Constant BIG_FILE_THRESHOLD 

pub const BIG_FILE_THRESHOLD: usize = _; // 10_485_760usize

Files larger than this use upload.saveBigFilePart - Telegram protocol spec. MUST be 10 MB, not 30 MB. Upload-only: GetFile has no small/big distinction, so this never applies to downloads. See DOWNLOAD_CONCURRENT_THRESHOLD for the download-side equivalent.