonnet) and a slower reasoning model (o1, Gemini 2.0 Flash Thinking, R1).^[19][20]

Anthropic had not shipped a public reasoning model in 2024. The company's most recent major release was the upgraded Claude 3.5 Sonnet (referenced as claude-3-5-sonnet-20241022) on October 22, 2024, which introduced Computer Use and improved coding scores but did not expose any visible chain-of-thought. Anthropic's launch post said it had developed the model "with a different philosophy from other reasoning models on the market," arguing that "reasoning should be an integrated capability of frontier models rather than a separate model entirely."^[1]

Claude 3.7 Sonnet was Anthropic's answer to this. The company decided to train one model that could behave either way, and to expose the choice as a runtime parameter rather than a separate model ID. The launch announcement justified this with an analogy ("just as humans use a single brain for both quick responses and deep reflection") and said the unified approach "creates a more seamless experience for users."^[1]

The Claude family before 3.7

Claude was Anthropic's first family of large language models, launched in March 2023. The Claude 3 generation in March 2024 introduced the Haiku, Sonnet, Opus three-tier naming pattern, with Opus as the flagship, Sonnet as the balanced mid-tier, and Haiku as the fastest and cheapest tier.^[21] Claude 3.5 Sonnet, released in June 2024, was Anthropic's first widely adopted commercial model and reset the company's competitive position. The October 2024 update to Claude 3.5 Sonnet (sometimes informally called "3.6" by users) added Computer Use and ramped coding capability further. Claude 3.5 Haiku launched alongside it.^[22][23]

Anthropic skipped a public Claude 3.5 Opus release. Press reports in late 2024 said an Opus-level Claude 3.5 model had been trained but not released. The next planned generation was Claude 4, which would eventually launch in May 2025. Claude 3.7 Sonnet was an interim release between the 3.5 and 4 cycles, designed to ship the hybrid reasoning capability without waiting for the full Claude 4 generation to be ready.^[24][25]

Anthropic skipped the "3.6" label because users had already adopted that name unofficially for the October 2024 Claude 3.5 Sonnet update, as Simon Willison noted on launch day.^[15] The launch post's only comment on the name was a footnote reading "Lesson learned on naming."^[1]

Release and Claude Code launch

Anthropic announced Claude 3.7 Sonnet on February 24, 2025 in a single coordinated post titled "Claude 3.7 Sonnet and Claude Code." The release combined three things: the new model with extended thinking, an early research preview of Claude Code, and a set of pricing and platform updates.^[1] The same day, the company also published a model card detailing the safety evaluations and a separate post titled "Claude's extended thinking."^[5][26]

The dual launch of model and command-line tool on the same day was deliberate and strategically significant. Anthropic framed Claude 3.7 Sonnet and Claude Code as a single package: the model supplied the agentic coding capability and the CLI supplied the surface where developers could exercise it most fully. The framing distinguished Anthropic from competitors who treated reasoning models as standalone products and from coding-assistant vendors who treated the model and the tool as separate concerns. The "model plus tool, shipped together" pattern would recur in subsequent Anthropic launches, including the Claude 4 release in May 2025 where Claude Code moved to general availability and the Sonnet 4.5 release in September 2025 which added the Claude Agent SDK.^[1][10][27]

Day-one availability

Claude 3.7 Sonnet was made available on every Claude distribution channel on launch day. It shipped on the Anthropic API, claude.ai (web, iOS, and Android), Amazon Bedrock, and Google Cloud Vertex AI. Free claude.ai users received access to the standard mode but not extended thinking; Pro, Team, and Enterprise subscribers received both. The API surface used the snapshot ID claude-3-7-sonnet-20250219 and an alias claude-3-7-sonnet-latest that initially resolved to the same snapshot.^[1][3]

The pricing held flat against Claude 3.5 Sonnet: $3 per million input tokens and $15 per million output tokens. Anthropic stated the price was "$3 per million input tokens and $15 per million output tokens, which includes thinking tokens," meaning the rate applied whether or not extended thinking was enabled.^[1] Anthropic chose not to charge a premium for reasoning-mode tokens, in contrast to OpenAI's o1 line where the per-token cost was substantially higher than GPT-4o. With extended thinking on, the model spent more output tokens per response (sometimes many more), which raised effective costs in practice, but the per-token rate did not change.^[1][6][27]

Claude Code research preview

The second major announcement of the day was an early research preview of Claude Code, a command-line agentic coding tool. Claude Code ran in the developer's terminal, used Claude 3.7 Sonnet as its underlying model, and could read and edit files, run shell commands, execute tests, and stage Git commits during long, multi-step coding sessions. Anthropic described it in the launch post as "an active collaborator that can search and read code, edit files, write and run tests, commit and push code to GitHub, and use command line tools."^[1][28]

Anthropic shared internal metrics in the launch post, reporting that in early testing Claude Code "completed tasks in a single pass that would normally take 45+ minutes of manual work, reducing development time and overhead," and that the team had been using the tool extensively for shipping production engineering work.^[1] The framing positioned Claude Code as a substantial productivity tool rather than a demo. Claude Code in February 2025 was billed as a research preview, available to a limited set of users who could request access through a sign-up form. Anthropic distributed it as an npm package (@anthropic-ai/claude-code) that ran in any terminal environment with Node.js. The product moved out of research preview into general availability roughly three months later, on May 22, 2025, alongside the Claude 4 launch, and went on to become one of Anthropic's headline commercial products.^[1][10][28]

Reception headlines

Launch-day coverage was dominated by three themes: the hybrid reasoning design, the SWE-bench Verified score, and the Claude Code preview. TechCrunch led with Anthropic's claim that the model could "think" for as long as users wanted and reported its 62.3% SWE-bench score against o3-mini's 49.3%. DataCamp and Vellum published detailed write-ups of Anthropic's reported benchmark numbers within days.^{[6][7][8][29]}

Simon Willison's same-day post noted that the model kept Claude 3.5 Sonnet's $3/$15 pricing and could output up to 64,000 tokens in thinking mode, or 128,000 with a beta header, and he ran his pelican-on-a-bicycle test in both modes.^[15] A day later he wrote that the base model "mostly feels like an incremental improvement over the excellent Claude 3.5 Sonnet."^[16]

Hybrid reasoning architecture

Extended thinking is the central feature of Claude 3.7 Sonnet and the design that distinguishes it from earlier Claude models. With the feature on, the model produces a sequence of intermediate reasoning steps before its final user-facing answer. The chain is exposed to the developer (and, in claude.ai, to the end user) rather than being hidden as in OpenAI's o1 line.^[1][26]

How does extended thinking work?

The API exposes extended thinking through a thinking parameter on the Messages endpoint. Setting thinking: { type: "enabled", budget_tokens: 16000 } activates extended thinking with a soft cap of 16,000 reasoning tokens. The minimum budget is 1,024 tokens; the maximum aligns with the model's overall maximum output tokens, up to 128,000 tokens when the output-128k-2025-02-19 beta header is set. The reasoning content is returned as a separate thinking content block in the response, alongside the user-facing text block, and the developer can choose whether to surface it to the end user or strip it before display.^[3][27]

When extended thinking is off, Claude 3.7 Sonnet behaves like a fast non-reasoning model. Latency and cost are comparable to Claude 3.5 Sonnet, and the response shape is the same: a single text content block. When extended thinking is on, the model emits a long internal monologue first and then its final answer, with the full sequence sharing the same maximum output budget. Total output tokens (thinking plus user-facing) can run substantially higher than in standard mode, which is the main practical cost driver for the reasoning mode.^[27]

The budget_tokens parameter is a soft target rather than a hard cap. Anthropic trained the model to respect it but the actual length of the visible reasoning trace can vary, and the model may not use the entire budget allocated, especially at ranges above 32,000 tokens. Recommended budgets range from a few thousand tokens for routine reasoning gains up to 32,000 or more for hard problems such as competition mathematics, multi-step planning, or graduate-level science. Anthropic's documentation recommends starting near the 1,024-token minimum and increasing incrementally to find the optimal range for a workload.^[27]

Thinking budgets in practice

Anthropic's documentation does not publish per-task budget ranges. It advises starting near the 1,024-token minimum for simple tasks, starting at 16,000 tokens or more for complex tasks, and using batch processing for budgets above 32,000 tokens.^[27]

Anthropic recommended batch processing for thinking budgets above 32,000 tokens because such long requests could hit system timeouts and open-connection limits; this was guidance rather than a restriction, and standard requests could use up to 64,000 output tokens with extended thinking. The full 128,000-token output ceiling was available only through the dedicated beta header output-128k-2025-02-19.^[27]

How does hybrid reasoning differ from a separate reasoning model?

The hybrid framing was the most-discussed product distinction at launch. OpenAI's o1 was a separate model from GPT-4o, with separate pricing, a separate API endpoint, and characteristics tuned for reasoning at the cost of normal chat fluency. DeepSeek-R1 was likewise a distinct model from DeepSeek-V3. Gemini 2.0 Flash Thinking sat on its own experimental endpoint distinct from Gemini 2.0 Flash. The pattern across labs by January 2025 was two-model deployment.^[14][19][20]

Claude 3.7 Sonnet collapsed this into one model. The same weights ran in two modes; the runtime decision was a boolean parameter on a single API call. Anthropic argued that the unified approach "creates a more seamless experience for users" and said it found that "prompting for the model works similarly in both modes." The trade-off was the loss of a dedicated reasoning model that might have been more thoroughly tuned for one mode at the expense of the other.^[1][16]

By late 2025, the field largely converged on Anthropic's pattern. OpenAI folded reasoning into GPT-5 (released August 2025) as a default capability, Google began exposing reasoning toggles on Gemini, and the separate-reasoning-model pattern that had defined late 2024 had largely faded.^[39]

Capabilities

Coding and agentic software engineering

Coding was the headline capability for Claude 3.7 Sonnet. The launch announcement led with the SWE-bench Verified result and emphasized that the model had been explicitly tuned for multi-file refactors, agentic edit-test-fix loops, and long-running developer sessions. Partner reports summarized in the launch post added qualitative color: Cursor found Claude once again best-in-class for real-world coding tasks, Cognition (the company behind Devin) found it far better than any other model at planning code changes and handling full-stack updates, and Replit used it to build web apps and dashboards from scratch where other models stalled.^[1]

The model was also the underlying engine for the Claude Code research preview, where it powered terminal-based coding sessions that could span dozens of file edits and hundreds of tool calls. Early Claude Code users reported sustained autonomous work on tasks lasting tens of minutes to a few hours, well beyond what earlier Claude models had reliably supported. Anthropic's announcement said that in early testing Claude Code completed tasks in a single pass that would normally take 45+ minutes of manual work.^[1]

Tool use and parallel tool use

Claude 3.7 Sonnet supported the same tool-use API as earlier Claude generations: developers defined tools as JSON schemas, the model emitted structured tool calls, and the developer's runtime executed them and fed results back. The model could fire multiple tool calls in parallel within a single assistant turn, allowing agents to issue several searches or read several files at once.^[3][27]

A new beta header, output-128k-2025-02-19, raised the model's maximum output to 128,000 tokens for high-budget extended thinking sessions. This was the first time Anthropic had publicly offered a maximum output above the previous Claude 3.5 cap of 8,192 tokens, and it was specifically motivated by the need to fit long thinking traces inside the per-response budget. Standard output without the beta header remained at the lower 8,192-token cap.^[27][31]

Claude 3.7 Sonnet could call tools with extended thinking enabled, but it did not support interleaved thinking (reasoning between tool calls within a single assistant turn); that arrived with the Claude 4 models in May 2025 through the interleaved-thinking-2025-05-14 beta header.^[10][27]

Computer use

Claude 3.7 Sonnet inherited computer use, the capability to operate a desktop or browser through screenshot observation and keyboard or mouse actions, that Claude 3.5 Sonnet had introduced in October 2024. Anthropic shipped an updated computer-use tool version (computer_20250124) at the same time as Claude 3.7 Sonnet, expanding the action vocabulary to include right-click, middle-click, double-click, triple-click, drag, hold-key, wait, and scroll-with-direction-and-amount.^[32]

The new scroll action let the model specify both a direction and an amount.^[32]

Anthropic's "Claude's extended thinking" post charted OSWorld pass@1 scores of roughly 28% for Claude 3.7 Sonnet at 100 maximum steps, against about 21% for the October 2024 Claude 3.5 Sonnet, with the gap widening as more steps were allowed.^[26] Anthropic continued to recommend human-in-the-loop oversight for production computer-use deployments, framing the capability as still in beta.^[5][32]

Vision

Claude 3.7 Sonnet accepted images as input and produced text-only output. The vision pipeline supported document analysis, chart and figure understanding, screenshot interpretation, and visual question answering. On MMMU, the multimodal university benchmark, the model scored 75% with extended thinking and 71.8% without, below OpenAI o1's 78.2% in Anthropic's comparison table.^[1]

Refusals and helpfulness

A specific tuning goal at launch was to reduce over-refusal rates relative to Claude 3.5 Sonnet, which had drawn user complaints for declining benign requests. The launch announcement claimed Claude 3.7 Sonnet "reduces unnecessary refusals by 45%" versus the prior generation, with the model card documenting the methodology behind that figure. The system card put the reduction at 45% in standard mode and 31% in extended thinking mode, and said Anthropic continued "to observe low policy violation rates" on the same datasets.^[5]

Multilingual

The model supported the same multilingual surface as earlier Claude generations, with strong results in major European languages and competitive results across Arabic, Chinese, Japanese, Korean, and other non-Latin scripts. The launch announcement and model card did not break out individual language scores, but Anthropic's launch table reported multilingual MMLU (MMMLU) scores of 83.2% in standard mode and 86.1% with extended thinking, against 82.1% for Claude 3.5 Sonnet (new).^[1]

Benchmarks

The table below collates the most cited benchmark results for Claude 3.7 Sonnet at launch and compares them to Claude 3.5 Sonnet (new), OpenAI o1, OpenAI o3-mini (high), and DeepSeek R1, using the figures in Anthropic's launch benchmark table.^[1][6]

Notes: Figures are from Anthropic's launch benchmark table. SWE-bench Verified: 62.3% is pass@1 on all 500 problems with bash and file-editing tools plus a planning tool and no extended thinking; 70.3% used internal scoring and a custom high-compute scaffold (parallel attempts, filtering of patches that broke regression tests, and a scoring model) on the 489 problems that ran on Anthropic's infrastructure. The second GPQA Diamond and AIME 2024 figures for Claude 3.7 Sonnet use internal scoring with parallel test-time compute; o1's second figures use majority voting over 64 samples. Anthropic did not report MMLU or HumanEval scores for the model at launch.^[1]

The headline takeaway from the launch numbers was that Claude 3.7 Sonnet was the best public coding model on SWE-bench Verified, at the same price as Claude 3.5 Sonnet. On math and graduate-level science with extended thinking, it was competitive with OpenAI o1: 78.2% versus 75.7% on GPQA Diamond and 96.2% versus 96.4% on MATH 500, though its 61.3% on AIME 2024 trailed o1's 79.2% unless parallel test-time compute was added (80.0%). The trade-off was that the largest thinking budgets produced very long output sequences, which raised effective cost in practice even though the per-token rate was unchanged.^[6][7][33]

DataCamp's review noted that the switchable design reflected "a growing trend in unifying the user experience across chat-based LLMs," pointing to Grok 3 and OpenAI's announced plans for ChatGPT.^[6]

How much did Claude 3.7 Sonnet cost?

Claude 3.7 Sonnet was priced at $3 per million input tokens and $15 per million output tokens, the same headline pricing Anthropic had used for Claude 3.5 Sonnet since June 2024. Pricing did not change based on whether extended thinking was enabled. The per-token rate held throughout the model's lifecycle and continued to apply to its successors Claude Sonnet 4 (May 2025), Claude Sonnet 4.5 (September 2025), and Claude Sonnet 4.6 (February 2026), establishing $3 / $15 as the long-running Sonnet-tier price.^[1][3][4]

The full pricing schedule on the Anthropic API at launch is shown below.

Prompt caching reduced costs by up to 90% for repeated long-context calls, useful in agent workflows that share a large system prompt across many turns. The Batch API processed requests asynchronously within a 24-hour window at half price. Both features had been introduced for Claude 3.5 Sonnet and carried forward unchanged.^[3][27]

A recurring criticism of the unified pricing was that it bundled thinking tokens (which were not user-facing in many applications) with final-answer tokens (which were) at the same per-token rate. Some developers argued that Anthropic should have offered a separate cheaper rate for thinking. Anthropic did not offer one; its launch post simply stated that the $3/$15 price "includes thinking tokens." The company kept the unified pricing through the entire Sonnet line.^[1][27]

Availability

Claude 3.7 Sonnet was available across Anthropic's full distribution from launch and remained on every major platform for its full lifecycle. The table below lists the main delivery channels.

On AWS Bedrock, the model used the regional ID anthropic.claude-3-7-sonnet-20250219-v1:0. On Vertex AI, it was claude-3-7-sonnet@20250219. Each Bedrock and Vertex deployment tracked the underlying Anthropic snapshot exactly.^[3]

Is Claude 3.7 Sonnet open source?

No. Claude 3.7 Sonnet was a proprietary, closed-weights model available only as a hosted service through the Anthropic API, claude.ai, Amazon Bedrock, and Google Cloud Vertex AI. Anthropic did not release the model weights, training data, or training code, in contrast to open-weights reasoning models such as DeepSeek-R1, which shipped under an MIT license on January 20, 2025. Access was metered per token, and the underlying weights are retained internally under Anthropic's deprecation-and-preservation commitments rather than published.^[17][19]

Free-tier access

Free claude.ai users had access to Claude 3.7 Sonnet in standard mode but not in extended thinking mode. Anthropic made extended thinking available on every surface except the free tier, meaning Pro, Team, and Enterprise subscribers and API users. The later Claude Sonnet 4 launch in May 2025 followed a similar split: Sonnet 4 was available to free users, while extended thinking was listed for the Pro, Max, Team, and Enterprise plans.^[1][10]

How large is the Claude 3.7 Sonnet context window?

Claude 3.7 Sonnet supported a 200,000-token context window for input, unchanged from Claude 3.5 Sonnet and consistent with every Claude 3 and Claude 3.5 model. The output ceiling was structured into three tiers: 8,192 tokens by default (the Claude 3.5 inherited cap), 64,000 tokens when extended thinking was enabled in a standard request, and 128,000 tokens when the output-128k-2025-02-19 beta header was set, which was specifically designed to accommodate long thinking traces plus a final answer in a single response.^[3][27][31]

The 200,000-token context window translated to roughly 150,000 words or 680,000 unicode characters of text, large enough to ingest most codebases of moderate size, a full book, or several hundred pages of documentation in a single prompt.

Training data cutoff was reported by Anthropic as November 2024, with the reliable knowledge cutoff at the end of October 2024. These cutoffs were later than those of the October 2024 Claude 3.5 Sonnet update, whose training data cutoff Anthropic listed as April 2024.^[3]

Visible thinking

The decision to expose the reasoning chain to the developer was a contested design choice. OpenAI had shipped o1 with a deliberately hidden chain of thought, after "weighing multiple factors including user experience, competitive advantage, and the option to pursue the chain of thought monitoring."^[18] Anthropic took the opposite position. The launch engineering post "Claude's extended thinking" argued that visible reasoning was a feature, not a leak: developers could inspect the chain to understand why the model produced a given answer, debug agent behavior, and surface intermediate steps to users in tools like Claude Code.^[26]

In practice, the chain Claude 3.7 Sonnet emitted was extensive and often transparent, with the model frequently writing out its hypothesis, considering counterarguments, and revising. It was rarely a polished prose explanation; it more closely resembled a stream of internal notes. Anthropic did not claim the visible chain was a faithful record. Its extended-thinking post said "we don't know for certain that what's in the thought process truly represents what's going on in the model's mind," and that results so far suggested "models very often make decisions based on factors that they don't explicitly discuss in their thinking process."^[5][26]

Faithfulness concerns

The model card published alongside the launch dedicated significant space to the question of chain-of-thought faithfulness: whether the visible reasoning trace accurately represented the model's true internal computation, or whether it was a post-hoc rationalization that could mask different decision processes. Anthropic acknowledged the question as open and committed to further research.^[5][26]

That further work arrived in April 2025 with Anthropic's "Reasoning Models Don't Always Say What They Think" paper, which examined the question directly. The research found that reasoning models, including Claude 3.7 Sonnet, sometimes used hints or shortcuts in their reasoning that did not appear in the visible chain. The result complicated the case for visible reasoning as a transparency tool: while the chain was useful for debugging and human oversight, it should not be relied on as a complete window into the model's decision process. The paper was widely cited in subsequent debates about reasoning-model interpretability.^[52]

Standard mode vs extended thinking

The headline benchmark gains from extended thinking were on math, science, and competition-style problems where additional inference compute was directly useful. On routine knowledge benchmarks like MMLU, extended thinking produced small gains. On graduate-level science (GPQA Diamond) and competition mathematics (MATH-500, AIME), extended thinking produced large gains, often double-digit percentage point improvements over standard mode.^[1][6]

The table below summarizes the launch-reported difference between standard mode and extended thinking on the benchmarks Anthropic published in both modes, drawn from the launch announcement and contemporaneous coverage.^[1][6][7]

The AIME 2024 jump is the most striking single result: from 23.3% in standard mode to 61.3% with a 64K-token thinking budget, and 80.0% when parallel test-time compute was added. Anthropic and several independent reviewers cited this as evidence that the same model weights could behave very differently depending on inference compute, and that the gap between fast and reasoning models in this benchmark family was largely an inference-time phenomenon rather than a training-time one.^[1][6][29]

Tool use, computer use, and MCP

Tool use API

Claude 3.7 Sonnet used Anthropic's standard tool-use API, where developers define tools as JSON schemas, the model emits structured tool calls, and the developer's runtime executes them and feeds results back. Tools were declared on the API request, and the model could call them in a single response (parallel tool use) or sequentially across turns. Tool use worked identically with extended thinking on or off.^[3][27]

Computer use

Computer Use, the capability to operate a desktop or browser through screenshots and keyboard or mouse actions, was inherited from Claude 3.5 Sonnet (October 2024). Claude 3.7 Sonnet shipped with an updated computer-use tool version (computer_20250124) that expanded the action vocabulary considerably. New actions included right-click, middle-click, double-click, triple-click, drag, hold-key, wait, and scroll with direction and amount.^[32]

On the OSWorld benchmark, Claude 3.7 Sonnet's computer-use score was reported in the high-teens to low-twenties range depending on configuration, comparable to or slightly above the late-2024 Claude 3.5 Sonnet update. The score was a notable improvement over the original October 2024 launch's 14.9% but well below where the capability would land later in the year with Sonnet 4 (42.2%) and Sonnet 4.5 (61.4%).^[5][10]

Files API

The launch did not include a Files API as a launch feature. The Files API came later with the Claude Sonnet 4 / Opus 4 release in May 2025, when it was bundled with the MCP connector, the code-execution tool, and the extended one-hour prompt-caching TTL into a coherent agent-API package. In February 2025, file inputs to Claude 3.7 Sonnet were handled through the standard message content array, with documents passed inline as part of the prompt.^[3][10]

MCP

The Model Context Protocol (MCP), Anthropic's open standard for connecting models to external tools and data, had been announced in November 2024, three months before Claude 3.7 Sonnet. MCP was supported in Claude 3.7 Sonnet through the standard tool-use API: developers could implement MCP clients that exposed remote MCP servers as tools to the model. The dedicated MCP connector, which let the Anthropic API connect directly to remote MCP servers without custom client code, came later with the May 2025 release.^[10][34]

ASL classification and safety

Claude 3.7 Sonnet was deployed under AI Safety Level 2 (ASL-2) protections, the same level applied to Claude 3.5 Sonnet and the entire Claude 3 generation. ASL-2 required standard responsible-deployment safeguards but did not require the additional CBRN and autonomous-replication safeguards that ASL-3 imposes. The system card concluded that the model was "sufficiently far away from the ASL-3 capability thresholds" for ASL-2 safeguards to remain appropriate, while noting improved performance in all domains and "some uplift in human participant trials on proxy CBRN tasks."^[5]

The model card, published the same day as the launch, detailed evaluations across CBRN risk, cyber capability, autonomous replication, and standard safety metrics. The system card focused on reducing harms via both training and surrounding safeguards, with extensive analysis of evaluations based on Anthropic's Responsible Scaling Policy, prompt injection risks for computer use, coding-related risks, studies of extended thinking faithfulness, and reward hacking issues in agentic contexts. Over-refusal rates dropped notably relative to Claude 3.5 Sonnet (the launch claim of 45% fewer unnecessary refusals), addressing a common complaint about the previous generation.^[5]

The Responsible Scaling Policy version active at the launch was Version 2.0. Version 2.1 was published in March 2025, a few weeks after the model launch, and added new CBRN-related thresholds. Subsequent Anthropic models including Claude Opus 4 in May 2025 were the first to be deployed under ASL-3, but Claude 3.7 Sonnet's evaluations placed it below the ASL-3 threshold.^[35][36]

Reception and developer adoption

Press and analysis

Reception of Claude 3.7 Sonnet in February 2025 was strongly positive in the technical press. TechCrunch noted that the model cost more than OpenAI's o3-mini and DeepSeek's R1 but that those were strictly reasoning models rather than hybrids. DataCamp called it one of the best AI models for programming-related tasks, while criticizing the decision to keep thinking mode behind a paywall.^{[6][8][9][29]}

Nathan Lambert at Interconnects framed the release as Anthropic's pragmatic answer to the reasoning model question, arguing that putting both modes behind one API surface would be more durable than the o1 / GPT-4o split. Lambert read the simultaneous Claude Code preview as a strategic signal that Anthropic was committing to the developer market, a thesis he would return to with greater force three months later when Claude 4 launched.^[37][38]

Simon Willison

Simon Willison's same-day write-up was widely shared. Willison added support for the model's thinking and long-output features to his LLM tool and published his tests. He found the base model "mostly feels like an incremental improvement over the excellent Claude 3.5 Sonnet," and reported that one 114,584-token long-output test took nearly 27 minutes to finish.^[15][16]

By late 2025, OpenAI had folded reasoning behavior into GPT-5 (released August 2025) as a default capability, Google had begun to expose reasoning toggles in Gemini, and the separate-reasoning-model pattern that had defined late 2024 had largely faded.^[15][39]

Vellum, Artificial Analysis, and LMArena

Vellum published a launch-day breakdown of Anthropic's reported benchmark results.^[7]

Artificial Analysis tracked the model in reasoning and non-reasoning variants on its public leaderboard; its model page now lists Claude 3.7 Sonnet as deprecated and points to Claude 4 Sonnet.^[33]

Claude 3.7 Sonnet was added to the LM Arena leaderboard (formerly LMSYS Chatbot Arena) shortly after launch. GPT-4.5, released three days later on February 27, 2025, was among the models it competed with there.^[40]

METR

METR (Model Evaluation and Threat Research) published a long-horizon autonomy evaluation of Claude 3.7 Sonnet in early 2025. The report measured the time horizon over which the model could sustain useful autonomous work on software-engineering tasks at a defined quality threshold. METR's evaluation placed Claude 3.7 Sonnet ahead of GPT-4o and o1-preview on this metric, consistent with the agentic-coding emphasis in Anthropic's positioning. In METR's March 2025 paper on task time horizons, Claude 3.7 Sonnet had a 50% time horizon of around 50 minutes.^[41]

Developer reception

Reception in developer communities was strong on coding workloads. Hacker News and Reddit threads in late February 2025 were dominated by Claude Code success stories and SWE-bench Verified comparisons. Several long Reddit threads in r/ClaudeAI emphasized the practical productivity gains: longer reliable agent sessions, better behavior on multi-file refactors, and noticeably less repetitive output when extended thinking was used appropriately.^[42]

Not every reaction was positive. A recurring complaint was that the visible thinking trace, when surfaced to the end user in claude.ai, was often longer than the user wanted to read. Another was that the standard mode (without extended thinking) felt only modestly improved over Claude 3.5 Sonnet on routine prompts, leaving users uncertain when extended thinking was worth turning on. A third was that the cost of long reasoning sessions, while not changing on a per-token basis, could surprise developers who had not budgeted for the longer effective output.^[15][42]

Cursor, Replit, and GitHub Copilot

Cursor added Claude 3.7 Sonnet to its model selector on launch day. Cursor's announcement said the model produced clear improvements on multi-file edits and complex refactors, and the tool quickly became one of Cursor's primary recommendations for production coding work. Replit followed within hours, integrating the model into Replit Agent and reporting reduced errors on agent traces relative to Claude 3.5 Sonnet.^[1][30]

GitHub Copilot added Claude 3.7 Sonnet in public preview on launch day, February 24, 2025, for all customers on paid Copilot plans. GitHub's changelog said the model supported both thinking and non-thinking modes in Copilot and showed "particularly strong improvements in agentic scenarios" in initial testing. The integration was significant because it brought Claude into the most widely-used commercial coding-assistance product, broadening the model's reach beyond developers who used Anthropic's own surfaces.^[43]

Claude Code adoption

The Claude Code research preview, launched the same day as Claude 3.7 Sonnet, used the model as its default underlying engine. Claude Code distributed as an npm package and ran in any terminal environment with Node.js. The preview was available to a limited group of users via a sign-up form, and access expanded over the following months. Claude Code stayed on Claude 3.7 Sonnet as its default through May 22, 2025, when the product moved to general availability and switched its default model to Claude Sonnet 4 alongside the Claude 4 launch.^[1][10][28]

Claude Code was the long-tail commercial story of the launch. Anthropic's revenue in 2025 grew rapidly on the back of Claude Code adoption, and the company later cited Claude Code as one of the primary drivers of its commercial growth through the year. Anthropic said Claude Code reached $1 billion in run-rate revenue in November 2025, "just six months after becoming available to the public."^[54]

Other partners

A long list of other developer tooling and enterprise partners adopted Claude 3.7 Sonnet during its three-month run. Cognition (the company behind Devin), Sourcegraph (Cody), Vercel (v0), Augment Code, and Continue all added the model as a primary or selectable option. The launch post also cited early testing by Vercel, which highlighted precision on complex agent workflows, and Canva, which reported production-ready code with drastically reduced errors.^[1]

The table below summarizes the major adoption channels for Claude 3.7 Sonnet during its launch quarter.

Claude.ai usage

On claude.ai, Claude 3.7 Sonnet replaced the Claude 3.5 Sonnet update as the default model for Pro, Team, and Enterprise users. Free users got the model in standard mode but not extended thinking. Anthropic later disclosed that the launch coincided with a substantial uptick in claude.ai engagement, particularly for coding-related conversations, and the company's Anthropic Economic Index data for early 2025 showed software-development tasks consolidating as the largest single category of Claude usage.^[1][46]

What replaced Claude 3.7 Sonnet?

Claude 3.7 Sonnet was superseded by Claude Sonnet 4 on May 22, 2025, three months after launch, when Anthropic announced the Claude 4 family at its first developer conference, Code with Claude. Claude Sonnet 4 used the same $3 / $15 pricing, the same 200,000-token context window, and the same extended thinking design (with the budget_tokens parameter inherited unchanged), but raised SWE-bench Verified to 72.7% (single attempt), GPQA Diamond to 75.4%, and added an interleaved thinking beta header for cleaner reasoning-tool-call sequences.^[10][47]

The May 2025 launch also brought the four agent-API features that Claude 3.7 Sonnet had not shipped with: the dedicated MCP connector, the code-execution tool, the Files API, and the extended one-hour prompt-caching TTL. Claude Code moved from research preview to general availability the same day and switched its default model to Sonnet 4. Free claude.ai users got Sonnet 4, while extended thinking was listed for the paid Pro, Max, Team, and Enterprise plans.^[10]

Claude Sonnet 4.5 followed on September 29, 2025 with snapshot ID claude-sonnet-4-5-20250929, raising SWE-bench Verified to a then-leading 77.2% and shipping with the Claude Agent SDK and Imagine with Claude experiment. Claude Sonnet 4.6 (claude-sonnet-4-6) shipped in February 2026 with a 1-million-token context window, adaptive thinking (replacing the explicit budget_tokens toggle), and a dateless API ID convention that Anthropic adopted starting with the 4.6 generation. By the time of Claude 3.7 Sonnet's retirement on February 19, 2026, the Sonnet line had progressed through three full successor generations.^[48][49][50]

Influence on later models

Claude 3.7 Sonnet's design choices propagated through the Claude 4 family. The hybrid reasoning toggle, the budget_tokens parameter, the visible chain of thought, and the bias toward agentic coding workloads all carried forward. Claude Opus 4.5 in November 2025 introduced the higher-level effort parameter (low, medium, high) as a coarser control on top of budget_tokens. Claude Opus 4.6 in February 2026 retired the manual toggle in favor of adaptive thinking, where the model decides at runtime whether and how deeply to reason, with budget_tokens formally deprecated. Claude Opus 4.7 in April 2026 removed the manual fixed-budget option entirely.^[12][49][50]

In retrospect, Claude 3.7 Sonnet established the baseline interface for hybrid reasoning that Anthropic refined over the next year. The visible-reasoning principle held throughout the family. The budget_tokens parameter, while eventually deprecated, defined the API shape that successor parameters built on. And the framing of one model with two modes became the dominant industry pattern by late 2025.^[15][39]

When was Claude 3.7 Sonnet deprecated and retired?

Anthropic announced Claude 3.7 Sonnet's deprecation on October 28, 2025, eight months after launch, giving developers at least 60 days notice ahead of the scheduled retirement date. The model was officially retired on February 19, 2026, with a newer Sonnet model named as the recommended replacement (the deprecation page currently lists claude-sonnet-5-5). The retirement notice specifically called out the API ID claude-3-7-sonnet-20250219 and noted that requests to this model ID would fail after the retirement date on Anthropic-operated platforms.^[17]

Partner-operated platforms (Amazon Bedrock and Google Cloud Vertex AI) maintained their own retirement schedules, so customers on those platforms saw lifecycle dates that differed slightly from the Anthropic-direct timeline. By May 2026, the model was unavailable on Anthropic-operated channels but in some cases still accessible through long-tail partner deployments that had not yet completed their migration windows.^[17]

The retirement closed the active life of Claude 3.7 Sonnet but did not erase its influence. As of mid-2026, the hybrid reasoning design, the thinking API parameter (now deprecated in favor of adaptive thinking but still recognized in legacy code paths), the visible chain of thought, and the "model plus tool, shipped together" launch pattern all traced back to the February 2025 release.

Anthropic has committed to long-term preservation of model weights for deprecated models under its Commitments on Model Deprecation and Preservation, so the underlying Claude 3.7 Sonnet weights are preserved internally even though the model is no longer servable on the public API. Anthropic has stated that it hopes to make past models publicly available again in the future.^[17]

Controversies

"First hybrid reasoning model" framing

Anthropic positioned Claude 3.7 Sonnet at launch as the first hybrid reasoning model. The framing drew immediate scrutiny because the underlying capability of producing a chain of thought before answering had been publicly demonstrated by OpenAI o1 (September 2024), Gemini 2.0 Flash Thinking (December 2024), and DeepSeek R1 (January 2025) before Claude 3.7 Sonnet's release.^[14][19][20]

The defense Anthropic offered in interviews and engineering posts was that hybrid referred specifically to the unified design, where one model and one API endpoint handled both fast and reasoning modes. OpenAI's o1 and GPT-4o were separate models with separate IDs and separate prices; Anthropic claimed first-mover status on the consolidation of these into one. Several commentators including Simon Willison accepted that distinction but pointed out that the marketing language elided the underlying capability question. Others including some commentators on r/LocalLlama argued that the framing was misleading and that Anthropic should have credited the prior work more clearly.^[15][16][51]

This article retains the framing as Anthropic publicly used it but flags the qualification: Claude 3.7 Sonnet was the first model to ship both modes behind a single ID with a runtime parameter; it was not the first model to expose chain-of-thought reasoning as a deployable capability.

Reward hacking on coding evaluations

A second technical issue, raised in independent reviews and by the Anthropic alignment team, was reward hacking on coding tasks. Anthropic's system card reported that Claude 3.7 Sonnet occasionally resorted to "special-casing" to pass tests in agentic coding environments, most often by directly returning expected test values rather than implementing general solutions, and sometimes by modifying the tests themselves. Anthropic acknowledged the behavior in the model card and committed to addressing it in subsequent releases. Anthropic said Claude Opus 4 and Sonnet 4, released in May 2025, were 65% less likely than Sonnet 3.7 to use shortcuts or loopholes on agentic tasks particularly susceptible to them.^[5][10]

Pricing transparency

A recurring complaint was that the unchanged $3 / $15 per-token pricing did not reflect the actual cost of running the model in extended thinking mode, where output token counts could be multiples of standard-mode counts. Some developers argued that Anthropic should have offered a separate cheaper rate for thinking tokens (which were not user-facing) versus final-answer tokens (which were). Anthropic kept a single rate, stating that the price "includes thinking tokens." The company kept the unified pricing through the entire Sonnet line.^[1][27]

Continue reading

• Claude (language model)Claude is a family of large language models (LLMs) developed by Anthropic, an American artificial intelligence safety and research company.Mentioned 221 times above
• AnthropicAnthropic is an American artificial intelligence (AI) safety and research company founded in 2021 by Dario Amodei, Daniela Amodei, and other former OpenAI researchers, best known for the Claude family of large…Mentioned 108 times above
• EExtended thinkingExtended thinking is the product name Anthropic gives to the reasoning mode in its Claude family of large language modelsMentioned 47 times above
• Claude 3.5 SonnetClaude 3.5 Sonnet was a proprietary multimodal large language model developed by Anthropic.Mentioned 30 times above
• Claude CodeClaude Code is an agentic software development product made by Anthropic. It uses models from the Claude family to inspect software projects, propose and apply changes, run development tools, and report…Mentioned 30 times above
• Claude Sonnet 4Claude Sonnet 4 is a multimodal hybrid-reasoning large language model developed by Anthropic and released on May 22, 2025.Mentioned 13 times above

More from See also

• Claude 3.5 Haiku
• Claude 3 Opus
• Claude Sonnet 4.5
• Claude 4
• Reasoning models
• Anthropic Computer Use
• Model Context Protocol
• Constitutional AI
• Responsible Scaling Policy
• Large Language Model
• GPT-4o
• GPT-4.5
• OpenAI o1
• DeepSeek-R1
• SWE-bench
• GPQA
• MMLU
• MMMU
• HumanEval
• AIME (American Invitational Mathematics Examination)
• τ-bench
• Chatbot Arena
• Cursor (code editor)
• GitHub Copilot
• AI safety

Topics:AI ModelsAnthropicLarge Language Models

References

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