Cursor Composer: Building a fast frontier model with RL

I dropped cursor for the precise reason you mention: reliability.

Countless times my requests in the AI chat just hang there for 30+ seconds more until I can retry them.

When I decided to give Claude Code a try (I thought I didn't need it because I used Claude in Cursor) I couldn't believe how faster it was, and literally 100% reliable.

EDIT: given today's release, decided to give it a go. The Composer1 model _is_ fast, but right at the second new agent I started I got this:

> Connection failed. If the problem persists, please check your internet connection or VPN

I too have tried them all and have settled with Cursor being the best. That said I see the current space split between folks like me who know generally what I want built and appreciate a tool that helps me get to goal quicker and on the otherwise of the spectrum, folks who want the tool to orchestrate most of the engineering. I have no opinion on which is better but for me I sit on the first camp. In that camp Cursor is by far the best tool.

Yep, it just works seamlessly. Sure, it hangs sometimes, but their UI allows you to retry or undo changes to an earlier point in the conversation easily. The autocompletion is nice as well and pretty satisfying to tab through the small and menial things when refactoring.

> I’ve tried all the popular alternatives (Copilot, Claude Code, Codex, Gemini CLI, Cline)

Can't help but notice you haven't tried Zed!

You tried Claude and still prefer cursor?

I feel like that's like having a lead in producing better buggy whips.

I run Claude Code in the background near constantly for a variety of projects, with --dangerously-skip-permissions, and review progress periodically. Tabbing is only relevant when it's totally failing to make progress and I have to manually intervene, and that to me is a failure scenario that is happening less and less often.

We also are big Tab users here at Cursor. In the blog we talk about the motivation for this project came from thinking about a Tab-like agent.

It's great. BUT: Wish they had selected another shortcut like shift+tab.

Every time I write code myself I find myself racing the AI to get an indentation in before the AI is done... gets annoying

Tab model is fantastic but I wish it was somehow aware of the conversation happening in the currently active AI chat session.

There is a youtube livestreamer building with it now, if you are looking for direct feedback: https://www.youtube.com/watch?v=1bDPMVq69ac

Which model did you distill it from? Great work! PS getting a few scenarios where it doesn't follow rules as well as sonnet 4.5

Why did you stop training shy of the frontier models? From the log plot it seems like you would only need ~50% more compute to reach frontier capability

Is the new model trained from scratch? What training data went into it?

Is it true that Cheetah is Grok Code Fast 2? Does this mean that the new Cursor model is also based on Grok?

How do you work with multiple agents?

is Composer a fine tune of an existing open source base model?

There are lots of good models we like here. But we agree that getting the right point on the smart+fast graph can make agentic coding feel really good.

(Cursor researcher)

There is a footnote that should help with the models. Training is a harder thing to report on, but roughly our finding here is that RL scales.

There’s two different kinds of users, on one side people are more hands off and want the model to autonomously handle longer tasks on its own with minimal guidance, and on the other side is users who want to interactively collaborate with the model to produce desired results. Speed matters much more for the second case, where you know what you want and just want the model to implement whatever you had in mind as quick as possible. Intelligence/ability matters more for the first case when you don’t have full understanding of all the code. I think it’s context dependent for me where more serious work tends to be more interactive. The intelligence of a model doesn’t make up for issues due to lack of context to me.

> Sonnet 4.5 quality is about as low as I'm willing to go.

literally a 30 day old model and you've moved the "low" goalpost all the way there haha. funny how humans work

The reason I pulled out the comparison is to highlight how serious they are about all the important parts that make or break the AI coding experience - speed being very important to me. I’d rather catch my model doing the wrong thing quickly than having a higher chance of one-shotting it at the cost of having to do a lot of specification upfront.

Agree that Sonnet 4.5 is an excellent model. Would be curious to hear your experience using Composer though, it's quite good.

I tried going back to VS Code + Copilot a month ago. I only lasted 4 days because it was to bad. It was super slow and gave poor suggestions, but mostly it just flat out did not suggest anything. Cursor feels snappy in comparison and the suggestions are more often than not useful. The most annoying thing about Cursor tab complete, is that it is so fast that when I am doing something unusual then it will keep on jumping in with useless suggestions. They have a snooze function for this though.

Hey - really sorry to hear this - could you email me andrew@cursor.com? Here are 3 suggestions to try- 1. Reset your settings.json - if shared with vscode, sometimes settings can cause perf regressions 2. Could you try cmd-shift-p -> "capture and send debugging data"? Will send us some profiling data to debug 3. Clear your user data (will delete chats) as a last resort - cmd-shift-p, "reveal user data," close the app, then delete this folder and restart the app

you can use git worktrees and just have multiple Claude Code terminal instances working on each worktree. That way they don't clash, just delete the worktree when the task is done.

my very small nit is... why is the model called Composer?? of all things?? when there was already a Cursor Composer from 2024.

Cursor Cheetah wouldve been amazing. reusing the Composer name feels like the reverse OpenAI Codex move haha