Evidence shows the specific April 2021 Biden proposal to raise the top federal long‑term capital gains tax rate itself to 39.6% was never enacted.

• In April 2021, the Biden administration proposed nearly doubling the top long‑term capital gains rate for high‑income taxpayers from 20% to 39.6%, as part of the American Families Plan.
• Subsequent major tax legislation under Biden—most notably the Inflation Reduction Act of 2022—did not raise the statutory long‑term capital gains rate to 39.6%. Instead, changes focused on corporate minimum taxes, stock buyback excise tax, and IRS enforcement, leaving the top federal long‑term capital gains rate at 20% plus the 3.8% Net Investment Income Tax for high earners. (Various tax references and IRS guidance through 2023–2025 confirm the top LTCG bracket remains 0% / 15% / 20%, not 39.6%.)
• No later budget or reconciliation package that actually passed Congress adopted a 39.6% capital‑gains bracket; the 39.6% figure remains the top ordinary income rate in some Biden proposals, but capital gains themselves were not converted to that rate in enacted law.

Since Chamath’s prediction was that “It’s not going to pass”—referring specifically to the 39.6% capital‑gains hike—and that precise provision indeed did not become law, the prediction is right.