5Simon Willison's Weblog·
Simon Willison releases sqlite-utils 4.0rc2, mostly written by Claude Fable for ~$149
Simon Willison published a release candidate for sqlite-utils 4.0, reporting that the majority of the code was written by Claude Fable (an Anthropic model) at a cost of approximately $149.25. The post is a practical case study in using a frontier LLM as a primary coding agent for a real open-source library release. It provides concrete cost and output data for agentic coding workflows.
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Anthropic Releases Claude Opus 4.5 with State-of-the-Art Coding, Agent, and Computer Use Capabilities
Anthropic has released Claude Opus 4.5, positioning it as the best model in the world for coding, agentic workflows, and computer use, with pricing reduced to $5/$25 per million input/output tokens. The model demonstrates significant token efficiency gains—up to 65% fewer tokens than prior models on equivalent tasks—alongside improvements in long-horizon autonomous task execution, multi-step reasoning, and self-improving agent behavior. The release is accompanied by updates to Claude Code, the Claude Developer Platform, and integrations with Excel, Chrome, and desktop environments. Early partner feedback from GitHub Copilot, Cursor, Notion, Warp, and others reports measurable benchmark improvements and new use cases previously out of reach.
Anthropic Releases Claude Sonnet 4.5: Top Coding and Computer-Use Model with Agent SDK
Anthropic has released Claude Sonnet 4.5, claiming it is the best coding model and strongest model for building complex agents, with a 61.4% score on OSWorld (up from 42.2% for Sonnet 4) and state-of-the-art performance on SWE-bench Verified. The release is accompanied by major product upgrades including checkpoints in Claude Code, a native VS Code extension, a Claude Agent SDK giving developers access to the same infrastructure powering Claude Code, and new context editing and memory tools in the Claude API. Pricing is unchanged from Sonnet 4 at $3/$15 per million input/output tokens. Early enterprise customers including Cursor, GitHub Copilot, Devin, Canva, and Figma report significant gains in coding, agentic, and long-context tasks.
Claude Opus 4.1 Released with 74.5% SWE-bench Verified Score
Anthropic has released Claude Opus 4.1, an incremental upgrade to Claude Opus 4 focused on agentic tasks, coding, and reasoning. The model achieves 74.5% on SWE-bench Verified (without extended thinking) and shows notable gains in multi-file code refactoring and large-codebase debugging. It is available to paid Claude users, Claude Code, and via API on Anthropic, Amazon Bedrock, and Google Cloud Vertex AI at the same price as Opus 4. Anthropic notes substantially larger model improvements are planned for the coming weeks.
Anthropic Introduces Claude Opus 4 and Sonnet 4 with Leading Coding Benchmarks and Agent Capabilities
Anthropic has released Claude Opus 4 and Claude Sonnet 4, positioning Opus 4 as the world's best coding model with 72.5% on SWE-bench and 43.2% on Terminal-bench, and Sonnet 4 at 72.7% on SWE-bench. Both models are hybrid (near-instant + extended thinking), support extended thinking with tool use in beta, parallel tool execution, and improved memory via local file access. Alongside the models, Anthropic is launching Claude Code as generally available with GitHub Actions, VS Code, and JetBrains integrations, plus four new API capabilities: code execution tool, MCP connector, Files API, and one-hour prompt caching. Pricing is unchanged from prior Opus and Sonnet tiers ($15/$75 and $3/$15 per million tokens respectively), with availability on Anthropic API, Amazon Bedrock, and Google Cloud Vertex AI.
The Batch: Claude Mythos 5 / Fable 5 debut, Apple AFM 3, Google Live Translate, OpenAI IPO filing, FrontierCode benchmark
Anthropic launched Claude Fable 5 (a safety-guardrailed model) and Claude Mythos 5 (same underlying model with safeguards removed, for vetted cyberdefense/infrastructure users via Project Glasswing with US government collaboration), both priced at $10/$50 per million tokens. Apple released five new Apple Foundation Models (AFM 3) spanning on-device and cloud tiers, built with Google and Nvidia infrastructure. Additional headlines cover Google's Gemini 3.5 Live Translate (70+ languages, real-time), OpenAI's confidential SEC IPO filing, a NotebookLM upgrade to Gemini 3.5, and Cognition's FrontierCode benchmark for code-quality evaluation where Claude Opus 4.8 leads at 34.3%.
sqlite AGENTS.md
Simon Willison publishes an AGENTS.md file for the SQLite project, a convention for providing AI coding agents with project-specific instructions and context. This follows the emerging practice of including agent-readable documentation files in codebases to guide LLM-based tools. The post reflects the growing ecosystem of conventions around agentic coding workflows.
datasette-agent 0.1a4
Simon Willison releases datasette-agent 0.1a4, an early alpha of an AI agent plugin for Datasette, the open-source data exploration tool. The release represents ongoing development of agentic tooling that allows LLMs to interact with SQLite databases through the Datasette interface. As an alpha release from a prominent AI tooling developer, it signals continued growth in the agent-tool ecosystem for data querying use cases.
RuBench: Repository-level agentic coding benchmark with native Russian task specifications
RuBench 1.0 is a new benchmark of 25 repository-level agentic coding tasks drawn from real fix commits in five live open-source projects, where task specifications are written natively in Russian in the style of customer requests rather than translated from English. The benchmark evaluates deployed product configurations including Claude Code with Opus 4.8, Sonnet 5, and Haiku 4.5, and Codex CLI with GPT-5.5, with the best configuration resolving 78.7% of tasks. A notable finding is that auditing trajectories of a fifth configuration (Claude Code + Fable 5) revealed that on 20% of tasks an official safeguard fallback silently re-routed the model to Opus 4.8, providing direct evidence that the deployed product rather than the underlying model is the actual unit of measurement in agentic evaluations.