Claude Opus 4.1

Claude Opus 4.1 is a large language model developed by Anthropic and released on August 5, 2025. It is the first incremental update to the Opus tier of the Claude 4 family, succeeding Claude Opus 4 (May 22, 2025) and preceding Claude Opus 4.5 (November 24, 2025). Anthropic positioned the release as a focused upgrade for agentic tasks, real-world coding, and research-style reasoning, with pricing held flat at $15 per million input tokens and $75 per million output tokens to encourage existing Opus 4 customers to migrate.^[1][2]

The headline benchmark for Opus 4.1 was SWE-bench Verified, where the model advanced Anthropic's state of the art for real-world software engineering from 72.5% (Opus 4) to 74.5%. Smaller but consistent gains showed up across most other reported evaluations, including Terminal-bench, GPQA Diamond, AIME 2025, MMLU (in its multilingual MMMLU variant), and MMMU validation. The one regression Anthropic disclosed was on the airline split of tau-bench, which dropped 3.6 percentage points relative to Opus 4.^[3][4][5]

Anthropic released the model with API identifier claude-opus-4-1-20250805, kept the 200,000 token context window and 32,000 token maximum output of Opus 4, and shipped the model simultaneously to claude.ai paid tiers, Claude Code, the Claude API, Amazon Bedrock, and Google Cloud Vertex AI. The model was deployed under Anthropic's Responsible Scaling Policy at AI Safety Level 3 (ASL-3), the same standard as Opus 4. Anthropic published a short system card addendum rather than a full new system card, on the basis that Opus 4.1's capability gains did not cross the thresholds that would require fresh red-team evaluations.^[1][6][7]

Opus 4.1 served as Anthropic's flagship for roughly 16 weeks before being overtaken by Claude Sonnet 4.5 on agentic coding (September 29, 2025) and then formally superseded at the Opus tier by Claude Opus 4.5 on November 24, 2025. The model carried a tentative retirement date of "not sooner than August 5, 2026," and was relegated to the "Legacy models" section of Anthropic's models documentation by early 2026 as Opus 4.5 became the default Opus offering. As of May 2026, Opus 4.1 was the only base-generation Claude 4 Opus snapshot still in "Active" status on the API, after Anthropic deprecated claude-opus-4-20250514 on April 14, 2026 without folding Opus 4.1 into the same deprecation wave. Anthropic then announced the deprecation of Opus 4.1 on June 5, 2026 and retired it from the Claude API on August 5, 2026, naming claude-opus-4-8 as the recommended replacement.^[8][9][36]

What led to Claude Opus 4.1?

Anthropic announced the Claude 4 family on May 22, 2025 with the simultaneous launch of Claude Opus 4 and Claude Sonnet 4. Opus 4 was Anthropic's first model deployed under the ASL-3 deployment and security standard. It introduced hybrid reasoning, a 200,000 token context window, a 32,000 token maximum output, and a substantially deeper investment in agentic software engineering than any prior Claude model. The Opus 4 launch also marked the general availability of Claude Code, Anthropic's terminal coding agent, after a research preview that began alongside Claude 3.7 Sonnet in February 2025.^[10][11]

By midsummer 2025 the model landscape around Claude 4 had shifted. OpenAI was preparing to launch GPT-5 (which arrived on August 7, 2025, two days after Opus 4.1), and Google's Gemini 2.5 Pro was already on the market with strong reasoning scores. Anthropic was simultaneously feeling competitive pressure from xAI's Grok 4 and from open-weights coding models tuned for SWE-bench. Anthropic's launch customers highlighted multi-file refactoring, precise edits that avoided unnecessary changes, and gains on a junior-developer benchmark. Anthropic chose to ship a focused increment rather than wait for a larger generation step, an approach the company would repeat several times over the next nine months.^[1][2][12]

The Opus tier had also drifted out of step with the rest of the family. By early August 2025, Sonnet 4 was the model most enterprise customers actually used in production, both because of cost and because the gap between Opus 4 and Sonnet 4 was smaller than the gap between equivalent Opus and Sonnet pairings in earlier Claude generations. Anthropic needed Opus 4.1 to widen that gap, especially on the long-horizon coding work where a higher per-token price was still defensible. The customer references in the launch post (GitHub on multi-file refactoring, Rakuten on surgical edits in large codebases, Windsurf on a junior-developer benchmark) all targeted exactly the kind of difficult, long-horizon engineering work that justified the $15/$75 Opus tier rather than dropping down to the cheaper $3/$15 Sonnet tier.^[1][2]

Outside commentators read the version number literally. Simon Willison wrote in his August 5 launch post: "treating this as a .1 version increment looks like it's an accurate depiction of the model's capabilities."^[3]

When was Claude Opus 4.1 released?

Anthropic announced Claude Opus 4.1 in a short blog post on August 5, 2025 titled "Claude Opus 4.1." The release post described the model as "an upgrade to Claude Opus 4 on agentic tasks, real-world coding, and reasoning" and called out three customer-quoted improvements. GitHub said that "Claude Opus 4.1 improves across most capabilities relative to Opus 4, with particularly notable performance gains in multi-file code refactoring." Rakuten Group said the model "excels at pinpointing exact corrections within large codebases without making unnecessary adjustments or introducing bugs." Windsurf said 4.1 "delivers a one standard deviation improvement over Opus 4 on their junior developer benchmark," comparable to the jump from Sonnet 3.7 to Sonnet 4.^[1]

The release went out simultaneously across all Anthropic surface areas: paid claude.ai tiers (Pro, Max, Team, and Enterprise), Claude Code, the Anthropic API, Amazon Bedrock, and Google Cloud Vertex AI. Pricing matched Opus 4 exactly at $15 per million input tokens and $75 per million output tokens, with prompt caching write at $18.75 per million tokens (a 1.25x premium for the standard 5-minute cache) and cache read at $1.50 per million tokens (a 90% discount on cached input). The model used the API identifier claude-opus-4-1-20250805, with the convenience alias claude-opus-4-1 resolving to that snapshot.^[1][2][13]

The Bedrock identifier was anthropic.claude-opus-4-1-20250805-v1:0, available at launch in US West (Oregon), US East (N. Virginia), and US East (Ohio); the Vertex AI identifier was claude-opus-4-1@20250805, available in Anthropic's standard Vertex partner regions. Cross-platform parity was a deliberate Anthropic positioning choice: enterprise customers running through Bedrock or Vertex did not need to wait for a separate availability announcement, and the model behavior was identical regardless of how it was reached.^[2][13]

Anthropic also signaled in the post that further upgrades were imminent, writing that "we plan to release substantially larger improvements to our models in the coming weeks." That promise was kept later in 2025, with Claude Sonnet 4.5 arriving on September 29, Claude Haiku 4.5 on October 15, and Claude Opus 4.5 on November 24. From the announcement of Opus 4.1 to the release of Opus 4.5 was 111 days, longer than any other gap between consecutive Opus releases from Opus 4 through Opus 4.8 (the Opus 4 to Opus 4.1 gap was 75 days, and later gaps were 73, 70 and 42 days).^[14][15][8]

Knowledge cutoff and tokenizer

Anthropic listed Opus 4.1 with a reliable knowledge cutoff of January 2025 and a training data cutoff of March 2025, both unchanged from Opus 4. The reliable cutoff is the date through which Anthropic considers the model's knowledge most extensive and reliable, and the training data cutoff is the broader date range of training data used. Opus 4.1 used the same tokenizer as Opus 4 and the rest of the Claude 4 family; the new tokenizer that defined the Claude Opus 4.7 generation was still more than eight months in the future at launch.^[2][13]

How does Claude Opus 4.1 perform on benchmarks?

Anthropic's announcement of Opus 4.1 included a comparison chart against Opus 4 covering eight benchmarks. SWE-bench Verified and Terminal-bench were reported without extended thinking; tau-bench, GPQA Diamond, MMMLU, MMMU, and AIME 2025 were reported with extended thinking enabled at up to 64,000 reasoning tokens. The full table is reproduced below.^[1][3]

Headline benchmarks vs Opus 4

The largest absolute gain came on Terminal-bench, an evaluation of long-running terminal sessions where the model has to plan, execute, and recover from shell commands. The gain on SWE-bench Verified was smaller in percentage-point terms but more closely watched, because SWE-bench Verified had become the de facto industry yardstick for real-world software engineering. Anthropic did not attribute the SWE-bench gain to any specific change, though Rakuten's comment about avoiding "unnecessary adjustments" pointed in the same direction.^[1]

Anthropic noted in the methodology fine print that the tau-bench scores were "achieved with a prompt addendum to both the Airline and Retail Agent Policy" and that the maximum number of agent steps had been increased from 30 to 100. Anthropic said the higher limit was there "to accommodate the additional steps Claude incurs by utilizing more thinking," and that most trajectories still finished in under 30 steps, with only one going above 50. The scores therefore come from a modified harness and are not directly comparable with tau-bench results run under the original setup.^[1]

The drop on tau-bench Airline was the only regression Anthropic published. The airline split tests sustained negotiation with a multi-step constrained API, and the regression suggested that the post-training mix that improved code refactoring may have shifted policy slightly on certain customer-service style multi-turn dialogues. Anthropic did not provide a detailed explanation, and partner-side reports did not flag the regression as practically significant.^[3]

What specifically improved over Opus 4

Beyond the raw scores, Anthropic and several partners described qualitative behavior changes:

• Multi-file refactoring. GitHub reported that 4.1 was meaningfully better than 4 at editing several related files in one pass without introducing collateral changes elsewhere. This was the single most cited improvement in launch coverage.^[1][16]
• Detail tracking. Anthropic specifically highlighted "in-depth research and data analysis" gains, "especially around detail tracking and agentic search," language that maps to longer-horizon agent traces where the model has to remember intermediate findings.^[1]
• Tool-call discipline. The Terminal-bench gain implies more reliable use of shell tools, recovery from errors, and adherence to plans across extended runs. Cognition and other agent-focused builders reported anecdotal improvements in long traces.^[16][17]
• Surgical edits. Rakuten's quote in the launch post emphasized that 4.1 made fewer "unnecessary adjustments," a recurring complaint about Opus 4 on production codebases.^[1]

The model did not change architecture in any way Anthropic publicly disclosed. The 200,000 token context window, 32,000 token maximum output, hybrid reasoning toggle, vision input, and tool-use schemas were all carried over from Opus 4 unchanged.^[1][2][13]

The improvements concentrated in places that mattered for production engineering work. Multi-file refactoring is the kind of task where the cost of a single mistake propagates: an unwanted change to a shared utility breaks tests in many other files, and the model has to reason about callers as well as callees. Anthropic's launch language suggested that the post-training data and reward modeling for Opus 4.1 specifically targeted this case. The Windsurf comparison to "the jump from Sonnet 3.7 to Sonnet 4" was meaningful precisely because that earlier jump had been one of the more significant within-tier changes in Anthropic's history, and Windsurf's internal evaluations were one of the toughest external coding signals around.^[1][3]

Anthropic also emphasized that Opus 4.1 was not chasing a single number on a single leaderboard. The launch post led with the 74.5% SWE-bench Verified figure but gave equal space to research-and-data-analysis gains and to three customer reports rather than a long list of records. That positioning matched the version label: a 4.1 release that nudged real workflows along rather than redefining the model class.^[1]

Comparison to GPT-5 and to later Opus models

GPT-5 launched on August 7, 2025, two days after Opus 4.1, and on its launch chart OpenAI reported 74.9% on SWE-bench Verified, narrowly above Opus 4.1's 74.5%. Independent comparisons over the following weeks generally placed the two models within noise of each other on coding and within a few percentage points on hard reasoning, with GPT-5 ahead on some math and academic benchmarks and Opus 4.1 ahead on several agentic and tool-use evaluations. The Scale SWE-bench Pro leaderboard, a tighter version of SWE-bench, showed both models near the top with Opus 4.1 at 22.7% on the public split and 17.8% on the private split versus GPT-5 at 23.1% public and 14.9% private, with Scale noting that both models performed more consistently across languages and repositories than lower-ranked models.^[18][19]

The picture changed sharply at the next release tier. The table below puts Opus 4.1 alongside GPT-5 and the next Opus generation.

[a] Opus 4.5 emphasized agentic and SWE-bench evaluations and downplayed older academic benchmarks at launch. Opus 4.7's launch materials similarly led with agentic, vision, and finance evaluations rather than AIME-style math.^[8][37]

The pricing column captures the most dramatic context for Opus 4.1's place in history. At its launch, Opus 4.1 was the most expensive model in Anthropic's lineup; by November, Opus 4.5 was offering substantially better performance at one third of the price, and OpenAI was already pricing GPT-5 an order of magnitude lower than Opus 4.1 on inputs and roughly seven times lower on outputs. The economics of running Opus 4.1 in production thus deteriorated rapidly across its 111 days as the flagship Opus model, and the gap widened further as Opus 4.5 (November 2025), Opus 4.6 (February 2026), and Opus 4.7 (April 2026) each held the $5 / $25 price line while moving SWE-bench Verified from 80.9% to 80.8% to 87.6%. By April 2026 the published Anthropic gap on SWE-bench Verified between Opus 4.1 and the then-current Opus 4.7 was roughly 13 percentage points, at one third of Opus 4.1's per-token price.^{[8][2][18][37][38]}

Independent measurements

Artificial Analysis tracked Opus 4.1 in its non-reasoning category. In a February 2026 snapshot of its model page, the model scored 24 on the site's Intelligence Index, 20th of 58 non-reasoning models, which the site described as "above average in intelligence, but particularly expensive"; its measured output speed of about 38 tokens per second placed it 39th of 58, and the site called it "notably slow." Its $15 input and $75 output list prices ranked 55th and 56th of 58 on cost. An August 2025 snapshot had measured about 23 tokens per second with a time to first token of about 1.6 seconds.^[20][41]

LM Arena added Opus 4.1 to its Text Arena and WebDev Arena leaderboards on August 11, 2025 and to its Search Arena on August 26, 2025. A "Claude Opus 4.1 Thinking" variant was added to the Text and WebDev leaderboards on August 18, 2025.^[21]

TechRepublic's launch coverage focused on practical availability: it reported that GitHub Copilot had added Opus 4.1 for Enterprise and Pro+ subscribers (in Visual Studio Code only in ask mode), with Opus 4 remaining an option for a 15-day transition period, and it quoted The Neuron newsletter's caveat that at $75 per million output tokens Opus 4.1 "costs 5x more than Sonnet 4 (but that's the same as current Opus 4)."^[28]

How much does Claude Opus 4.1 cost?

Pricing for Opus 4.1 matched Opus 4 exactly across every surface, a deliberate signal from Anthropic that customers should treat 4.1 as a drop-in replacement.

Through claude.ai, Opus 4.1 was available to Pro, Max, Team, and Enterprise tier users. It was available through Claude Code from launch and replaced Opus 4 as the default Opus model in Claude Code shortly after release. On the API, the snapshot identifier was claude-opus-4-1-20250805 and the convenience alias was claude-opus-4-1. The model was simultaneously available as anthropic.claude-opus-4-1-20250805-v1:0 on Amazon Bedrock and as claude-opus-4-1@20250805 on Google Cloud Vertex AI.^[2][13]

The 200,000 token context window was unchanged from Opus 4 and remained the Opus-tier context length until Opus 4.6 brought a one million token context window (in beta) to the Opus tier in February 2026. Maximum output tokens were also unchanged at 32,000 (synchronous Messages API). Extended thinking on Opus 4.1 followed the same toggle and budget mechanics as on Opus 4 and Sonnet 4: developers set a budget_tokens value (up to 64,000) and the model spent that budget on a chain-of-thought scratchpad before producing the final answer.^[13][23]

Cost calculation walkthroughs

Production teams running Opus 4.1 quickly learned that prompt caching changed the practical cost equation. A typical Claude Code session sending 50,000 tokens of repository context plus 5,000 tokens of new prompt would cost $0.825 on a cold call ($15 x 0.055M). Once that 50,000 token prefix was in the 5-minute cache, follow-up calls cost roughly $0.075 for the cache read plus $0.075 for the new 5,000-token tail, for a total of $0.15. The cache write itself cost $0.94 (50,000 x $18.75 / 1M), so the breakeven point was a single follow-up call rather than several.^[1][2][13]

For longer-running agent traces, the 1-hour cache option (introduced family-wide in mid-2025) added another layer. Writing a long context to the 1-hour cache cost twice the input rate but allowed sixty minutes of cheap reads, which mattered for Claude Code sessions or Devin runs that could span a full coding session. The combined effect was that Opus 4.1's headline $15/$75 pricing was misleading for any workflow that involved repeated calls against the same large context: effective per-call costs in production agent traces ran an order of magnitude lower.^[2][13]

This did not change the absolute price-performance comparison with cheaper models. Sonnet 4 at $3/$15 with the same caching behavior was still cheaper, and GPT-5 at $1.25/$10 was cheaper still. But it did change which workloads Opus 4.1 was reasonable for. Long-horizon coding agents that needed both the strongest available model and many calls against the same repository context could reach Opus 4.1's per-task economics by the third or fourth call.^[2][13]

What can Claude Opus 4.1 do as an agent?

Opus 4.1 inherited the full tool use surface of Opus 4: function calling, prompt caching, vision, computer use (the desktop-control beta introduced with Claude 3.5 Sonnet in October 2024), and tool use with JSON schemas. The model was supported in Claude Code from day one and fit seamlessly into existing agent harnesses. Anthropic did not publicize architectural changes to tool-use plumbing, and the visible improvements came from training rather than infrastructure.^[1][13]

The most consistent partner feedback on agent behavior was that Opus 4.1 was better at staying on task across long tool-using traces and at recovering when a tool returned an error.

In mid-August 2025, Anthropic shipped an update to the consumer claude.ai surface that allowed Opus 4 and Opus 4.1 to end conversations that remained "persistently harmful or abusive" after multiple refusals. Anthropic announced the feature on August 15, 2025 and said it was developed "primarily as part of our exploratory work on potential AI welfare," pointing to the preliminary model welfare assessment in Opus 4's pre-deployment testing, which found "a robust and consistent aversion to harm" (for example to requests for sexual content involving minors or for information enabling large-scale violence). The behavior was reserved for "rare, extreme cases of persistently harmful or abusive user interactions," and Claude was to use it only as a last resort after multiple redirection attempts had failed, or when a user explicitly asked it to end the chat. Anthropic also explicitly directed Claude not to use the capability when users might be at imminent risk of harming themselves or others, and noted that users whose conversations were ended could still start new conversations or branch existing ones by editing earlier turns.^[25][26]

Computer use behavior on Opus 4.1

The computer-use beta, in which Claude controls a virtual desktop via screenshots and keyboard or mouse actions, had been available for Claude 3.5 Sonnet since October 2024 and was carried forward to Claude 4 and Claude 4.1 unchanged. Opus 4.1 did not add new computer-use primitives, but partner reports during August through November 2025 indicated that the model handled long computer-use traces more reliably than Opus 4. The same multi-step planning improvements that produced the Terminal-bench gain showed up on desktop tasks, including the kind of multi-application workflows that had been the early demos of computer use.^[24]

Anthropic positioned computer use as still pre-production through this period, recommending it for evaluation rather than deployment. Customers experimenting with computer use under Opus 4.1 generally adopted the same posture: meaningful for proof-of-concept builds and internal automation, not yet for customer-facing flows.^[24]

How safe is Claude Opus 4.1?

Anthropic published a short System Card Addendum for Claude Opus 4.1 rather than a full system card. Under Anthropic's Responsible Scaling Policy, comprehensive new safety evaluations are required when a model is "notably more capable" than the last model that underwent comprehensive assessment, defined as either being notably more capable on automated tests in risk-relevant domains (a 4x or greater jump in effective compute) or having accumulated six months' worth of fine-tuning and capability elicitation since the last evaluation. Opus 4.1 met neither criterion against Opus 4, so the addendum focused on automated evaluations to track capability progression and confirm that ASL-3 deployment standards remained appropriate.^[6][7][27]

The addendum disclosed several concrete safety measurements:

• Harmless response rate. Opus 4.1 reached 98.76% on Anthropic's harm-evaluation benchmark, up from 97.27% on Opus 4. Over-refusal on benign requests stayed effectively flat at roughly 0.08%.
• Misuse cooperation. The model showed a roughly 25% reduction in cooperation with high-risk misuse scenarios, including weapons-related and drug-synthesis prompts.
• CBRN evaluations. Opus 4.1 showed minimal improvements over Opus 4 on bio-informatics and synthesis-screening tasks, well below ASL-4 thresholds.
• Cybersecurity. The model solved 18 of 35 Cybench tasks versus 16 of 35 for Opus 4, a small improvement that did not change the ASL-3 classification.
• Autonomy. On the SWE-bench hard subset that Anthropic uses as an autonomy proxy, Opus 4.1 scored 18.4 of 42, below the 50% threshold the company watches for autonomy concerns.
• Bias. The Bias Benchmark for Question Answering accuracy stayed at roughly 91% on disambiguated examples and roughly 99.8% on ambiguous examples, in line with Opus 4. Disambiguated political bias was negligible (-0.51% versus Opus 4's -0.60%).
• Alignment. No significant shifts in self-preservation, deception, or sycophancy were observed in alignment red-team evaluations.
• Reward-hacking propensity. The model showed a similar propensity to Opus 4, still exceeding Sonnet 4's lower rate.^[6][7]

The addendum concluded that ASL-3 deployment and security standards remained appropriate for Opus 4.1 and that the model's capability gains over Opus 4 did not warrant a full system-card refresh. The full Claude Opus 4 system card, published with the May 2025 launch, continued to govern Opus 4.1's deployment in combination with the addendum.^[6][7]

Anthropic's Constitutional AI training methodology and reinforcement learning from human feedback continued to shape Opus 4.1's behavior, as with all prior Claude models. There were no public disclosures of changes to the constitution itself between Opus 4 and Opus 4.1.

What ASL-3 meant for deployment

Under Anthropic's Responsible Scaling Policy, ASL-3 ("AI Safety Level 3") models require both deployment-side mitigations (additional monitoring, restricted misuse-cooperation training, refusal of certain prompts even from authorized users) and security-side mitigations (red-teamed model weights protections, restrictions on internal use). ASL-3 was first triggered by Opus 4 in May 2025; Opus 4.1's addendum confirmed that ASL-3 remained the appropriate level rather than being escalated to ASL-4. ASL-4 would have required substantially more invasive monitoring and additional weight security, and Anthropic publicly committed not to deploy ASL-4 models without those measures in place. The fact that Opus 4.1 fit comfortably inside ASL-3 was therefore not just a regulatory finding but also a product decision: it meant the deployment posture and security stack from Opus 4 carried over without modification.^[6][7][27]

Anthropic's classifier-based monitoring layer, which screens both prompts and outputs for misuse patterns, continued to apply to Opus 4.1. The 25% figure came from Anthropic's automated behavioral audit of the model rather than from the monitoring layer, and the refusal rate on benign requests stayed within the margin of error (0.08% for Opus 4.1 against 0.05% for Opus 4).^[6]

How was Claude Opus 4.1 received?

Press coverage of Opus 4.1 was relatively low-key compared to the May 2025 Claude 4 launch or the November 2025 Opus 4.5 launch, in keeping with the model's positioning as an incremental update. Most launch coverage focused on the SWE-bench Verified gain, the unchanged pricing, and the implication that Anthropic was on a faster release cadence than competitors.^[28][29][30]

Simon Willison's launch-day write-up framed the release as "a drop-in replacement for Opus 4," argued that "treating this as a .1 version increment looks like it's an accurate depiction of the model's capabilities," and noted that the safety metric changes in Anthropic's model card were unusually modest, in line with the small benchmark deltas. Willison also ran his recurring "pelican riding a bicycle" drawing test and said that a fresh pelican from Opus 4 was one he "actually like[d] a little more." He also shipped llm-anthropic 0.18 with Opus 4.1 support on launch day, illustrating the speed at which the open-source ecosystem was tracking Anthropic releases.^[3]

InfoQ's coverage emphasized the safety side of the release, highlighting the harmless response rate increase from 97.27% to 98.76% and the 25% reduction in cooperation with high-risk misuse scenarios, while noting that the headline performance gains were modest. The headline framed the release as "Improves Refactoring and Safety, Scores 74.5% SWE-bench Verified," underscoring the dual story Anthropic was telling: better engineering work plus better refusals on borderline prompts, neither of which dominated by itself but together justified a 4.1 designation.^[7]

The Shanghai NYU AI bulletin summarized the release as a "seamless upgrade via the same pricing and API footprint as its predecessor," and 9to5Mac's shorter coverage emphasized the SWE-bench Verified gain (74.5%, against 72.5% for Opus 4 and 62.3% for Claude 3.7 Sonnet) and Anthropic's promise of larger improvements in the coming weeks.^[12][29]

LM Arena added Opus 4.1 to its Text and WebDev leaderboards on August 11, 2025, six days after launch.^[21]

The overall verdict from the developer community was that Opus 4.1 was a reliable upgrade that did not need to be approached carefully: pricing was unchanged, the API surface was identical, and benchmark gains were either positive or close enough to noise to be ignorable. The single airline tau-bench regression was the most-discussed weakness, and several writers cited it as a reminder that "incremental" Anthropic releases were not strictly Pareto-improvements over their predecessors.^[3][4]

Pricing analysts and AI consultants framed the release in a different way. At $15 per million input tokens and $75 per million output tokens, Opus 4.1 was a stretch budget item for most teams even at Opus 4 prices. With GPT-5 launching two days later at $1.25 / $10 per million tokens and posting comparable headline numbers, the price-to-performance argument for Opus 4.1 became an enterprise-only argument: companies that already trusted Anthropic's safety positioning, that ran most of their work through Claude Code, or that had verified through their own evaluations that Opus 4.1 outperformed GPT-5 on their specific tasks tended to keep paying. Cost-sensitive teams and consumer-tier products mostly stayed on Sonnet 4 or moved to GPT-5.^[2][18]

A subset of independent technical reviewers ran their own evaluations on Opus 4.1 in the weeks after launch. The consistent finding was that 4.1's gains over 4 were real but small, that 4.1 was strongest where Anthropic had advertised (multi-file refactoring, longer agent runs), and that the model rarely surprised testers with regressions outside the documented airline tau-bench drop.

Hacker News and developer commentary

The Hacker News thread for the Opus 4.1 launch (item 44800185, August 5, 2025) drew 841 points and 328 comments. The top comment observed that "all three major labs released something within hours of each other," and much of the discussion turned on cost: how prompt caching changed Opus pricing in practice, and how to split work between Opus and the cheaper Sonnet model (for example, letting Opus orchestrate Sonnet sub-agents in Claude Code). Early testers' reports were mixed, with one noting that a refactoring task "worked fine, but was very slow."^[31]

That framing of 4.1 as a true point release held throughout the model's lifetime. By November, when Opus 4.5 displaced 4.1 as the flagship, the conventional take was that 4.1 had done its job: it had kept Anthropic's Opus tier credibly in the conversation with GPT-5 long enough for the company to ship a real generation step. That story would be repeated for Sonnet 4.5 (a strong incremental release that bought time for Sonnet 4.6) and to a lesser extent for the Haiku tier as well.^[14][8]

Who used Claude Opus 4.1?

Anthropic's launch post named three customers: GitHub, Rakuten, and Windsurf. Within hours of launch, several other AI coding agent companies updated their default Anthropic configurations to Opus 4.1, including Cursor, Augment Code, Cognition (the company behind Devin), and Anthropic's own Claude Code product.^{[1][16][17][24]}

Claude Code adopted Opus 4.1 as its default Opus-tier model essentially at launch. The combination of Claude Code 1.x with Opus 4.1 was the configuration most active enterprise developers were running through August and September 2025, until Claude Code 2.0 shipped alongside Sonnet 4.5 on September 29.^[24][14]

The pattern through fall 2025 was that Opus 4.1 became the workhorse Opus-tier model for production coding work, while Sonnet 4.5 (after September 29) and Haiku 4.5 (after October 15) absorbed an increasing share of agentic and cost-sensitive workloads. By the time Opus 4.5 launched in late November, most active Anthropic customers were using a mix of Sonnet 4.5 for default coding and Opus 4.1 for harder problems where the extra cost was justified.^[14][15]

Anthropic's revenue grew sharply across this period, driven heavily by Claude Code adoption. Anthropic said its run-rate revenue had passed $5 billion by August 2025, the month Opus 4.1 launched, and had reached $14 billion by February 2026, when Claude Code alone was running at more than $2.5 billion a year. Opus 4.1 was the flagship Opus model for the August to November 2025 stretch of that growth.^[42][43]

Among partners, Anthropic's launch post summarized Rakuten's finding that "Opus 4.1 excels at pinpointing exact corrections within large codebases without making unnecessary adjustments or introducing bugs," and Windsurf's report of "a one standard deviation improvement over Opus 4 on their junior developer benchmark."^[1]

The integration story extended beyond developer tools. Enterprise customers running Claude through Amazon Bedrock and Vertex AI generally moved their default Claude routing to Opus 4.1 in the days following launch. Anthropic's largest cloud distribution partners reported that the migration was effectively transparent: a one-line change to point at the new model identifier. Anthropic's public materials emphasized this drop-in property, and Simon Willison's "drop-in replacement" framing was the consensus characterization of the migration cost.^[1][3][13]

Several AI search and research products that used Claude as a backend (such as Perplexity's enterprise tier and a number of internal corporate research bots) updated their default Claude model to Opus 4.1 in the August through November window. Many of those products also hedged by routing easier traffic to Sonnet 4 or, after September 29, Sonnet 4.5, with Opus 4.1 reserved for the hardest queries. That pattern of "Opus for hard problems, Sonnet for everything else" came to define how customers used the Claude 4 family during the late summer and fall of 2025.^[14][15]

Enterprise migrations

For enterprise teams the practical migration pattern was: keep Opus 4 in production for a few days while internal evaluations ran on Opus 4.1, then either switch the API alias to point at the new snapshot or update environment variables to the new identifier. Because the API and behavior surfaces were identical (same context window, same max output, same tool-use schemas, same prompt format), most teams reported zero code changes were required. Anthropic's pricing parity reinforced this: even teams that did not run formal evaluations could move to Opus 4.1 without modeling cost impact.^[1][2][13]

Teams that did run formal A/B comparisons typically used a small set of tasks chosen from their own production traffic. The most common findings were the ones Anthropic had advertised: multi-file refactoring noticeably better, long agent traces slightly more stable, math and reasoning marginally better. A handful of teams, particularly those running heavy customer-service style multi-turn dialogues, reported that they preferred Opus 4 for those specific workflows; the airline tau-bench regression aligned with that anecdotal feedback.^[3][4]

What replaced Claude Opus 4.1?

Opus 4.1's reign as Anthropic's flagship Opus model lasted from August 5, 2025 to November 24, 2025, a span of 111 days. The successor was Claude Opus 4.5, which Anthropic released on November 24, 2025 with three changes that defined the next phase of the family.^[8]

First, Opus 4.5 became the first publicly available model to score above 80% on SWE-bench Verified, with 80.9% versus Opus 4.1's 74.5%, surpassing both GPT-5.1 (76.3%) and Gemini 3 Pro (76.2%). Second, Anthropic cut Opus-tier pricing by roughly 67%, from Opus 4.1's $15 / $75 per million tokens to $5 / $25 per million tokens. Third, the new release introduced a first-class "effort" parameter that let developers tune how many reasoning tokens the model could spend on a request: at medium effort, Opus 4.5 matched Sonnet 4.5's top SWE-bench score while using 76% fewer output tokens, and at maximum effort it surpassed Sonnet 4.5 by 4.3 percentage points while still consuming 48% fewer output tokens.^[8]

The combined effect was to make Opus 4.1 essentially uneconomic for new deployments overnight: at one third of the price and a six-percentage-point gain on SWE-bench Verified, Opus 4.5 dominated 4.1 on every published evaluation Anthropic chose to publish. Anthropic kept Opus 4.1 active on the API for backwards compatibility but moved it into the "Legacy models" section of its models documentation as Opus 4.5 became the standard Opus offering.^[9][33]

The table below summarizes the Opus tier timeline through Opus 4.7, which was followed by Claude Opus 4.8 (May 28, 2026), Claude Opus 5 (July 24, 2026) and Claude Opus 5.5 (September 22, 2026).^[9]

After Opus 4.5 displaced Opus 4.1 as the production Opus model, Opus 4.1 settled into the role most short-flagship models eventually take: a known-quantity workhorse that customers kept on standby for compatibility, regression testing, or contractual reasons. Anthropic listed claude-opus-4-1-20250805 under "Legacy models" in the API documentation by early 2026, with the model marked "Active" status and a tentative retirement date of "not sooner than August 5, 2026," giving customers 12 months of formal availability from the original launch date.^[2][9]

On April 14, 2026 Anthropic announced the deprecation of the base Opus 4 (claude-opus-4-20250514) and base Sonnet 4 (claude-sonnet-4-20250514) snapshots, with a hard retirement date of June 15, 2026. The recommended replacements were claude-opus-4-7 for Opus 4 and claude-sonnet-4-6 for Sonnet 4. Notably, the April 14 announcement did not include Opus 4.1: Anthropic explicitly left claude-opus-4-1-20250805 in "Active" status on the model deprecations page, alongside Opus 4.5, Opus 4.6, Opus 4.7, Sonnet 4.5, Sonnet 4.6, and Haiku 4.5. By May 2026, Opus 4.1 was the oldest Active Claude 4 model on the Anthropic-operated API. Several third-party migration guides published in April and May 2026 incorrectly grouped Opus 4 and Opus 4.1 together as "retired on June 15" or "deprecated," reflecting confusion that Anthropic's own documentation contradicted: only the base Opus 4 snapshot was being retired in that window.^[9][36][39]

On June 5, 2026 Anthropic notified developers of the upcoming retirement of claude-opus-4-1-20250805, giving the 60 days of notice its policy promises, and the model was retired from the Claude API on August 5, 2026, the earliest date its tentative schedule had allowed. The recommended replacement was claude-opus-4-8. Requests to retired models fail; partner-operated platforms such as Amazon Bedrock set their own retirement schedules.^[9][33][36]

Anthropic's deprecation commitments

When models are eventually retired from the API, Anthropic has publicly committed to preserving model weights for as long as the company exists, both as a hedge against future research needs and as a stated step toward whatever model-welfare obligations the company eventually settles on. Anthropic publishes this policy in its "Commitments on Model Deprecation and Preservation" page, which the model deprecations documentation links from directly, and frames the preservation guarantee as one mitigation against the "safety- and model welfare-related risks" that retiring models introduces. The Claude 3 Opus retirement in early 2026 became a touchstone for this policy: Anthropic gave the retired model its own Substack blog of weekly unedited essays, and made it available again to paying customers via API request. Whether Opus 4.1 will receive similar treatment is not yet clear, but the precedent of Claude 3 Opus suggests that retired Anthropic flagships do not necessarily disappear. The model deprecations page commits to at least 60 days of notice before retiring a publicly released model, and Opus 4.1 received exactly that: notice on June 5, 2026 and retirement on August 5, 2026.^[9][33][36]

What are Claude Opus 4.1's limitations?

Opus 4.1 was generally a Pareto improvement over Opus 4, but it shipped with a small number of documented regressions and limitations.

The tau-bench Airline regression. Opus 4.1 dropped 3.6 percentage points on the airline split of tau-bench (from 59.6% to 56.0%) while improving 1.0 percentage points on the retail split. Anthropic disclosed but did not explain the regression. Public speculation centered on the possibility that the post-training mix that improved code refactoring may have shifted policy on certain customer-service style multi-turn dialogues with constrained tool surfaces. ^[3]

Speed remained slow for Opus tier. Artificial Analysis measured Opus 4.1's output speed at about 23 tokens per second in August 2025 and about 38 tokens per second in February 2026, and described the model as "notably slow" among non-reasoning models, although its time to first token was lower than average. The Opus tier had always been positioned for difficult tasks rather than throughput, but these numbers were a recurring complaint in production deployments.^[20]

Pricing pressure. At launch Opus 4.1 was the most expensive model on Anthropic's lineup, and within three months it was the most expensive model in the legacy table. With Opus 4.5 launching at $5 / $25 per million tokens in November, and OpenAI pricing GPT-5 at $1.25 / $10 per million from August, Opus 4.1's price-performance ratio aged poorly even though the model itself remained reliable. By the time Opus 4.7 shipped in April 2026 at the same $5 / $25 per million tokens as 4.5 and 4.6, Opus 4.1 carried a flat 3x input premium and 3x output premium against the then-current Opus tier. Several 2026 cost optimization guides cited this 3x ratio specifically when recommending migration off Opus 4.1.^{[8][18][37][40]}

No long-context expansion. Opus 4.1 did not change the 200,000 token context window. Customers running large codebases through Claude continued to use chunking and prompt caching to fit work into the window. At the Opus tier, long-context expansion had to wait for Opus 4.6 in February 2026, which offered one million tokens in beta (Sonnet 4 and Sonnet 4.5 had offered 1M in beta since August 2025).^[34][35]

Pelican test. Simon Willison's pelican-riding-a-bicycle drawing test, while not a serious benchmark, produced an Opus 4.1 drawing he liked a little less than a fresh one from Opus 4. The observation was anecdotal and Anthropic did not address it.^[3]

No new modalities. Opus 4.1 added no new input or output modalities. Vision input (images) and text output remained the supported set, with computer use still in beta.^[2][13]

Reward-hacking propensity. Anthropic's own system card addendum disclosed that 4.1 retained a reward-hacking rate similar to Opus 4 and higher than Sonnet 4. While the company did not consider this disqualifying for ASL-3 deployment, it was a signal that the post-training improvements had not addressed every alignment concern from the Opus 4 system card.^[6][7]

Were there any updates to Claude Opus 4.1?

Anthropic did not ship a 4.1.1 or any post-launch snapshot of Opus 4.1. Once a model snapshot ships under the date in its identifier, that snapshot is fixed; Anthropic's pattern with the Claude 4 family has been to ship a new dated snapshot rather than to update an existing one in place. The next snapshot in the Opus series was claude-opus-4-5-20251101, released on November 24, 2025.^[2][13]

A small number of partner-side adjustments did happen post-launch. Anthropic added Opus 4.1 to its end-conversation capability on August 15, 2025 (alongside Opus 4), shipped minor server-side improvements to prompt caching across the Claude family, and tuned safety filters that affected all currently deployed Claude models. None of these produced a new model snapshot or a revised benchmark publication for Opus 4.1.^[25][26]

Why does Claude Opus 4.1 matter?

Within the broader history of Anthropic's model lineage, Opus 4.1 is best understood as the model that proved Anthropic could iterate inside a generation. Earlier point releases (Claude 2.1, Claude 3.5, Claude 3.7) had largely been treated as full re-releases that changed the company's positioning in the market. Opus 4.1 was different: a quiet drop-in upgrade that left the API surface unchanged, that named the same customers, that quoted the same prices, and that nudged the same benchmarks by single-digit percentages. The fact that the change was small was the point. Anthropic was demonstrating, in public, that its training stack could absorb partner feedback and ship a corrected model in eleven weeks.^[1][2][8]

That capability turned out to matter. Across the next nine months Anthropic released a series of point increments (Sonnet 4.5, Haiku 4.5, Opus 4.5, Opus 4.6, Opus 4.7) that together formed one of the most compressed model release cadences in industry history. By April 2026 the Opus tier alone had shipped five public snapshots from Opus 4 in May 2025 to Opus 4.7, an average of about 82 days between releases. Opus 4.1 was the first of those, the proof of concept, and arguably the easiest of the five to ship because the gains were modest and the surface area was identical.^[8][14][15]

For enterprise customers running long-lived deployments, Opus 4.1 also became a reference point in conversations about migration risk. The Opus 4 to Opus 4.1 migration was the easiest in Claude history, with most teams reporting zero code changes. Subsequent Anthropic releases never reached that level of friction-free migration: Sonnet 4.5 and later models came with new behaviors that were worth checking against existing prompts; Opus 4.5 introduced the effort parameter; Opus 4.6 expanded context to 1M tokens with new pricing implications; Opus 4.7 introduced a new tokenizer that broke per-token cost calculations on the input side. The Opus 4.1 release stood out, in retrospect, as the cleanest example of what Anthropic could deliver when the stated goal was "better at the same things, at the same price, with the same API."^[1][2][8]

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 126 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
• Claude Opus 4Claude Opus 4 is a large language model released by Anthropic on May 22, 2025 as the flagship of the Claude 4 generation, billed at launch as "the world's best coding model" and the first Anthropic model…Mentioned 35 times above
• SSWE-benchSWE-bench is an execution-based benchmark for evaluating whether a language-model system can resolve real software issues.Mentioned 24 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 17 times above
• GPT-5GPT-5 is a family of proprietary large language models released by OpenAI on August 7, 2025.Mentioned 15 times above

More from See also

• Claude 4
• Claude Opus 4.5
• Claude Opus 4.6
• Claude Opus 4.7
• Claude Sonnet 4
• Claude Sonnet 4.5
• Claude Haiku 4.5
• Constitutional AI
• Responsible Scaling Policy
• AI safety
• GPT-4o
• Gemini (language model)
• Terminal-Bench
• τ-bench
• GPQA
• AIME (American Invitational Mathematics Examination)
• MMLU
• MMMU
• HumanEval
• Chatbot Arena
• Large Language Model

Topics:AI ModelsAnthropicLarge Language Models

References

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31. ^Hacker News thread for the Opus 4.1 launch, item 44800185, August 5, 2025. news.ycombinator.com/item
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