diff --git a/src/inspect_ai/util/_sandbox/environment.py b/src/inspect_ai/util/_sandbox/environment.py
index ba32bb4502..25746d58b1 100644
--- a/src/inspect_ai/util/_sandbox/environment.py
+++ b/src/inspect_ai/util/_sandbox/environment.py
@@ -118,7 +118,15 @@ async def exec(
         The current working directory for execution will be the per-sample
         filesystem context.
 
-        By default, each output stream (stdout and stderr) is limited to 10 MiB. You can override this by setting the `INSPECT_SANDBOX_MAX_EXEC_OUTPUT_SIZE` environment variable (specified in bytes). If exceeded, an `OutputLimitExceededError` will be raised.
+        By default, each output stream (stdout and stderr) is limited to 10 MiB. You can override this by setting the `INSPECT_SANDBOX_MAX_EXEC_OUTPUT_SIZE` environment variable (specified in bytes).
+
+        Behaviour above this limit depends on the sandbox provider. A provider may
+        raise `OutputLimitExceededError`, or return only the trailing portion of
+        the output with the beginning discarded. Callers should therefore not
+        assume that returned output is complete or rely on an exception to detect
+        overflow. This is particularly important when parsing structured output
+        such as JSON. For large output, write to a file and use `read_file()`,
+        which always raises `OutputLimitExceededError` when the limit is exceeded.
 
         Args:
           cmd: Command or command and arguments to execute.
@@ -145,7 +153,7 @@ async def exec(
             characters which cannot be decoded.
           PermissionError: If the user does not have
             permission to execute the command.
-          OutputLimitExceededError: If an output stream
+          OutputLimitExceededError: May be raised if an output stream
             exceeds the limit.
         """
         ...