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Anthropic released Claude Sonnet 5.5, replacing Sonnet 5 as its medium-sized model, a week after debuting Opus 5.5. The company says the new model runs over 30% faster and uses fewer tokens while keeping Sonnet 5's pricing of $2 per million input tokens and $10 per million output tokens. Sonnet 5.5 is also the first Sonnet-tier model to ship with cybersecurity safeguards similar to those used in Anthropic's top-tier Opus models.
Anthropic launched Sonnet 5.5, a faster and lower-cost model that it says outperforms its predecessor at coding, task completion and document creation. The release follows last week's launch of the pricier Opus 5.5, with a cheaper Haiku 5.5 model still to come. Anthropic said Sonnet 5.5 does not push the frontier of model capability, but includes improved cybersecurity safeguards compared to earlier Sonnet versions.
Anthropic has released Sonnet 5.5, an update to its mid-tier AI model that the company says runs 30 percent faster than its predecessor and burns tokens more slowly, cutting costs. Anthropic says the model outperforms its more powerful Opus 5.5 on agentic coding benchmarks and now carries cyber capabilities strong enough to trigger the same safeguards applied to its Fable and Opus models. The company also says a refreshed version of Haiku, its smallest model, is coming in the next few weeks.
Anthropic released Claude Sonnet 5.5, the second model in its Claude 5.5 lineup after Opus 5.5. The company says it runs over 30% faster and costs up to 30% less per task than Sonnet 5, while keeping the same per-token pricing, and jumps from 10.3% to 70.6% on the Terminal-Bench 4.0 agentic coding evaluation. A third model, Claude Haiku 5.5, is planned for release in the coming weeks.
Anthropic released documentation detailing how to prompt its Claude Opus 5.5 model, highlighting behavioral differences from Claude Opus 5 including effort calibration, thinking behavior, and handling of unattended multiagent tasks. The guide notes Opus 5.5 generates output over 30% faster than its predecessor while typically using fewer tokens to complete the same task, and that existing Opus 5 prompts should still work without modification.
A writer describes rebuilding their personal homepage entirely through Claude, without writing or running code or opening a GitHub pull request, using Opus 5.5 in a Claude Project. Roughly 60 parallel Claude sessions handled tasks including a CGI parody video and an original soundtrack, with most orchestration done from a phone rather than a local machine.
Andrew Boyd, founder of Standard Agents Inc., says his Jev decision model beat Pokémon Red's Elite Four and Champion, reaching the Hall of Fame on September 23, 2026, less than a week after the run began. Jev isn't a chatbot or LLM; it picks from lists of weighted options rather than reading the screen, while Anthropic's Claude Opus 5 monitored the game log and adjusted those options to help it when stuck. A harness changelog logged 474 fixes, including repeated failures like walking into a shut door 53 times and looping a ladder 124 times.
Benchmarking site Arena analyzed high-reasoning Text Arena responses from August and September 2026 and found Anthropic's Claude Opus 5.5 uses far fewer em dashes and semicolons than Opus 5, along with shorter, simpler sentences. Em dash usage fell from 15.2 to 0.8 per 1,000 words, and average sentence length dropped from 12.14 to 10.03 words, though overall answers grew longer, from 453 to 481 words on average.
Developer Carter Leffen used OpenAI's Astra model to locate and decrypt an Enigma-encoded message that had remained unsolved since 2005, with the model conducting its own archival research and building a simulator of the Enigma machine. Cryptology researcher Frode Weirerud, who maintains a database of unbroken Enigma messages, independently verified the solution and called it 'awe' inspiring. Anthropic's Opus model reportedly cracked a separate long-unsolved message as well.
Meta's personal AI agent Muse is reportedly growing faster than ChatGPT did in its early days, and the company plans to bring it to smart glasses and a small Tamagotchi-style device. The news came during a busy week for AI model releases, with Anthropic launching Opus 5.5 and OpenAI following with GPT-6 updates roughly 90 minutes later.
A developer built a single-agent system on OpenComputer that uses Anthropic's Claude Opus 5.5 to turn a webpage's content into an explainer video without any traditional video-generation model. The system fetches page data, runs the rendered page in a disposable microVM with a virtualized clock for deterministic frame capture, and encodes frames into an MP4 via ffmpeg, storing the result as a public Vercel Blob URL.
A researcher describes early experiments using the newly released GPT-6 Sol and Opus 5.5 models to go beyond routine transcription work and attempt to actually solve open historical problems, including tracing alchemical knowledge and decoding 17th century letters. The author outlines criteria for which historical puzzles are 'tractable' for AI, such as codebreaking tasks, citing an example of an AI model decrypting a 1941 German army communication.