Backsolve is one of the most useful tools in private-company equity valuation. When a financing round is recent, arm’s length, and representative of the security and market being valued, working backward from that observed price calibrates an option-pricing or hybrid model efficiently. The current AI mega-round and mega-tender environment has not broken that logic, but it has stress-tested it. The same enterprise can produce four different observed prices in eighteen months across different securities, different markets, and very different deal settings, and only one or two of them are likely to be the right anchor for any specific common-stock valuation date.
That is where the AICPA’s December 2025 working draft and the SEC staff’s Financial Reporting Manual converge. Transaction evidence matters, but only after the valuation specialist determines what market, what security, and what facts the price actually reflects. The era when a board could point to “the last round” and stop the analysis there has ended. The companies that have made that the most visible are the AI leaders.
OpenAI in eighteen months
Anthropic at the other extreme
OpenAI shows price proliferation across security types. Anthropic shows a different stress: extreme operating velocity between transaction dates. On February 12, 2026, Anthropic announced a $30 billion Series G at a $380 billion post-money valuation, disclosing $14 billion in run-rate revenue, more than 500 customers spending over $1 million annualized, and over $2.5 billion of run-rate revenue from Claude Code alone. By April 2026, Anthropic announced run-rate revenue had surpassed $30 billion and the over-$1M-annualized customer count had doubled to more than 1,000.
A February price is not necessarily wrong, but it is not self-evidently current by April. Calibration that ignores the velocity between the round and the measurement date stops being calibration and becomes a snapshot stretched past its useful life.
Why the secondary market makes this universal
The AI names are extreme, but the dynamic is not. Carta’s data show 396 tender offers conducted on its platform in 2025, up 62% from 244 in 2024, with nearly 20% from Series E+ companies. Over the twelve months ending June 2025, Carta estimated VC secondary transaction value at $61.1 billion, above the combined value of VC-backed IPOs in the same period. PitchBook’s annual figure for 2025 puts U.S. venture secondary transaction value at roughly $106 billion.
For any late-stage 409A engagement, that’s the new fact pattern: multiple observed prices of the same enterprise, across different securities and markets, often within months of the measurement date. None of those data points is junk, and none of them is automatically dispositive either.
Boards get into trouble when they treat the last round as a verdict rather than as evidence.
Five stress tests for backsolve
What the SEC is asking
Recent comment-letter responses make the discipline visible. In 2025 correspondence, Sionna Therapeutics described its common-stock valuations as using OPM, a market-adjusted approach based on a recent arm’s-length transaction, and a hybrid PWERM/OPM with IPO and trade-sale scenarios. The company then had to reconcile a much higher IPO range to earlier fair-value conclusions by walking through scenario probabilities, DLOMs, and post-valuation milestones. In a March 2025 response, Jade Biosciences described hybrid valuations in which scenario probabilities shifted as a merger and financing became probable.
The staff is not banning backsolve. It is asking issuers to explain why last-round economics are, or are not, representative of current fair value for the shares being valued, which is the question every late-stage 409A board should be ready to answer in writing.
The questions reviewers will ask
- Why is this the right anchor security?
- What rights did that investor receive that common stock does not?
- Is this really the principal market?
- What changed in the business since the round?
- If this was a tender, who set the rules and who benefited?
- Why was OPM chosen instead of PWERM, hybrid, or simulation?
- If the company is preparing for an IPO, how would this conclusion stand up to SEC scrutiny?
The takeaway
In the AI mega-tender era, a transaction price is evidence rather than verdict. The better the round matches the subject security, the principal market, and the measurement date, the more persuasive the backsolve. The more the facts drift into structured terms, strategic motives, insider dynamics, selective secondary liquidity, or explosive operating change, the more the appraiser has to translate the price rather than repeat it. Far from skepticism for its own sake, that translation is what makes the work defensible, and it separates a 409A report that survives audit, board, and SEC review from one that becomes the start of a longer conversation.