Your first message creates the session, boots its machine in about a second, and hands the prompt to the agent.
A session starts the moment you send your first message from the home screen. Alpha creates the session, boots a machine for it alone, and hands your prompt to the agent, usually before you have finished reading your own message. To choose the agent, model, setup or repositories first, set them on the home screen. To go back to a session you already started, find it in the sidebar.
Starting a session takes four stages. Keep the tab open until your message has gone: attached files upload from your browser, and the message follows them. Once the agent has it, the turn runs on Alpha’s servers, so you can close the tab and the work carries on.
1
Send the first message
Press Enter in the home composer, or click the arrow button (Start the session). Everything you set on the home screen goes with the message: the agent, the model and effort, the permissions, plan mode, the setup, the repositories and any name you gave the session. Alpha creates the session and starts booting its machine at once, while your message is still on its way. While the session is being created, a second Enter does nothing, so you never get two sessions by accident.
2
Watch the session open
The home screen dissolves into the session’s layout, and the composer glides down to the bottom of the chat. Your message appears straight away as your bubble at the top of the transcript, and the header already carries the session’s name: at first, the opening of your message. If sending takes more than a second, “Sending…” shows under the bubble. Browsers without view transitions, and systems set to reduce motion, skip the animation.
Your message sits at the top, with the agent's first reply and the working line under it.
3
Let your files upload
Attached files wait for the machine, then upload into /workspace/uploads/. Meanwhile a status line directly above the composer reads “Uploading 2 files…”, with a seconds counter after three seconds. Each file adds a line such as [Attached file: uploads/class-schedule.csv (12.4 KB)] to your message, so the agent knows where to look. Images up to 15 MB also reach the model as pictures it can see. Files and uploads covers attaching more later.
4
Follow the first turn
The machine boots from a ready image in about a second, with the agent already warm inside it. Repositories you chose are cloned before the turn begins; a setup starts with them in place. While the agent works, a pixel loader shows a rotating word such as “Thinking…” or “Striking while hot…” and counts the seconds. Then the transcript streams commands, edits and messages live; Follow the agent’s work explains each part. Until the machine is up, the files panel reads “Sandbox is loading…” and workspace tabs that read from the machine, such as Preview and Database, show grey placeholder bars. They fill in by themselves once it is running.
A first message that is a command, such as /init, opens the session with the command as a chip instead of a bubble. The status line reads “Starting the machine…” until the agent takes the command. With files attached, it reads “Uploading 2 files…” first, then “Handing /init to the agent…”.
A session’s name changes twice in its first moments, then stays put until you change it.
When
The name
Example
When the session is created
”New session”, or the name you gave it with /rename
New session
As the first message lands
The first 60 characters of that message
Build a class-booking web app for Harbor Sailing School. Sho
Shortly after
A short name of two to five words in Title Case
Harbor Sailing Classes
The short name replaces the 60-character one only if nobody has renamed the session in the meantime. A name you set with /rename on the home screen is never replaced. To rename a session later, use Rename in its ⋯ menu in the sidebar.
If new sessions keep the first 60 characters of their first message as their name, short names aren’t turned on for your Alpha.
The header runs across the top of the chat. It tells you which session you’re in, what runs it and what it has cost so far.
In a narrow chat column, the header keeps the title and the agent's mark.
Element
What it tells you
Title
The session’s name, cut short when the chat column is narrow. Hover to read it in full.
Agent badge
The mark and name of the agent, Codex or Claude Code. When the chat column is narrow, only the mark shows. Its tooltip reads “This session runs Codex. A session keeps its agent for life — start a new one to use another.” See Choose the agent and model.
Setup badge
The setup the machine was prepared from. It appears only on sessions started from one, and reads “deleted setup” once that setup is gone.
Cost so far
What the session has spent, in US dollars. ”≈ ” in front means the figure is estimated. Click it (“Open usage”) for the usage dashboard. It hides when the chat column is narrow.
View-only badge
Takes the place of the cost in a session someone shared with you.
When the workspace is hidden, the right of the header also holds the + menu (Add a tab), the GitHub and Share buttons, Show workspace and Show files. While the workspace is showing, press ⌘⇧B to fold the chat away and give the workspace the whole window. Press it again, or click Show chat at the left of the workspace’s tab row, to bring the chat back. Use Ctrl instead of ⌘ on Windows and Linux. Every shortcut is listed in Keyboard shortcuts.
Each session lives at a permanent address, /s/{code}, where the code is 16 random characters. The address bar follows the session you have open, so you can bookmark it or paste it into another tab. The same address is the session’s share link. Until you share the session, only you and your Alpha’s admins can open it.
To
Do this on a session in the sidebar
Open it in a new tab
⌘-click, or middle-click
Open it in a new window
⇧-click
Open it here
Click
Several sessions can work at the same time, each on its own machine, so a second tab is a good way to run two jobs side by side.
A start can fail in two places. Neither loses what you typed.
Where it failed
What you see
What to do
Creating the session
You stay on the home screen with your prompt and files back in the composer. The error shows in red near the top of the page.
Read the error, click it to dismiss it, and press Enter again.
Sending the first message
The session opens with your message back in its composer, and the error shows in red.
Fix what the error names, then press Enter to send it again.
A message longer than 100,000 characters is refused with “prompt too large”; attach the long text as a file instead. For other messages and their fixes, see Troubleshooting and FAQ.
