Koi vs Vellum Ambient: on-screen help, side by side

Pick Vellum Ambient if you want to hand off tasks and keep working while they run, with your own choice of AI model. Pick Koi if you want help with what's on your screen right now, with dictation that runs on your Mac, calls recorded without a bot, and hard limits on what it will do for you. Both work over any Mac app, listen when you call them and draw on the screen to show you where to click.

Where Koi falls short of Ambient:

• No background tasks. Koi works while you watch, borrowing your pointer for each press.
• No choice of model, no bring-your-own key and no local models.
• No wider platform. Vellum's plans come with a computer of their own in the cloud, and on the bigger ones an email address and subdomain for the assistant.
• No free start. Ambient runs on Vellum's free Base plan with prepaid credits; Koi has a 3-day trial that needs a card.

We make Koi, so read this with that in mind. Ambient launched on September 24, 2026, and the launch write-up we draw on found no independent hands-on review yet. Facts about it come from Vellum's Ambient page, its pricing page and that write-up, checked October 16, 2026.

This is where they're closest. In Ambient's guidance mode, per the launch write-up, it draws an arrow or a ring with a caption of up to 80 characters to show where to click, attaching the arrow to a named control when it can, and leaves the click to you. Vellum's page shows it guiding people through apps like CapCut and QuickBooks, and you can circle something on screen yourself while you talk to show it what you mean.

Koi circles the exact button, highlights the exact sentence, or draws on a board over the screen: a diagram, a graph, a sum worked step by step. The marks look hand-drawn and go once they've served their purpose. Ask it to, and Koi clicks the button itself, then checks that it worked.

This is the real split. Double-press Fn and Ambient takes a task, like research or booking a flight, off your hands; it checks in when it's done or needs your approval. At the default risk setting, the write-up says, low-risk actions run on their own and the rest ask first.

Koi doesn't work in the background. It does the task on your screen, with subtitles saying what it's doing, and your pointer is borrowed for each press. And some steps it never takes, at any setting: it won't buy, pay, order, send, post, publish, delete, confirm, accept terms, sign in, or type a password or card number. It gets you to the button, circles it, and lets you press it. So Koi would find the flight with you, but the booking is yours. More in our guide to an AI that controls your Mac.

Both dictate into any text field. In Ambient you hold Fn to dictate, or select text and hold Fn to rewrite it by voice. The write-up, citing TestingCatalog, says its speech is turned into text by Deepgram and spoken back by ElevenLabs, so dictation goes through the cloud.

Koi's dictation runs on your Mac. Tap Fn + ⌥, talk, and Whisper writes it where your cursor is, offline, in 57 languages it tells apart by itself, unlimited on every plan, with a list of your own words. Rewriting is separate: select text, tap Fn + ⌘ and say “make it shorter”.

Ambient sends the screen you share to a cloud model, which Vellum says runs under a zero-retention policy by default. You can switch to other providers with your own keys, or point it at a local model through Ollama. Koi doesn't offer that: it uses its own models, online, and you can't bring a key.

During a call with Koi, your voice goes to the AI provider with no id for your account, and a picture of the screen goes with each question unless you switch that to only when you ask, or never. Koi's server keeps what the call cost, not what was said or shown. Documents, call transcripts and what Koi remembers about you stay on your Mac. See our trust page.

Vellum Ambient wins on:

• Tasks that keep running while you do something else.
• Model choice: your own keys, or a local model.
• A free way in, on prepaid credits.
• The platform around it: a cloud computer, and on bigger plans an email address and subdomain for the assistant. Vellum also says its assistant is open source and can run on your own hardware.

Koi wins on:

• Older Macs: macOS 14 and later, where Ambient needs macOS 15.
• Dictation that never leaves the Mac and works offline.
• Recording calls: tap Fn + ⌃, pick Online call or In person, and You and Them are written down on your Mac with the screen's video.
• Documents, flashcards, Study mode and a calendar, all kept on your Mac.
• Fixed limits on what it does with your Mac, checked by the app.
• A flat price instead of credits: Pro $20 a month, or Lifetime, $59 for the first 25 buyers, rising to $199.

• You want to delegate and come back later? Vellum Ambient.
• You want your own model, or a local one? Vellum Ambient.
• You want help with the thing on your screen, right now, that stops before anything risky? Koi.
• You want dictation, call notes and documents in the same app, kept on your Mac? Koi.

Koi's plans are on the pricing page. For another close match, see Koi vs VoiceOS, our HeyClicky review, or the best AI assistants for Mac.