No, you do not have income when a soft fork of cryptocurrency you own occurs.
A soft fork occurs when a distributed ledger undergoes a protocol change that does not result in a diversion of the ledger and thus does not result in the creation of a new cryptocurrency. Because soft forks do not result in you receiving new cryptocurrency, you will be in the same position you were in prior to the soft fork, meaning that the soft fork will not result in any income to you. This is consistent with the IRS guidance which states that a soft fork does not create taxable income as there is no accession to wealth or receipt of new cryptocurrency.
Sources:
Rev. Rul. 2019-24
Notice 2014-21
Publication 544 (2023)
CCA 202114020
Consequences of Hard Forks, Soft Forks, and Airdrops
