GPT-6 Astra · Context
How Many Reference Images Can You Send GPT-6 Astra at Once?
People search for Astra's context window because they want to know how much they can hand it before something quietly gets dropped. For creative work the question is more specific: how many reference pictures fit in one message, and does the model really look at all of them?
On September 20, 2026 we measured it in Ciyo rather than guessing. Ten images went in and all ten came back described correctly. Twenty-four produced a refusal with an exact number in it.
The test
We made ten images that cannot be confused with each other: one flat shape per file, each in its own colour, each with a descriptive file name from ref-01-circle.png to ref-10-arrow.png. Distinct files matter, because a model can bluff its way through ten photographs of the same mug.
Then we attached all ten to a single message and asked for a count, an ordered list, and an explicit statement about anything missing.
I attached a set of reference images. Count them and tell me exactly how many you received. Then list them in the order you received them, and for each one give the shape and the colour in a few words. If any attachment did not reach you, say so.Ten went in and ten came back
Astra replied that it had received exactly ten reference images and inspected all of them, then listed every file by name with the right shape and the right colour, and finished with “All 10 listed attachments reached me; none is missing.”
One detail in the panel is worth noticing: the reply is preceded by four separate “Inspect images” steps. The model did not take all ten in a single glance. It worked through them in batches, which is part of why a request with many attachments feels slower than a plain question.
Ten is the limit, and Ciyo says so
We then tried more. Twelve numbered images, and separately twenty-four. Nothing was silently dropped and nothing was summarised away. The composer refused the attachment outright with a plain sentence: “Attach up to 10 images per message.”
That is the useful kind of limit. A hard refusal tells you where the edge is; a silent truncation would have let us believe the model had seen everything.
Work inside ten on purpose
Ten is more than most jobs need if you choose the ten deliberately. A set of near-duplicates wastes the budget; a spread of genuinely different examples spends it well.
The pattern that works for us is three of style, three of subject, two of layout, one to avoid, and one that is the real thing you are matching. Name the role of each one in the message rather than hoping the model infers it.
| Slot | How many | What it is for |
|---|---|---|
| Style | 3 | Colour, texture and finish you want to copy |
| Subject | 3 | The object or scene itself, from different angles |
| Layout | 2 | Where things sit in the frame and where the empty space is |
| Counter-example | 1 | Something you explicitly do not want |
| The real one | 1 | The actual product, logo or photograph being matched |
When ten is genuinely not enough
Split the work rather than fighting the limit. Send the first ten, ask for a written summary of what the model took from them, then start the next message with that summary plus the next ten. The summary carries the information forward as text, which costs far less than pictures.
For a long job, save the summary somewhere you control. A thread can be reloaded, a browser tab can be closed, and a paragraph you wrote down survives both.
Other tools publish their own numbers
Limits like this are normal and they differ per tool. On September 15, 2026 someone in r/comfyui asked how to add more image input slots to a node and quoted its documented allowance: up to nine reference images, with a maximum of twelve total media inputs.
That is a different product with different numbers, and we cite it only to make the point that the number is a product decision, not a law. Ciyo's is ten per message, measured today.
Posted 2026-09-15, about a different tool. It quotes that tool's own limit, not Ciyo's.
Reference image questions
Does the model really look at every attachment?
In our ten-image run it did, and it listed all ten correctly by file name. The panel showed four separate inspection steps, so it read them in batches rather than at once.
What happens if I attach more than ten?
The composer refuses with the message Attach up to 10 images per message. Nothing is silently dropped, which is the behaviour you want.
Do reference images cost credits?
The message itself was not charged in our session. The cost of attachments shows up as time rather than credits: more pictures means more inspection steps before any answer.
Put your ten references to work
Choose ten that differ on purpose, name what each one is for, and let Astra tell you what it took from them.