Alnylam Pharmaceuticals [ALNY] — Trade Construction & Risk

2026-07-29 · framework: Criteria, 2026-07-29

This document issues no position verdict. It states what a position would have to look like if a book chose to take one, what would invalidate the analysis, and what the actual tradable instruments are. The capital decision belongs to portfolio-book, not here.

1. Vehicle — the chain was pulled, not assumed

criteria.md, Liquidity Criteria: "Any proposed options structure requires the actual chain pulled first — open interest and quoted size for the specific strikes and expiry." Pulled from Alpaca on 2026-07-29.

Common stock — viable

Exit in a stressed tape at 20% of ADV is one to two days for $10m. PASS.

Options — not viable at institutional size, and this is the finding

January 2027 calls (166 days), spot $288.50:

March 2027 calls: total open interest across the entire $260–400 range is 326 contracts, maximum 116 at any single strike.

Assessment. Open interest exists at two January strikes, but quoted size is 1 to 17 contracts and the spread on the most-liquid strike is 10.4% of mid. A 280/370 January call spread — the structure the delta profile would suggest — requires crossing roughly 30% of mid in round-trip friction. Any structure above approximately 50 contracts (~$225k of notional delta) cannot be filled at quoted size. This is the HCA failure mode (maximum 18 contracts across an entire chain) in a milder form, and the conclusion is the same: a vehicle that cannot be filled is not a vehicle.

Implied volatility is 48–53% against 42% realised. Long premium is being sold expensive here. That is a second, independent reason the options route is unattractive even at a size it could absorb.

If a position is taken, the vehicle is the common stock. No options structure is recommended and none is appended to trade_recommendations.jsonl.

2. Sizing inputs (the book computes the size; these are the inputs)

criteria.md on the Downside Criteria: "Inverse-volatility sizing is the active protection, and it works because a fat-left-tail name is almost always a high-volatility name and is sized down automatically." ALNY at 42% realised is sized down automatically relative to a 20% name. That is the intended mechanism and no separate cap is asserted.

3. Entry timing — what Momentum Criteria says, and what it does not

Momentum is MEASURED. It governs when, never whether.

Read. The name is 41.3% below its 52-week high, in the second momentum quintile, below its 200-day, with RSI at neutral. Revenue is guided +49% and the EV/sales multiple sits at the 2nd percentile of its own 4.5-year range. That is a de-rated grower, not a broken one — the multiple has compressed by roughly 60% from its 2022–2023 norm while the revenue base has quadrupled.

Timing implication, not a veto. A book that scales in rather than taking a full position at once is acting consistently with a 38th-percentile momentum reading. The natural scaling checkpoint is dated: Q2-2026 results, expected late July / early August 2026 (see the calendar — the date is not yet announced and is flagged as expected, not confirmed).

Any language in which momentum blocks or vetoes this name is deleted. Under the retired numbering this was Gate 6, and its demotion to MEASURED is the type-discipline test case in criteria.md.

4. Invalidation — dated, falsifiable, and specific

These are the conditions under which the analysis in this memo is wrong, not the conditions under which the price falls.

What is explicitly not an invalidation. A drawdown. ALNY has 42% realised volatility; a 25% decline is roughly a one-standard-deviation half-year move and carries no information about the mechanism. The Downside Criteria is about permanent impairment, not volatility.

5. Downside Criteria — logged for the ledger

Per criteria.md, the bear case, its probability and its named cause are logged on every name so that ledger_scorer.py can Brier-score them.

Honest note on the bear case, since criteria.md records the principal's objection that bear cases are often used "without much backbone or rigorousness … to exclude good investments": the economic bear case here does not produce a loss at this price. I have said so rather than manufacturing one. The only case that impairs capital permanently is a scientific event, and I have given it a probability rather than a paragraph.

6. Position construction, if a book takes one

Stated conditionally. The memo does not decide this.

7. What a book should watch that this memo cannot resolve

1. Consensus. No Street numbers were obtainable (Alpha Vantage quota exhausted by parallel agents). The house-versus-Street question — the one the Consensus Criteria exists to answer — is INDETERMINATE. If the Street is already at $5.1bn for FY2026 and $7.0bn for FY2027, the 12-month target here is a consensus target and not a variant view. That is unknown and is not guessed at.
2. The competitive read on acoramidis. ALNY's own corpus is silent (zero mentions in fourteen quarters). BridgeBio's own disclosures are the place to resolve this and were outside this run's scope.
3. The blended royalty rate payable on AMVUTTRA. Disclosed to be rising; the rate itself is not given. This is the single largest uncertainty in the terminal-margin assumption.
4. Correlation with the existing book. Not computed here. ALNY's correlation with any existing VRTX, REGN, NBIX or BMRN exposure is a concentration question portfolio-book owns.