diff --git a/docs/IMAGE_STREAM.md b/docs/IMAGE_STREAM.md
index 5ef3def3..fb5cd606 100644
--- a/docs/IMAGE_STREAM.md
+++ b/docs/IMAGE_STREAM.md
@@ -57,6 +57,7 @@ ACK handling is mandatory for correct operation:
 - `END` **must** be acknowledged (`ack_for=END`) on each socket for successful completion.
 - `CANCEL` is acknowledged during rollback paths.
 - `DATA` **must** be ackonwledged for every frame and should be used to report fatal downstream errors immediately.
+- `CALIBRATION` not acknowledged at this moment.
 
 On Linux, large payload transmission can use kernel TCP zero-copy (`SO_ZEROCOPY`/`MSG_ZEROCOPY`) when enabled; below threshold or when unavailable, transfer falls back to normal `send()` behavior.