Towards AI

we read 11 posts on anthropic's engineering blog to see how their engineers actually use claude code.

the one we didn't expect: their test scripts have a --fast flag that runs a random 1% or 10% of the tests. claude can't tell time, so left alone it will spend hours re-running everything.

they also keep test output to a few lines and put ERROR plus the reason on one line, so claude can grep for it instead of reading thousands of log lines.

the other 6 habits are in the reply 👇

@AnthropicAI just dropped 3 fable reset!

thanks dario

x.com/claudeai/statu…

Code Mode, clearly explained!

most MCP servers give your AI one tool per endpoint. every tool's name, description and inputs sit in context before it does anything

that breaks on big APIs. cloudflare's API has 2,594 endpoints. as tools that's about 1.17M tokens of definitions, and still ~244K if you only list required inputs

so their MCP server has two tools

search() lets the AI write code to search the API spec and get back only the endpoints that match. the spec itself never enters context

execute() runs the AI's code against those endpoints in a locked-down sandbox. no file system, no env vars, outside fetches off by default

two tools, ~1,000 tokens, and it stays that size however big the API gets

where it really pays off is multi-step work. say you need every customer refunded twice this month (made-up example, we didn't run it). one tool per endpoint means every page of payments flows through the model. with code mode it writes one script that pages through, filters, and returns five names

to be clear, those numbers only count tool definitions. search results and outputs still cost tokens, so it's not a guaranteed speedup. and it runs over MCP, it doesn't replace it

the catch is your AI now runs code it wrote. you still need scoped tokens, error handling and a human check before deletes, payments or emails. a sandbox protects your machine, it doesn't stop a refund call the token is allowed to make

anthropic ships the same idea in the claude SDK as programmatic tool calling

blog.cloudflare.com/code-mode-mcp/

Big win for debugging with coding agents!

OpenCode just shipped Browse. It lets any agent (OpenCode, Claude Code, Codex, Cursor) drive your real browser with your tabs, logins and extensions.

Agents using your logged in browser isn't new. Playwright MCP has an extension for it and Claude in Chrome does it too. What's most surprising is how much care went into everything around it.

The agent can type your saved passwords without the value ever showing up in its transcript.

It can save the network traffic as a HAR file with secrets removed. A flight recorder keeps the last minute of video, so when something breaks you get the moment it broke.

For debugging this is a big deal. A lot of bugs only happen when you're logged in as a real user with real data, and your agent's fresh test browser never sees them. Now it can reproduce the bug, grab the failing request and fix the code.

x.com/opencode/statu…

your AI remembers too much, and anthropic just showed why that makes it worse

they gave claude a memory folder and let it play pokémon red

sonnet 3.7 saved everything. a file for every battle, every item, every person it met. 413 files in 225 folders after about 10,000 steps, and one badge

fable 5 saved 10 files and won four badges. opus 5.5 kept a small folder too and beat the game

the big folder kept going stale because the game changes every turn. at one point sonnet 3.7 spent 17 steps making 6 files and deleting 9 without playing at all

the better models only saved what they couldn't see again. money and location are on screen every turn, so they skipped them. plans, tested rules and traps only exist if claude writes them down. after 7 failed catches fable 5 wrote "If 3+ balls fail in a row, VARY the timing"

what's most surprising is that strict rules made it worse. telling opus 5 and opus 4.7 to "record only failures" took away much of what memory gave them. anthropic now just tells claude what memory is for and lets it decide

wrong notes are the other risk. claude wrote down that a building was on the wrong side of a cave, trusted it, and kept falling back to the route it came from. a "dreaming" pass that checked the note against the session log fixed it

so before adding another line to your CLAUDE.md, ask if claude could just look it up

x.com/AnthropicAI/st…