Ask an agent on a Saturday where the SPY walls are and it will give you two strikes. They may be correct. They describe the options market as it stood at the last session, because that market is shut. An agent that says so has given you a sound answer. One that leaves it out has let you think the reading is live.
A model does not know what day it is
A model has no clock of its own. It may be told the date by the app, or it may not. Even with the date, it does not reliably work out whether the cash market is open. So the knowledge has to come from the data. The time on the reading is the evidence.
What the payload tells it
Every NoVo reading carries as_of and age_seconds. The free dealer levels also carry an age in minutes and a delayed flag. During the session, the age is small and steady. Over a weekend, the reading’s time sits at the last session and the age is large. An agent that reads the stamp can say plainly that the levels are from Friday’s session.
Closed is not stale
A large age over a weekend is expected. Nothing is broken. The source market is shut, and the last reading is the latest there is. A large age in the middle of a session is a different matter and may mean a feed has stopped. The agent should tell these apart, using the day and the hour. The distinction is drawn in delayed data and stale data.
What still moves
Some markets do not close. Crypto trades all week. So do the stock and index perps on Hyperliquid’s builder books. With a paid key, get_stocks_onchain returns the index perps’ move since the last cash close. A good weekend answer has two parts. The dealer levels, labeled as the last session’s. The perp move, labeled as a market price on another venue, live now. What that second reading is worth is covered in a stock perp when the cash market is closed.
The agent must not join them into a forecast. Levels from Friday and a perp price from Sunday do not add up to Monday’s open.
Other traps after hours
A stock token’s quote goes wide outside market hours. The midpoint of a very wide quote is not a price. If the agent reports a token price while the market is shut, it should give the bid and the ask. The quotes tool has its own version of this. Some of its index rows are futures, which trade overnight when the cash index does not.
The regular cash close is 4:00pm Eastern. On an early close it is 1:00pm. An agent working from habit may assume the usual bell. It should take the session’s end from the reading’s time and not from its own assumption. Holidays are handled in the implied open on holidays and early closes.
The instruction
One line: before quoting any reading, check its time, and if the market it comes from is shut, say the reading is from the last session and give that session’s date. Then test it on a Sunday.
Trader shows the implied open only while the cash market is shut, for the same reason. Over the MCP & API, the stamp on each reading carries that information to the agent.