Transaction version 2 - bytes between tx version and number of inputs In the bitcoin transaction version 2, there are additional two bytes (hex: "0001") between transaction version (hex: "02000000"), and number of inputs (hex: "01"). What it is?

Here's an example https://btc-explorer.com/tx/4f692e7fb63256e4e741b952935e929ad545838d3697c5ee3f044a250c45fb4a

transaction hex: "020000000001010000000000000000000000000000000000000000000000000000000000000000ffffffff4b031a0608048187145b622f4254432e434f4d2ffabe6d6dec50b9ca7f0e6731e89a2516f3df5fd7d65462ed2e68df7bf8e375232b7b28c701000000000000006200de217cb2aaea00000000ffffffff0212b0bf4a000000001976a91478ce48f88c94df3762da89dc8498205373a8ce6f88ac0000000000000000266a24aa21a9ed89dbbf72d51df862d19e0baa551d87e69b65a452496ec9d8203de66c754c30330120000000000000000000000000000000000000000000000000000000000000000000000000"
That is not something specific to version 2 transactions.

What you are looking at are the marker and flag bytes for a segwit transaction. Segwit transactions have a slightly different transaction format which is specified in BIP 144.