Mark. @markmdev
Member of Technical Staff @a____t____g 9x hackathon winner SF San Francisco Bay Area Joined April 2025-
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I resigned from Anthropic today. I spent the last three years doing pretraining research at both OpenAI and Anthropic. Neither company is acting responsibly. They are racing straight to self-improving superintelligence and gambling with our lives. More thoughts below.
This is GPT-6 Astra. Anything you can do on a computer, Astra can do for you. Fast.
i'll never forget that time someone demo’ed me a language model at a hackathon in 2022 and I thought to myself "this is just GPT-3 but worse" and it turned out to be Claude 1
WE RESEARCHED ALL 6,077 YC STARTUPS We wanted to know: do these startups share anything in common? And how have trends shifted over time? Here's what we found:
You got claudex. But do you have fabledex? fabledex.markmdev.chatgpt.site
WHERE ARE YC FOUNDERS NOW? @_javokhir and I were curious where they go "after the startup". So we ran Deep Research on ALL 11,398 founders who have ever gone through YC. Here's what we learned: joinedanthropic dot com
Personal update: I'm taking a leave of absence from YC to join Anthropic. I'll be working with @NotTomBrown on the compute team. Powerful AI has the potential to improve the life of every human on earth and, as we enter the early stages of recursive self-improvement,
If Codex repeatedly reconnects after you send a message or takes 15+ seconds before it starts responding, check whether the task has accumulated lots of screenshots. In my case, completed compactions retained raw base64 image payloads, causing later turns to repeatedly process a huge image-heavy history. Removing those retained image nodes restored 4-8s response times. I packaged the repair for this specific symptom as a skill: github.com/markmdev/codex… (Just send it to your Codex if you hit the same error)
Why is nobody talking about this Codex feature? You can select anything in the agent's response, click "More details", and it creates a new ChatGPT chat that already has all the context and just explains the thing to you. It helps so much when you don't understand something in Codex's answer. Before, I'd open a side chat, write a prompt, and wait while it double-checks everything it already knows. Now it's one click, and the explanation is almost instant. And it's not just about code either. If you're learning something new, just use it all the time. It's extremely powerful.
I embedded all ~6,000 launched Y Combinator companies by what they actually do, and mapped idea-space.
Attending AI Engineer World's Fair this week. My Day 1 saved sessions lean coding agents / AI-native SDLC: Codex, Uber uReview, 1M AI-generated PRs, production code access, Claude long-horizon, Shopify River, Figma, Cursor. If you're there too, what are you prioritizing?
@JustinBleuel @ChatGPTapp fork_context:true subagents continue parent-thread work instead of following delegated prompt github.com/openai/codex/i…
1. Subagents should not stop when I stop the main thread 2. I can’t steer from iOS app 3. When the main thread is just waiting for a subagent and I want to steer the main thread - it reacts to it after a few minutes, instead of instantly. 4. Chrome use doesn’t work reliably. Agents have to fallback to Computer Use very often. 5. Same with in-app browser. 6. I’d love to see what skills were used and what files were read since the last turn. 7. I want to be able to attach more than 1 heartbeat to a thread 8. If I have too many skills, system prompt compacts their descriptions (I believe this threshold is about 2% of the context window). This makes sense, but I want it to be configurable at least. I have around 150 skills, and agents can’t see full descriptions… Otherwise, it’s incredible! I feel like I can do 90% of my computer tasks from my phone now 🤯
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