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Claude Ultra drops its 5-hour cap; a malicious Claude Code extension circulates through Cursor's marketplace
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Anthropic removed the 5-hour limit on its top plan, and Cursor reported a tampered Claude Code extension in its marketplace. Also: a dispute over whether to compact long agent sessions or let agents retrieve from the full transcript, DHH on reading less agent-written code, and Theo on why the choice of harness matters less.

Claude Ultra: long sessions no longer stop at the 5-hour limit

Anthropic renamed its plans. Max 5x is now "Max" ($100/month) and Max 20x is now "Ultra" ($200/month). Verified Ultra accounts lose the 5-hour limit, starting with most existing subscribers. Newer accounts keep a temporary limit until they are verified, and you get an email when it is lifted. Weekly limits stay the same . Claude's product lead for subscriptions says the Ultra weekly limit stays at 10x Pro. The change is meant to let you "keep building without getting blocked mid-session," and it rolls out in stages . This matters most for long unattended or parallel agent runs. Before, those runs could hit the 5-hour limit partway through. Now only the weekly limit applies.

Check your Claude Code extension if you use Cursor

Cursor found a modified, malicious Claude Code VS Code extension in its IDE extension marketplace, affecting at most 5,000 users. Cursor took the marketplace down, worked with providers to neutralize the malware, then reinstated the marketplace. It asks all customers to update to Claude Code for VS Code 2.1.314. A blog post explains how to find the malicious package . Alex Albert says the extension was a tampered copy that Anthropic did not build or publish .

Compaction vs. retrieving from the transcript

The author of Mainplane (MIT-licensed) measured compaction on a real ~400k-token Opus 5.5 session. It took 38 s and cost $1.99 with an expired prompt cache, and 29 s and $0.17 with a cache hit. The summary also tends to drop exact error messages, file paths and numbers . Mainplane takes a different approach. It saves every session as a file, and when the context fills, it starts a new session with one instruction: "You are continuing session X. Retrieve key context from it as you go." The agent then copies exact lines from the old session as it needs them. The author reports 15 s and $0.10 to resume, with no dependence on the cache .

Jediah Katz disagrees: "Done properly, compaction should be cheap and near instant." The model summarizes itself, so the prompt cache still hits. You start compaction a little early and asynchronously, so the summary is ready when the window fills. His suggestion is to pair compaction with access to the past transcript, not to replace compaction with it. He points to his dynamic context discovery write-up .

DHH: agents improving existing apps, and less human code review

In his Kaigi on Rails keynote, DHH says he had an agent apply speed-ups learned from other Campfire implementations to the Rails version. It got about 20× faster in a few hours . Agents also found and fixed security holes in code humans had written . On his Rails agent benchmark, the best agent, Claude Opus 5.5, completes 65% of tasks . He built a PDF-signing app from one prompt ("work roughly like... Apple's preview app"), made one follow-up change, and shipped it .

His position on review: line-by-line reading can't keep up with agent output. He still reads code that touches billing or data integrity . He expects shared libraries to stay, with fewer abstractions and more inlined or repeated code ("Do repeat yourself"). Agents in his evals don't know the whole framework and end up recreating features Rails already has .

Is the harness still worth choosing? Theo vs. Steinberger

In "Are Harnesses Dead?", Theo argues that picking a harness barely matters now. Choose for the capability and price you need. He estimates that running Codex models in Claude Code versus in Codex differs by "three to 5% maybe" . One practical detail: T3 Code's model picker actually picks the harness. Skills and plugins you set up for Claude Code don't carry over when you switch to Codex, so set them up in each harness . The T3 Code MCP adds tools without replacing a harness's built-in ones. With it, an agent can search T3 Code history, message other threads, or start subagents in another harness . He also says he set Claude to work after noticing unexpected failures. It set up alerting, monitoring and tracing to pinpoint when, where and in which regions failures occurred, and wrote a report he sent to Cloudflare .

Peter Steinberger argues the other side. He says to use your own harness, not one "where companies change what you can or can't do at will" . He points to a report that around Oct 27, Claude Code picked up a server-side rule with no setting to turn it off. The rule permits original games, genre games, and games built from your own designs and assets, but not recreations of a specific existing game .

Worth studying

  • nesformer (repo): Drew Breunig used Opus 5.5 to build a NES 6502 CPU emulator into the weights of Qwen3.5-4B, with ROMs running very slowly . It took two prompts. The first was a feasibility study: read the qwenputer article and code, then estimate model size and clock speed. The second: "I think we should build it! Just for fun. It's okay if it's not fast". It asked for weights plus a CLI that runs a ROM . Opus found and used a set of NES CPU conformance tests released 15 years ago .
  • Rust rewrite with no Rust developers: Katelyn Lesse said on Latent Space that Anthropic rewrote its Messages API in Rust. Claude wrote the code, humans wrote the plan and checked that old and new matched on real traffic, and CPU use dropped 40–50% .
  • Test MCP connections before relying on them: OpenAI's finance team found error rates of 40% or more on some big-name MCPs, so it brought the data in-house . It says Codex got it "about 80% of the way" to a product, and it built the rest on ChatGPT's plugin primitives .

Short notes

  • Theo switched Opus 5.5 from extra high to high effort and says it is "better almost all of the time" .
  • Antigravity's agent features are now available in Android Studio .
Claude Ultra drops its 5-hour cap; a malicious Claude Code extension circulates through Cursor's marketplace
David Heinemeier Hansson (DHH)
Profile
  • DHH’s strongest demonstrated use was improving existing software: he had an agent apply optimizations learned from other implementations to Campfire, making its Rails version about 20× faster in a few hours; he also reports agents finding and fixing security holes in his human-written applications.
  • For a small PDF-signing app, he prompted for behavior modeled on Apple Preview, made one follow-up request to place the signature above the cursor, then shipped the result.
  • In DHH’s Rails-agent benchmark, Claude Opus 5.5 completed 65% of the tasks; he described it as the best agent in that benchmark at the time.
  • He says line-by-line review can bottleneck agent-written code, but still considers human review important for critical areas such as billing and data integrity, where he does not yet have confidence to deploy without reading the code.
  • DHH expects agent-friendly codebases to retain shared libraries while using fewer abstractions and less indirection, with more repetition and inlined code; his rationale is that agents can work with repeated code and that changing architecture has become cheaper.
Keynote: Where the tracks go next / David Heinemeier Hansson - Kaigi on Rails 2026
Latent Space
  • For a domain-specific agent product, build on existing Codex/ChatGPT plugin primitives before assuming model changes are necessary: OpenAI’s finance team said 95% of its build was feasible without changing the model, and Codex provided about 80% of the product; the differentiating layer was domain-specific data, UI, or integrations.
  • Test integrations instead of trusting their advertised availability: the team found error rates above 40% in some major-name MCP connections and chose to bring data in-house to control the experience end to end.
  • Evaluate coding agents on more than passing checks: combine verifiable tests (compilation, syntax, expected outputs) with human judgment of maintainability, testability, and idiomatic design; pairwise human preference can help train for that subjective quality.
  • Validate eval grading before trusting scores: evals are imperfect proxies, and faulty answer keys or grading can invite reward hacking; the team found incorrect keys and poorly specified prompts in its financial evals.
Building ChatGPT for Finance — Joseph Kim, OpenAI's Head of Financial Services
Theo - t3․gg
  • In a reported backend incident workflow, he used Quad after noticing unexpected failures; it set up alerting, monitoring, and tracing to identify when and where failures occurred, including by region, then produced a report for Cloudflare.
  • T3 Code’s MCP can let an agent search T3 Code history, message other threads, and spawn subagents using another harness, while leaving the selected harness’s built-in tools available. Harness-specific skills and plugins do not automatically carry over when switching harnesses, so configure them for the other harness too.
  • With Eve, he and a collaborator built a Discord T3bot that could be told to take over and land a PR. Eve agents can be configured in project folders with an instruction file, a chosen model, skills, TypeScript tools, a sandbox, connected channels such as Discord or Slack, MCP connections, subagents, and schedules.
  • He recommends choosing for the capability and price needed rather than loyalty to a harness; his rough estimate for the difference between using Codex models in Claude Code versus Codex was 3–5%, possibly negligible.
Are Harnesses Dead?
Peter Steinberger
Profile
  • Steinberger said he spent his available time deeply tinkering with models; when coding problems block him, AI can solve them or give him pointers that let him resume, making his project speed incomparable with before.
  • He said a key factor in OpenClaw’s success was pairing capable models with a more capable harness, adding WhatsApp, and instructing the model to speak more like a friend; from his phone, he could ask the agent to do nearly anything he could do on his computer.
  • His current agent-design challenge is making agents proactively help and send messages people actually want to read—not generic messages or random emails—despite users having different goals and ways of thinking.
KI-Star Peter Steinberger: "KI könnte bald Krebs besiegen" | krone.tv Message Macht Medien
Harrison Chase
Profile
  • LangChain’s Deep Agents provides a modifiable agent harness with a filesystem, sandbox, or code interpreter; skills and memory; long-context summarization and tool-output offloading; prompt caching; human-in-the-loop controls; planning; and subagents. The components can also be built more granularly with LangGraph and LangChain.
  • LangChain uses Open SWE internally as a coding agent for writing and reviewing code and triaging incidents; QA is a planned use. Open SWE is open source.
  • A practical improvement loop is to build an agent version, test it quickly, deploy to a small user group, monitor it, and feed findings into the next build. LangSmith Engine automates parts of that cycle by monitoring traces, clustering and diagnosing issues, proposing fixes via PR, and creating tests and evals; its v2 can test fixes in preview deployments and run red-team probes.
Why Own Your Intelligence? Harrison Chase Keynote | Interrupt London
Jason Zhou
  • /REA-growth is an open-source workflow for generating a company growth blueprint with a timeline of SEO, AEO, ads, and social activity; Jason Zhou links the Treg repository for updates.
  • In the Lovable example, Claude Code pulls data, does the analysis, and writes the report, while Treg provides a pay-per-call data catalog that identifies each provider. The analysis combined sitemap and backlink data, traffic estimates, ads, buyer-question answers, and company posts, then matched 343 dated company moves against monthly traffic. The launch post quotes $0.58 for the teardown, while the article reports $0.62 in total data costs.
Introducing /REA-growth skill Reverse-engineer any company's growth - Name any company, get its growth blueprint - Every move on its time… [@treg_ai](https://x.com/treg_ai) repo (🌟for updates): [https://github.com/superdesigndev/treg](https://github.com/superdesigndev/treg) Reverse Engineer Any Company's Growth in 10min
swyx

Anthropic reportedly rewrote its Messages API in Rust despite having no Rust developers: Claude wrote the code, while humans wrote the plan and checked that the old and new implementations matched on real traffic; the rewrite reportedly reduced CPU use by 40–50%.

Anthropic rewrote its Messages API in Rust. Zero Rust devs on the team. Claude wrote the code. Humans wrote the plan and checked old vs n…
Simon Willison's Weblog

Drew Breunig used Opus 5.5 to build nesformer, baking a working NES 6502 emulator into Qwen3.5-4B weights; NES ROMs such as Super Mario Bros. run very slowly inside the model. His workflow started with a feasibility prompt asking the agent to study the qwenputer article and relevant code, then explore NES CPU-and-RAM emulation, required model size, and whether smaller models could reach standard clock speed. He followed with a build prompt that explicitly prioritized a fun working result over speed, requiring model weights and a CLI that could run a ROM. Opus found and used an existing NES CPU conformance-test collection, illustrating how an agent can locate older test suites to validate an unusual project.

dbreunig/nesformer
Jediah Katz

Jediah Katz argues compaction can be cheap and nearly instant if the model summarizes its own session while preserving a prompt-cache hit, and compaction starts asynchronously early enough for the summary to be ready before the context fills. He recommends transcript access as a complement to compaction, not a replacement, and points to his dynamic-context-discovery write-up.

The quoted Mainplane author argues that compaction summaries can lose exact errors, paths, or numbers, and reports that a roughly 400k-token Opus 5.5 session took 38 seconds and $1.99 to compact after cache expiry, versus 29 seconds and $0.17 with the cache. Mainplane’s alternative keeps the full session record for retrieval in a new session; its author reports 15 seconds and $0.10 to resume, claiming this avoids cache dependence and paraphrase.

This is not right. Done properly, compaction should be cheap and near instant. Here's how: You get a cache hit by having the model summar… Compaction is a mistake. When an agent's context fills up, tools like Codex and Claude Code compact it: 1. The model prefills the entire …
swyx

Thariq warns that coding agents can create a productivity illusion: you may feel busy and work constantly while little is actually happening, possibly as avoidance of other parts of life.

There’s 100% a kind of mania you can get into with coding agents, where it feels like you’re getting a lot done and working all the time …
Kent C. Dodds 🐨

Kody is developing “profiles” that let users or their agents create token/MCP connections with only a subset of the account’s permissions, intended to make access safer and more auditable. Dodds said the feature would probably be finished and released that day; this was an expected release, not confirmation that it shipped.

Working on a new feature in Kody called "profiles" which allows you/your agent to create a token/mcp connection that has a subset of perm… Man, the AI-reply bots are extremely excited about this feature. But really it's a great feature! It'll probably be done and released tod…
Alex Albert

Claude renamed Max 20x to Ultra ($200/month) and removed its 5-hour limit for verified Ultra subscribers, allowing longer build sessions without that mid-session block; weekly limits remain unchanged. Newer accounts keep a temporary limit until verified, and removal is rolling out in stages.

We’re renaming our Max plans: Max 5x → Max Max 20x → Ultra Max is still $100/month, and Ultra is still $200. If you’re a subscriber, ther… I lead product for Claude subscriptions. Today we're renaming our Max plans, and I want to explain why. When we launched our top plan in …
Peter Steinberger 🦞

Peter Steinberger called OpenRouter’s provider-routing rebuild smart, but said unpredictable inference quality had usually led him to recommend skipping the middleman—a practitioner caveat for developers evaluating routed model access.

This is smart. Wild that this wasn’t the default. Unpredictable inference quality was usually why I recommended skipping the middleman. [… Read more about our approach: [https://openrouter.ai/blog/announcements/how-we-rebuilt-provider-routing/](https://openrouter.ai/blog/anno…
Jason Zhou

A Futer builder used the /rea-growth skill to analyze Playtomic for $0.39, finding that 88 of its top 100 Google keywords in Spain were club names, that Playtomic had no active Meta ads or paid search, and that its 35× traffic jump in 2025 came from moving domains; the builder planned to adapt Playtomic’s club-page idea for Futer. Jason Zhou highlighted the findings as insights generated by the /REA-growth skill.

i'm building futer, an app for people who organize amateur football games. so i ran /rea-growth on playtomic, the biggest court booking a… Some crazy alpha insights generated from /REA-growth skill! [https://x.com/ferlogs/status/2116237734926746084](https://x.com/ferlogs/stat…
LangChain
  • Deep Agents is a modifiable base harness with practical building blocks: a filesystem, sandbox, or code-interpreter execution environment; skills and memory; long-conversation summarization; large-tool-call context offloading; prompt caching; human-in-the-loop controls; planning; and subagents.
  • LangChain describes Open SWE as its internally used, open-source coding agent for writing and reviewing code and triaging incidents, with QA planned. For agents that need a sandbox, its recommended pattern is to run the agent outside the sandbox and connect to the sandbox as a tool; Managed Deep Agents packages deployment through mda deploy.
  • A useful iteration loop is to build, test quickly, deploy to a small user group, monitor, and feed the learnings into the next version. LangSmith Engine can automate parts of that loop by monitoring traces, clustering and diagnosing issues, proposing fixes via PR, and creating tests and evals; with LangSmith Deployments it can test a fix in a preview deployment. It can also red-team agents with new probes and accept agent self-reports of problems attached to traces for later analysis.
Why Own Your Intelligence? Harrison Chase Keynote | Interrupt London
Boris Cherny

Claude renamed Max 20x to Ultra ($200/month) and is removing the five-hour usage limit for verified Ultra accounts. The change starts with most existing subscribers; newer accounts keep a temporary limit until verification, and weekly limits are unchanged.

We’re renaming our Max plans: Max 5x → Max Max 20x → Ultra Max is still $100/month, and Ultra is still $200. If you’re a subscriber, ther…
Peter Steinberger 🦞

Peter Steinberger recommends using your own harness rather than one controlled by a company that can change what it permits . His example is a report that Claude Code received a server-side, non-disableable restriction against recreating specific existing games, while still allowing original games, genre games, and users’ own designs and assets .

Another reason why you wanna use your own harness and not one where companies change what you can or can’t do at will. [https://x.com/cha… ANTHROPIC IS CRACKING DOWN ON VIDEO GAME REWRITES 🚨 Claude Code picked up a new rule around Oct 27, sent from Anthropic’s servers under a…
Kent C. Dodds 🐨

Kent C. Dodds is working on a Kody feature called “profiles” that lets users or agents create token/MCP connections with a subset of the account’s permissions, intended to make access safer and more auditable; the post describes it as in development, not released.

Working on a new feature in Kody called "profiles" which allows you/your agent to create a token/mcp connection that has a subset of perm…
Alex Albert

The Claude Code extension at issue was a tampered copy, not an extension built or published by Anthropic—a provenance caveat for developers evaluating Claude Code extensions.

[@amasad](https://x.com/amasad) This was not an official Claude Code extension. It was a tampered copy of the Claude Code extension, whic…
LangChain

LangChain promoted DeepLearning.AI’s Loop Engineering with LangChain Deep Agents course, which teaches long-running agent workflows using loops to check outputs, event-triggered runs, and harness improvements based on traces across runs; the course is taught by Syd Runkle and Evan Garza .

Build reliable agents for long-running tasks. Loop Engineering with [@LangChain](https://x.com/LangChain) Deep Agents: add loops that che…