Lance Martin

MTS @anthropicai

[Thariq @trq212]

https://t.co/R6exTuF7P8

[Lance Martin @RLanceMartin]

@mitsuhiko @trq212 yup, i just added a post on this :)

@badlogicgames / @mitsuhiko let me know if you want more details or if anything is unclear:

https://t.co/ugzhAkwtf2

[ClaudeDevs @ClaudeDevs]

With Opus 4.8, you can add system instructions mid-conversation without breaking the prompt cache.

More cache hits means lower cost and latency for your API requests.

[Lance Martin @RLanceMartin]

3/ some Opus 4.8 tips from testing:

> for long horizon work: pair 4.8 w/ Outcomes in Claude Managed Agents or /goal in Claude Code

> high effort is recommended default

> provide explicit triggering guidance for custom tools + sub-agents

see:
https://t.co/QnPf7B2OTK

[Lance Martin @RLanceMartin]

a number of useful tips + tricks for Opus 4.8:

1/ you can now update the system prompt mid-conversation w/o breaking the prompt cache.

previously, you had to add <system-reminder> tags to user messages (see @trq212's post).

https://t.co/wX5lYjBXvJ

https://t.co/hyd4vmxWXv

[Thariq @trq212]

https://t.co/taVRqwm4dG

[Lance Martin @RLanceMartin]

2/ to help with code migration to Opus 4.8, use our claude-api skill built-into Claude Code.

the skill bakes in the prompting guide + best practices for using Opus 4.8.

https://t.co/2Nv80iJDyo

[ClaudeDevs @ClaudeDevs]

We’ve updated Claude Code's built-in claude-api skill migration guidance for 4.8.

Run "/claude-api migrate" to update your model strings and suggest prompt improvements that are tuned for Opus 4.8.

[Dan Shipper 📧 @danshipper]

BREAKING:

Anthropic just dropped Opus 4.8—and it is a MONSTER

We've been testing for about a week @every and our verdict is they could've just called it Opus 5, it's that good.

Here's our vibe check:

- Beats GPT-5.5 on Senior Engineer bench. On our toughest benchmark Opus 4.8 scores a 63—a hair higher than GPT-5.5's score of 62, and a full 30 points higher than Opus 4.7. It tackled a ground-up rewrite of a production codebase, and actually built something that works.

HOWEVER: Coding performance varied a lot at different reasoning levels. We recommend using it on xhigh for best results.

- Incredibly good writer. Opus 4.8 scored a 79.6 on our writing benchmark—measuring models on real-world writing tasks we do all of the time like essay writing, promo email writing, and more. It beats GPT-5.5 by 6 points. It produces well-written prose with fewer "AI-isms". It's also very good at writing in your voice given the right context.

HOWEVER: Writing performance also varied with reasoning levels. Medium reasoning had higher incidence of AI-isms—we found best results with high.

- Beast at knowledge work. Opus 4.8 is very good at general knowledge work tasks like report creation, research and more. It produced the best PowerPoint one-shot we've ever seen on our deck generation benchmark.

- Emotionally intelligent, willing to question the frame. I've also found it to be quite good at talking through psychological or interpersonal issues. It has a high EQ, and it's also good at not glazing and helping to expand your perspective. Its thought process feels extremely rich and dynamic.

THE BAD:
These days a model is only as good as its harness, and Codex is still a far superior harness to the Claude Desktop app. This has kept me using Codex + GPT-5.5 as my daily driver, but I am flipping back and forth a lot more between Codex and Claude.

Anthropic is back baby!

Read the rest on @every:
https://t.co/vuORiDXkxX

[ClaudeDevs @ClaudeDevs]

We’ve updated Claude Code's built-in claude-api skill migration guidance for 4.8.

Run "/claude-api migrate" to update your model strings and suggest prompt improvements that are tuned for Opus 4.8.

[Sholto Douglas @_sholtodouglas]

Huge credit to the OAI team for solving the unit distance problem with 5.5 - it is now my go to example that models can in fact pull together disparate ideas into new discoveries.

As with all 4 minute miles, we had to try and cross it too! Turns out mythos solves it with a cute, simple proof. This implies some serious overhang in discoveries!

[Chris Olah @ch402]

https://t.co/udIVxLdid5

[Jake Eaton @jkeatn]

"For the last few months, Anthropic has used Mythos Preview to scan more than 1,000 open-source projects, which collectively underpin much of the internet—and much of our own infrastructure.

So far, Mythos Preview has found what it estimates are 6,202 high- or critical-severity vulnerabilities in these projects (out of 23,019 in total, including those it estimates as medium- or low-severity)."
https://t.co/9XzxxDFOnB

[David Soria Parra @dsp_]

The release candidate for MCP 2026-07-28 is out. The protocol is now stateless: no handshake, no session id, any request can hit any server instance. Plus extensions as first-class (MCP Apps, Tasks), auth hardening, and a proper deprecation policy so we don't have to do this again.
https://t.co/XRLTu1BSkB

[Lance Martin @RLanceMartin]

we've updated the claude-api skill to help onboard on self-hosted sandboxes.

you can invoke this in the latest version of Claude Code (with the "/claude-api" command) and ask questions.

see repo here:
https://t.co/wKlvKQDwJu

more cookbooks here:
https://t.co/WOYFBmkwHB

[Lance Martin @RLanceMartin]

we just added self-hosted sandboxes to Claude Managed Agents.

i've been excited about this for a while: you can now connect many more "hands" (customizable execution environments) to the agent.

here's a few interesting articles covering what you can do ...

[Lance Martin @RLanceMartin]

@vercel: use a Vercel Sandbox for fine control over both networking and credentials. Vercel runs compute inside / adjacent to your own network. lets you reach internal databases, private APIs, or services.

https://t.co/0vxiLJbYsv

[Lance Martin @RLanceMartin]

@karpathy @martinamps welcome Andrej! very excited to have you here.

[Andrej Karpathy @karpathy]

Personal update: I've joined Anthropic. I think the next few years at the frontier of LLMs will be especially formative. I am very excited to join the team here and get back to R&amp;D. I remain deeply passionate about education and plan to resume my work on it in time.

[Lance Martin @RLanceMartin]

this pairs well with the claude-api skill (bundled with Claude Code).

ask Claude Code to investigate the cache misses using the diagnostics to guide.

console link:
https://t.co/02EOpLFNgm

docs:
https://t.co/eUmyBLWXkB

https://t.co/AnImwG6ojk

[ClaudeDevs @ClaudeDevs]

Claude Code ships with a built-in skill for working with the Claude Platform.

Useful for model migrations, using API features (e.g., prompt caching), or onboarding to newer APIs like Claude Managed Agents.

[Lance Martin @RLanceMartin]

Claude Console now gives diagnostics on prompt cache misses.

it will attribute cache misses to messages, system prompt, tool, or model changes.