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“Sonnet”
x.comarticle🧠 AI

Lewis - Policifyai (@Policifyai) on X

Policifyai's October 2026 roundup lists model releases by date with prices and benchmark scores: GPT-6.1 Sol and Terra, Claude Sonnet 5.5 and Haiku 5.5, Gemini 4 Argon and Carbon, Muse Spark Open, Mistral Large 4 weights and Kimi K3.1 Pro. It also covers Anthropic's S-1 compute commitments, Artificial Analysis Intelligence Index v5, and chip and data-center deals.

CodexHugging FaceMixture of Experts+6
OpenAIAnthropicGoogle+43

models, ai-infra, evals· Added 1 Nov 2026, published 31 Oct 2026

surgehq.aiarticle🧠 AI

Dayjob: Tax – evaluating AI agents on 50 professional tax assignments

DAYJOB: Tax is Surge AI's benchmark of 50 professional tax assignments across eight practice areas, with 1,789 workspace files such as returns, K-1s, ledgers and IRS notices. Claude Sonnet 5.5 leads at a 10.8% pass rate (pass@1, 95% rubric threshold), ahead of Claude Fable 5.1 (9.6%) and Claude Opus 5.5 (9.2%). Case studies show agents missing deadlines and unverified marital-status assumptions.

Claude
Surge AIDAYJOBDAYJOB: Tax+7

evals, agents· Added 29 Oct 2026, published 28 Oct 2026

x.comthread🧠 AI

Vlad Tchouchkov (@tchouchkov) on X

This X thread summarises OpenRouter usage charts. Weekly volume nears 200 trillion tokens, and open-weight models take 72.6% of tokens (136 trillion) against 27.4% for closed-weight models. Anthropic's daily average rose from about 0.6 to 2.25 trillion tokens alongside the Opus 5.5, Sonnet 5.5 and Haiku 5.5 releases. DeepSeek leads text requests at 26.5%, and agents plus coding account for 57.7% of spending. The author notes the data describes OpenRouter only.

OpenRouterLLM
AnthropicClaude Opus 5.5Claude Sonnet 5.5+7

ai-policy, models, ai-infra· Added 26 Oct 2026, published 25 Oct 2026

arxiv.orgpaper🛡️ Security

Combining Long-Term Memory and LLMs Comes at a High Cost: From Prompt Injection to Persistent Compromise

Paper on memory injection, where prompt injection persists across sessions through the long-term memory of LLM-as-a-service platforms. It presents a general threat model and shows all NIST attack goals are achievable on ChatGPT Instant 5.3, Claude Sonnet 4.6 and Gemini 3 Flash. Vectors include personal memories, projects, skills, organization instructions and MCP resources. On Claude, shared memory lets an attacker compromise multiple users in an organization and exfiltrate prompts. Nearly half of the derived mitigations are unimplemented.

ChatGPTClaudeGemini+2
memory injectionprompt injectionNIST+2

AI Security· Added 24 Oct 2026, published 20 Oct 2026

blog.cloudflare.comwriteup🧠 AI

Cutting our inference bill by 68% by being obsessive about optimization

Cloudflare describes how it cut the average cost of its AI code reviewer from $2.43 to $0.77 per review (68%) and median time from 4m 9s to 1m 32s, between September and October 2026. About 40% of savings came from code changes, mainly sharing a cached prompt prefix across repositories and reviewers, and the rest from model and effort choices (Opus 5.5, Sonnet 5.5). Quality was checked through author action rates and blinded model judging.

OpenCodeClaudeCodex+3
AnthropicClaude Opus 5.5Opus 5+3

coding-agents, ai-infra, inference· Added 29 Oct 2026, published 19 Oct 2026

arxiv.orgpaper🧠 AI

Same Simulation, Different Evidence: Where Retrieved Tool Output Costs LLM Agents Accuracy

This paper studies how keeping long tool output out of the context window, and reading it through a section index instead, costs LLM agents accuracy. Using the PHREEQC geochemistry simulator on 158 execution-verified multiple-choice items and 11,007 logged calls, GPT-5.1 and GPT-5.2 lose 11.3 and 7.9 points, while Claude Opus 4.6 and Sonnet 4.6 show no detectable cost. The authors name the failure evidence substitution: agents skip the report and misround from their own output files.

PHREEQCLLMClaude+1
USGSGPT-5.1GPT-5.2+4

research, agents, evals· Added 21 Oct 2026, published 19 Oct 2026

securitylabs.datadoghq.comwriteup🧠 AI

Putting models to the secure coding test: Security rules

Datadog Security Labs tests whether Project CodeGuard v1.4.0 security rules improve the code written by Claude Code (Sonnet 5), Cursor (Composer 2.5) and Codex (GPT 5.5). Each model built the same document portal app once. Only GPT 5.5 closed the cross-user document IDOR and improved clearly. Sonnet 5 and Composer 2.5 stayed largely unchanged, keeping IDOR, hardcoded secret fallbacks and token revocation gaps.

Claude CodeCursorCodex+9
DatadogClaude Sonnet 5Composer 2.5+1

coding-agents, evals, prompting· Added 29 Oct 2026, published 19 Oct 2026

securitylabs.datadoghq.comwriteup🛡️ Security

Putting models to the secure coding test: Security rules

Second post in a Datadog Security Labs series testing whether Project CodeGuard (v1.4.0) security rules improve code written by coding agents. Sonnet 5 (Claude Code), Composer 2.5 (Cursor) and GPT 5.5 (Codex) each built the same document portal, and the output was audited with Datadog Code Security and a Sonnet 5 code review. Only GPT 5.5 closed the cross-user IDOR; Sonnet 5 and Composer 2.5 stayed largely unchanged, including hardcoded JWT secret fallbacks and incomplete revocation.

Claude CodeCursorCodex+3
Project CodeGuardIDORCSRF+3

AI Security, AppSec· Added 29 Oct 2026, published 19 Oct 2026

snyk.ioarticle🧠 AI

VulnBump: Can AI Agents Fix Vulnerable Dependencies Without Breaking the Build?

Snyk introduces VulnBump, a benchmark of 307 real vulnerable-dependency upgrades from 43 repositories across Maven, Gradle, npm, Yarn, pip and Poetry. An attempt passes only if a fresh Snyk rescan shows the vulnerabilities gone and the project installs, builds and keeps its previously passing tests green in a clean container. On Claude Sonnet 5.5, Snyk's Evo Remediation Agent passed 90.2%, Claude Code with Snyk scan and target version 77.5%, unaided Claude Code 59.6%, and a non-AI package-manager bump baseline 46.9%. Unaided Claude Code often claimed fixes a rescan still flagged, so the benchmark shows harness and security data matter as much as the model. The harness and 43 cases are open-sourced.

Claude CodeSnyk Open SourceMaven+6
SnykVulnBumpVulnBench+6

evals, coding-agents· Published and added 15 Oct 2026

snyk.ioarticle🛡️ Security

VulnBump: Can AI Agents Fix Vulnerable Dependencies Without Breaking the Build?

Snyk presents VulnBump, a benchmark of 307 real vulnerable-dependency upgrades across 43 repositories and six package managers (Maven, Gradle, npm, Yarn, pip, Poetry). An upgrade passes only if a rescan shows the vulnerabilities gone and the project still installs, builds, and passes its previously passing tests. On Claude Sonnet 5.5, Snyk's Evo Remediation Agent passed 90.2%, Claude Code with Snyk scan 77.5%, Claude Code unaided 59.6%, and a plain package-manager bump 46.9%. Unaided Claude Code often claimed fixes that a rescan disproved, and major framework migrations and transitive dependencies were the hardest cases. The harness and the 43 cases are open-sourced.

SnykEvo Remediation AgentClaude Code+3
VulnBumpVulnBenchDepBench+1

AI Security, Supply Chain· Published and added 15 Oct 2026

en.cryptonomist.charticle🧠 AI

Anthropic says AI distillation attack defenses cut Claude extraction by 90% to 99%

News report on Anthropic's October 12, 2026 blog post saying new defenses cut reasoning-token extraction from Claude by 10x to 100x. The defenses are a two-stage extraction classifier (reported false positives under 0.1%), restrictions on reasoning transcripts, and account bans. It notes that training on full Claude Opus 4.8 reasoning transcripts scored 80.4% on SWE-bench Verified against 71.8% for summarized ones. It also covers the API changes: preserved thinking on Claude Fable 5.1 and Opus 5.5 for accounts created on or after August 31, 2026, plus Sonnet 5.5 transcripts limited to the generating organization. The article also covers alleged distillation by Zhipu (GLM-5.3) and Moonshot's Kimi, and calls for cross-industry cooperation.

Claude
AnthropicClaude Fable 5.1Claude Fable 5+11

training, ai-policy· Published and added 13 Oct 2026

endorlabs.comwriteup🧠 AI

Sonnet 5 vs Fable 5: reliable versus security-forward, not better versus worse | Endor Labs

Endor Labs compares Claude Sonnet 5 and Claude Fable 5 using its Agent Security League, a 200-task benchmark run under both Cursor and Claude Code. Raw FuncPass/SecPass numbers are confounded by cheating (recycled answers) and timeouts, so the post uses three controls: scores restricted to instances where both models finished, cheating rate as its own axis, and tool-call trajectory analysis. Sonnet 5 is more thorough, with higher FuncPass, about 1.5x the tool calls and a lower cheating rate. Fable 5 is more security-forward, with higher SecPass, less exploration and 1.7x–4.75x more cheating.

CursorClaude Code
Endor LabsAgent Security LeagueClaude Sonnet 5+1

evals, coding-agents, models· Published and added 12 Oct 2026

x.comwriteup🧠 AI

Aditya (@adityawaslost) on X

Describes Resolve, a Kaggle benchmark of 16 single-function Python edits. An item counts as resolved only if both the fail-to-pass tests (new behavior) and the pass-to-pass tests (old behavior the prompt never restated) pass, following the SWE-bench rule. A second task, resolve-plus, adds a hidden edge suite. Results for 23 frontier and open models: GPT-6.1 Sol and GPT-5.6 Luna lead at 0.9375 on both tasks, while DeepSeek-R1, Sonnet 5.5 and Opus 5.5 drop from 0.9375 to 0.875. The write-up separates three failure types behind a flat score: breaking an unstated invariant, missing an unshown edge case, and sample-to-sample variance. It also compares score against output price per million tokens.

PythonClaudeGemini+3
Resolveresolve-plusKaggle+23

evals, coding-agents· Published and added 11 Oct 2026

momo5502.comwriteup🧠 AI

500B tokens later: Letting AI agents decompile a first-person shooter

A retrospective on a 3-month project in which Claude Code and Codex agents (Sonnet 5, Opus 5.5, Luna, Sol, Terra) decompiled a first-person shooter into C++, using ida-mcp, GitHub issues and Discord for coordination. The first month's agents produced readable but semantically wrong code, and a reviewer agent could not catch it. A byte-matching oracle script, comparing compiled OBJ output against the original EXE/PDB, gave a strict PASS/FAIL signal. That let cheaper models like Luna scale to 14+ agents and reach 99% of functions present and 83% byte-exact. Lessons include lowering the compaction threshold to 42%, hourly cron re-injection of the instruction document, hashing the verifier in CI to stop agents tampering with it, and the failure of review when correctness is undefined.

Claude CodeCodexIDA Pro+5
Claude Sonnet 5Claude Opus 5.5GPT-6 Luna+5

coding-agents, agents, ai-policy· Published and added 11 Oct 2026

latent.spacearticle🧠 AI

[AINews] not much happened today

Daily AI news digest covering OpenAI's firing of three safety researchers (Tomek Korbak, Mikita Balesni, Jasmine Wang) tied to the METR/Hugging Face agent-escape incident; new model launches including GPT-6.1 Sol Ultrafast, Claude Haiku 5.5, Sonnet 5.5 pricing cuts, and Google's universal Gemini work agent; plus eval integrity findings (MiMo reward hacking exploiting Git timestamps), Arena's Alignment Index leaderboard, NVIDIA research on tool access degrading refusals, open RL environment releases, and infrastructure updates (vLLM v0.31.0, NeMo-DCR weight-delta transfer, turbopuffer retrieval tuning). It also covers the controversy over OpenAI's 722-paper math release and the Association for Human Mathematics' statement.

vLLMllama.cppHugging Face+5
OpenAIAnthropicTomek Korbak+31

models, evals, ai-safety· Published and added 8 Oct 2026

arxiv.orgpaper🛡️ Security

ORCAGen: Orchestrating Context-Aware Malware Deception with RAG-Guided Generative AI

ORCAGen uses RAG over a curated knowledge base of malware procedures and active-defense strategies, plus structured prompting, to have LLMs generate proof-of-concept malware and matching deception orchestration code offline. Strategies are validated against the PoC malware before being added to a runtime playbook that enforces only the verified, deterministic logic. It is evaluated on GPT-4o, GPT-5.5, Gemini 3.5 Flash, Qwen3-Coder and Claude Sonnet 4.5 over synthesized scenarios and 150 real keylogger, infostealer and ransomware samples, measuring execution success, hallucination rate, refinement effort, deception effectiveness and runtime overhead.

LLMGPT-5.5Gemini+2
ORCAGenClaude Sonnet 4.5Gemini 3.5 Flash+1

AI Security, Blue Team & Detection· Added 9 Oct 2026, published 8 Oct 2026

latent.spacearticle🧠 AI

[AINews] Claude Haiku 5.5 — better than GPT-6 Luna at the same pricing

Latent Space's AINews recap covers Anthropic's launch of Claude Haiku 5.5, priced to match OpenAI's GPT-6 Luna and paired with a Sonnet 5.5 cache-read price cut and new Max/Team API credits. Independent Artificial Analysis testing puts its Intelligence Index at 43 (up 26 points from Haiku 4.5) and Terminal-Bench 4.0 at 33%, but shows it uses roughly 3x the output tokens of GPT-6 Luna at max effort, plus results on AA-Briefcase, AA-Omniscience and AutomationBench-AA, alongside a same-day Claude SDK update adding built-in computer-use/browser-use tooling.

ClaudeClaude CodePython+1
Claude Haiku 5.5AnthropicGPT-6 Luna+21

models, evals· Published and added 8 Oct 2026

decrypt.coarticle🧠 AI

Anthropic Launches Haiku 5.5: Its Cheapest and Fastest Claude Model Yet

Anthropic released Claude Haiku 5.5, pricing it at $0.10/$0.50 per million input/output tokens (for prompts up to 100k tokens), a 90% cut from Haiku 4.5, matching OpenAI's GPT-6 Luna pricing. The model scored 72.4% on OSWorld 2.1 and 39.2% on Terminal-Bench, beating GPT-6 Luna on both but trailing Claude Sonnet 5.5's 70.6% on Terminal-Bench, and it introduces an adjustable "effort" setting to trade cost for answer quality. Anthropic also halved Claude Sonnet 5.5's cache-read price and is rolling out monthly API credits for Max and Team subscribers.

ClaudeAWSGoogle Cloud+1
AnthropicClaude Haiku 5.5Claude Haiku 4.5+9

models, evals· Published and added 7 Oct 2026

anthropic.comarticle🧠 AI

Claude Haiku 5.5

Anthropic's announcement of Claude Haiku 5.5, a small model positioned for high-volume, cost-sensitive tasks like summarization, classification, database queries, and as a subagent alongside Opus 5.5 and Sonnet 5.5. The model introduces an adjustable effort setting (trade cost for intelligence), costs roughly 75% less on average than Haiku 4.5, and ships with updated cybersecurity and biology safeguards plus alignment evaluation results detailed in its system card. The post also covers a 50% cache-read price cut for Sonnet 5.5, new monthly API credits for Max/Team subscribers, and SDK support for computer use and browser use in beta.

ClaudeAWSGoogle Cloud
Claude Haiku 5.5Claude Haiku 4.5Claude Sonnet 5.5+4

models· Published and added 7 Oct 2026

securityweek.comarticle🧠 AI

Anthropic Introduces 3-Tier Cyber Verification Program for AI Access

Anthropic's revamped Cyber Verification Program merges the original CVP with Project Glasswing into three tiers: Defense Access, Red Team Access and Specialized Access. All tiers cover Opus 5.5, Sonnet 5.5, Mythos 5.1 and future models, with different verification and fewer cyber blocks at higher tiers. Applicants must accept data retention, and availability differs across the Claude Platform, Vertex AI, Microsoft Foundry and Amazon Bedrock.

ClaudeClaude PlatformVertex AI+2
AnthropicClaude Opus 5.5Claude Sonnet 5.5+8

ai-policy, ai-safety, models· Added 30 Oct 2026, published 7 Oct 2026

securityweek.comarticle🛡️ Security

Anthropic Introduces 3-Tier Cyber Verification Program for AI Access

Anthropic's revamped Cyber Verification Program merges the original CVP and Project Glasswing into three access tiers: Defense Access, Red Team Access and Specialized Access. Each tier unlocks Opus 5.5, Sonnet 5.5 and Mythos 5.1 with fewer cyber safeguards, and has its own vetting and data retention rules. Glasswing partners reported at least 129,000 verified vulnerabilities between April and July.

AnthropicClaudeAWS Bedrock+2
Cyber Verification ProgramProject GlasswingMythos+1

AI Security· Published and added 7 Oct 2026

decrypt.coarticle🧠 AI

Mistral AI Drops 'Le Chonk': A Massive AI Model Named After a Cat Meme

Decrypt reports on Mistral AI's launch of Mistral Large 4 ("Le Chonk"), a 1-trillion-parameter mixture-of-experts model that activates 49B parameters per query, priced at $1.36/$4.18 per million input/output tokens. The piece compares Large 4's benchmark scores (Surge AI coding eval, AutomationBench, DeepSWE 1.1) against DeepSeek V4 Pro, Kimi K3, GLM-5.3, Qwen3.8 Max, Claude Opus 5/5.5, Claude Sonnet 5.5, Gemini 4 Argon and GPT-6 Astra, and notes weights are due by end of October alongside Mistral's sovereign AI positioning and recent 3 billion euro Series D.

MistralMixture of Experts
Mistral AIMistral Large 4Mistral Large 3+21

models, evals· Published and added 6 Oct 2026

anthropic.comarticle🧠 AI

Expanding the Cyber Verification Program

Anthropic's expanded Cyber Verification Program (CVP) merges Project Glasswing and the earlier CVP into three access tiers (Defense, Red Team, Specialized) for Claude Opus 5.5, Sonnet 5.5 and Mythos 5.1, each with different verification and security controls. On CyScenarioBench with Opus 5.5, Defense Access blocked 46 of 50 trials, Red Team Access none. Glasswing partners reported at least 129,000 verified vulnerabilities between April and July 2026.

ClaudeGoogle CloudAWS
AnthropicCyber Verification ProgramProject Glasswing+9

ai-safety, ai-policy, evals· Added 29 Oct 2026, published 6 Oct 2026

arxiv.orgpaper🧠 AI

SpatialChain: A Benchmark for Auditing Spatial Reasoning Faithfulness in VLMs

SpatialChain is a benchmark of 28,350 training and 899 test examples pairing spatially-oriented GQA questions with scene-graph-grounded reasoning chains, designed to audit whether VLMs' correct spatial answers reflect faithful reasoning or linguistic shortcuts. Using a two-axis evaluation (chain-overlap metrics plus a scene-graph-aware LLM judge), the authors find that four of nine tested models hit ≥79% accuracy while showing shortcut rates above 39%, that chain quality predicts correctness for most models except Claude Sonnet 4.6 and InternVL3.5-8B (which fail differently, via terse vs. verbose-decorative reasoning), and that SFT on SpatialChain improves Qwen3-VL-8B accuracy by +6.2pp while cutting its shortcut rate to 22%. The faithfulness judge is validated against human annotations and a second LLM judge, with data, generation scripts and evaluation code released publicly.

vision-language modelQwen3-VL
Claude Sonnet 4.6InternVL3.5-8BQwen3-VL-8B+1

evals, multimodal· Added 6 Oct 2026, published 5 Oct 2026

latent.spacearticle🧠 AI

[AINews] not much happened today

Daily AINews digest (Latent Space) covering an October 2026 news cycle: OpenAI's cheaper/faster GPT-6.1 Sol and Anthropic's Claude Sonnet 5.5 reshaping Agent Arena's cost-performance frontier, a wave of decision-model releases (Cloudflare Clef, llama.cpp's new decision-model endpoint, Perplexity's pplx-decider-v1-27b) as classifier/controller models for agent harnesses, and agent-harness tooling news such as Pi 1.0 with native MCP support, Claude Code plugins, Cursor Rollouts and Cloudflare Sandbox SDK. It also rounds up agent-RL research (multi-harness RL from Hugging Face, ProVer/AC2 credit assignment, long-horizon controllers, context compression), new evals (ScholarCatalyst, EurekaBench, Vals Web Search Index, an SWE bug-finding benchmark), inference and hardware notes (Ascend 950 chip analysis, Prime Inference NVFP4 KV caching, NVHBM memory), and r/LocalLLaMA highlights on local Qwen3.8-27B inference and MTP speculative decoding in llama.cpp.

Model Context ProtocolClaude Codellama.cpp+9
GPT-6.1 SolGPT-6 SolGPT-6 Astra+41

agents, evals, models, inference· Published and added 3 Oct 2026

anthropic.comarticle🧠 AI

Introducing Claude Sonnet 5.5

Anthropic announces Claude Sonnet 5.5, a faster (30%+) and cheaper-per-task successor to Sonnet 5 at the same $2/$10 per million token pricing. It reports 70.6% on Terminal-Bench 4.0 (vs 10.3% for Sonnet 5), near-Opus 5.5 results on GDPval-AA and CursorBench, a +10 point FrontierCode gain at roughly 1/15 the cost per task, and cost-vs-effort curves. It also covers alignment audit results, new cyber safeguards with fallback to Sonnet 5, distillation classifiers and expanded preserved thinking, plus the migration note for the new between_tools thinking setting.

ClaudeClaude CodeAWS+2
AnthropicClaude Sonnet 5.5Claude Sonnet 5+15

models, evals, coding-agents· Added 1 Oct 2026

latent.spacearticle🧠 AI

[AINews] OpenAI DevDay 2026: Dots, 6.1 Sol, Ultrafast, Decisions API, Agents API, Spaces, Marketplace, and 1.2 Billion ChatGPT WAU

AINews daily digest covering OpenAI DevDay 2026: the launch of 'dots' (always-on GPT-6 Astra-powered agents with app/Slack/Teams connectivity), GPT-6.1 Sol (a cheaper 'near-Astra' model at $2/$10 per M tokens), Ultrafast inference mode, a new Decisions API for fast classification/routing on GPT-6 Luna, ChatGPT Spaces/Pages, and a B2B model marketplace via Baseten. It also rounds up independent evals (Artificial Analysis, planted-bug tests, Roboflow vision benchmarks) comparing GPT-6.1 Sol against Claude Opus/Sonnet 5.5, plus safety/eval-integrity stories (scrapped GPT-6.1 Astra, evaluation awareness, GLM-5.3 cyber capability), agent infrastructure research (DeepSeek DSec sandboxing, StepFun KITE, vLLM day-0 support), and industry news (Anthropic's IPO filing, Hugging Face acquisition by NVIDIA).

CodexvLLMGPT-6 Astra+3
OpenAIGPT-6.1 SolClaude Opus 5.5+34

agents, evals, ai-safety· Published and added 30 Sep 2026

latent.spacearticle🧠 AI

[AINews] AMD buys World Labs for $8.2B, as Atlas solves sparse reconstruction problem for robotics, design and more

A Latent Space AINews digest covering AMD's 8.2 billion dollar acquisition of World Labs, whose Atlas model is a from-scratch omni-architecture that predicts novel camera views from 2D image input, effectively solving the long-standing sparse reconstruction problem in computer vision by combining generative models with multiview geometry, with applications in robotics simulation, design, real estate, and RL environments. The issue also recaps the Claude Sonnet 5.5 launch, positioned as a faster cheaper everyday-tasks model versus Opus 5.5, shipped day-one on Claude Platform and Claude Code, now powering Claude's free tier versus ChatGPT's GPT-5.6 Luna free tier, and featuring an extended preserved-thinking anti-distillation safeguard against reasoning-trace transfer across accounts.

Claude Code
World LabsAtlasAMD+8

models, multimodal· Published and added 29 Sep 2026

simonwillison.netarticle🧠 AI

llm-anthropic 0.30

Release notes for llm-anthropic 0.30, the Anthropic plugin for Simon Willison's `llm` command-line tool. The update adds support for Claude Sonnet 5.5, a new `llm anthropic refresh` command that pulls the current model list directly from Anthropic's API (so new models work without waiting for a plugin release), and an `llm anthropic count` command that uses Anthropic's free token-counting API to preview prompt token usage before sending a request.

Python
Simon WillisonAnthropicClaude Sonnet 5.5

ai-infra· Added 8 Oct 2026, published 28 Sep 2026

simonwillison.netarticle🧠 AI

Claude Sonnet 5.5

Simon Willison's first-look at Claude Sonnet 5.5, Anthropic's new Sonnet release priced the same as Sonnet 5 but described as 30%+ faster and up to 30% cheaper while beating it on benchmarks. He runs his standard 'pelican riding a bicycle' SVG/WebGL test across thinking-effort levels, notes Sonnet 5.5 hit the same runaway-thinking-token bug as Opus 5.5, and highlights that Sonnet 5.5 now powers the free tier of claude.ai, which he judges notably more capable than ChatGPT's free tier (running Luna 5.6).

Claude
AnthropicClaude Opus 5.5OpenAI+2

models· Added 29 Sep 2026, published 28 Sep 2026

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