As of yesterday, the IRS no longer allows cross-wallet/cross-account cost basis accounting. Each wallet or custodial account has its own cost basis for capital gains tax calculations.

This is an attack of Bitcoin fungibility for white-market usage. It was burdensome enough to track cost basis for accounting before, but now, to be compliant, you ALSO have to track every self-transaction (withdrawing from exchange, wallet-to-wallet, etc.)

https://bitcoin.tax/blog/irs-rev-proc-2024-28-preparing-2025-crypto-reporting-requirements/