Amp 2026.09.01

Amp 2026.09.01 was released on September 1, 2026.

Summary

Fable 5.1 Claude Fable 5.1 now powers Amp's ultra mode, replacing Fable 5. It's very good at writing, very good at taking direction mid-task, and very good at working on its own. And it costs less...

Release Notes

Fable 5.1 Claude Fable 5.1 now powers Amp's ultra mode, replacing Fable 5. It's very good at writing, very good at taking direction mid-task, and very good at working on its own. And it costs less to run. Long Tasks and Proof of Work What won us over is how much better it got at long horizon work, at giving proof of its work, and at iterating on that proof. It runs for hours on its own, and when the proof doesn't hold up, it goes back and fixes the work, then proves it again. Some examples: - Hamish told it key presses felt laggy in our iOS app and asked it to find out why. Two hours later it had a side-by-side video of the old and new builds typing the same sentence on an iPhone simulator. Along the way it caught a two-pixel height difference in its own comparison, corrected it, and re-recorded. Typing latency in Safari went from 85 ms to 8 ms. - Thorsten recorded his screen creating a new thread on ampcode.com and asked it to make that twice as fast, however long that may take. Fable 5.1 pulled every frame out of the recording to time each step, then found the biggest delay was waiting for the server to finish creating the thread. Creating a thread got 45% faster. Writing Writing is where it impressed us the most. So far we haven't been big fans of using AI for prose. Fable 5.1 changed that. The text it produces reads more like it was written by a person. It explains the idea behind a change instead of every technical detail, and draws a diagram when that's clearer than a paragraph. We ended up using it for our new docs pages, where it not only surprised us by writing concise prose but also by running the features on a dev server, executing them end to end, and documenting them with screenshots and demo videos. Steering We steer it a lot more now. Fable 5 would sometimes ignore an instruction sent mid-task and carry on with the work it already had. Fable 5.1 does both: it finishes the original task, does what you just asked, and reports on each separately. It addresses every instruction you give it, even several at once. It works great now that Enter steers by default. Cheaper And it costs less: ultra threads are about 35% cheaper than before. Cache reads are 75% cheaper than on Fable 5, and in a typical Amp thread, over 90% of tokens are cache reads. How To Use It ultra is for the work where the outcome is clear and the path is not. Fable 5.1 is at its best there. A few habits help: - Tell it what done looks like, and how to prove it. Example: "The sidebar stutters when scrolling through a few hundred threads. Find out why and fix it. Show me a video of scrolling before and after on the same thread list, and frame times measured in Safari, not Chrome." - Steer it while it works. If it's heading somewhere you don't want, say so in the moment. You can also hand it new tasks while it's busy; it addresses all of them without dropping the one it's on. What the Team Says Very impressed by Fable 5.1. It's very good at writing, it's very good at... everything really? I'm in a thread where I constantly reply to 2-3 different things and it perfectly keeps them apart. It's like having two conversations at once. — Thorsten Ball I've also been impressed with Fable 5.1. Feels less hand-wringy than Fable did. — Camden Cheek In my code reviews I agree with its changes more than I agree with the previous Fable's. And I steer it a lot more, because it handles multiple requests at once. — Hitesh Sagtani

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Other Recent Amp Releases

• 2026.10.19 (October 19, 2026)
• 2026.10.16 (October 16, 2026)
• 2026.10.13 (October 13, 2026)
• 2026.10.12 (October 12, 2026)
• 2026.10.12.2 (October 12, 2026)

Upgrading from 2026.09.01? See all 19 releases since.

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