Constant MAX_BLOCKS_IDS_IN_CHAIN_ENTRY 

pub const MAX_BLOCKS_IDS_IN_CHAIN_ENTRY: usize = 25_000;

The maximum amount of block IDs allowed in a chain entry response.

ref: https://github.com/monero-project/monero/blob/cc73fe71162d564ffda8e549b79a350bca53c454/src/cryptonote_config.h#L97