Does ApiGateway WebSocket Splits Messages at 4 KB?

Hi AWS,

Here is the context:

I have a websocket on api gateway. What it does is acting like a proxy, exchanging messages between different clients( UI and embedded systems). I'm generating some payload from the browser (Client A) and send it using method ApiGatewayManagementApiClient::PostToConnectionCommand via Lambda to the receiver's ConnectionID (Client B). I expect when the receiver (Client B) gets the payload to generate a response. It has been tested to work fine with short payloads less than 4 KB. But it would crash Client B when I send a payload larger than 4KB from the UI. It is likely because the websocket lib in clientB is not capable of handling fragmented message. According to AWS documentation they have a maximum frame size of 32 KB. My full message is around 5~6 KB, so I expect that it is going to be sent at once. Unfortunately this doesn't seem to be the case my message is split to 4 KB fragments.

So my question is: Is it possible that AWS API Gateway is splitting my message in 4KB chunks (or Lambda does it) and if it is so is it possible to somehow increase this limit so I receive the whole message at once instead?

Any help will be appreciated.