The condition for the prediction was effectively met:

• The One Big Beautiful Bill Act (OBBBA), the "big beautiful bill," passed the House on May 22, 2025, the Senate on July 1, 2025, and was signed into law on July 4, 2025.(en.wikipedia.org)
• CBO and independent estimates for both the House version and the enacted law show it raises, not lowers, deficits by roughly $2.8–3.4T over 2025–2034, i.e., there was no net “material fiscal tightening.”(reuters.com)

Chamath’s then-clause was that within 60–90 days of passage, bond markets would “react negatively” by demanding higher yields and/or showing clear stress in Treasury demand relative to prevailing long-term real/nominal rates (~5–5.5% on long bonds at the time).

What actually happened (July–early October 2025):

• Long-dated nominal yields were already near or above 5% before and around House passage and the Moody’s downgrade: the 30‑year hit about 5.15% on May 22 when the House first passed the bill.(webull.ca)
• Around enactment, monthly 30‑year yields were ~4.9%: May 4.90%, June 4.89%, July 4.92%. In the 60–90 days after signing (roughly Sept 2–Oct 2), the 30‑year averaged ~4.7–4.8%, slightly lower than the levels around passage (August 4.87%, September 4.74, October 4.64).(ycharts.com) There was no clear new spike above prior peaks; if anything, yields drifted modestly down from their May–July highs.
• A widely cited Reuters wrap on July 7 explicitly noted that the bond market’s reaction to final passage was “relatively muted” and that the expected deficit expansion from Trump’s agenda had "already been priced in"; investors were more focused on growth data and Fed policy than on the bill itself.(reuters.com)

Auction / demand stress evidence:

• There was a weak 20‑year auction and a sharp jump in long yields before final passage (May 21–22), reflecting concerns about fiscal policy and the Moody’s downgrade.(wsj.com) Those events predate the 60–90‑day post‑enactment window Chamath pointed to.
• Inside and around the window, the picture is mixed rather than clearly “crisis-like.” For example, an August 21 30‑year TIPS reopening cleared at a very high real yield of 2.65% (a 24‑year high) but with strong demand (bid‑to‑cover 2.78, yield stopping through when‑issued), which is the opposite of an impaired auction.(tipswatch.com)
• Some analyses in late September describe general auction strains (lower bid‑to‑cover, wider tails, waning foreign demand), but they tie this to the broader combination of heavy issuance, drained Fed reverse‑repo balances, and global fiscal worries—not to a discrete, new repricing of U.S. risk specifically in the 60–90 days after OBBBA’s enactment.(universalvalueadvisors.com) Other auctions (e.g., the September 10‑year note) actually showed strong demand and a stop‑through yield, again undercutting the notion of clear, generalized stress in that specific window.(streetinsider.com)

Putting this together:

• The bill did become law with overall fiscal loosening, so the condition trigger was satisfied.
• By 60–90 days after enactment, long-term yields were not meaningfully higher than at passage or the pre‑passage peak; they were marginally lower.
• Auction results in that interval show pockets of strain but also episodes of very strong demand, not an unambiguous negative repricing that would make it obvious “in the next 60 to 90 days” that markets had re‑underwritten U.S. fiscal risk at even higher required yields.

Given the time‑bound and directional nature of Chamath’s forecast (a distinct, clearly negative bond-market reaction after the bill became law), the realized data don’t match it. The structural fiscal concerns he highlighted are real and widely discussed, but the specific prediction about how and when bond markets would respond is not borne out by yields or auction behavior in that 60–90‑day window.