Which holdings were largest in PRIMECAP's Q4 2025 filing?

The largest disclosed holdings were LLY ($9.96B), MU ($7.08B), GOOGL ($4.74B), MSFT ($3.52B), and KLAC ($3.49B).

How concentrated was PRIMECAP in Q4 2025?

Top-1 concentration was 7.5%, top-5 was 21.8%, and top-10 was 33.4%.

What does the AUM trend suggest for PRIMECAP?

It suggests a steady recovery: from $120.96B in 2025Q1 to $132.11B in 2025Q4.

Are 'NEW position' labels reliable proof of fresh buys in this extract?

Not necessarily. For large-filer datasets they can be artifacts and should be validated with quarter-over-quarter position change analysis.

Research

PRIMECAP's $132.11B Q4 Setup: Healthcare-Semiconductor Barbell Gets Heavier

Q: What was PRIMECAP's 13F AUM in Q4 2025?

PRIMECAP reported $132.11B in canonical 13F assets for 2025Q4.

PRIMECAP reported $132.11B in Q4 2025 with Eli Lilly and Micron alone at 12.9% combined, signaling a barbell between healthcare defensiveness and semiconductor cyclicality.

By Marcus Chen, Senior Market Analyst

PublishedMarch 22, 2026UpdatedMarch 23, 2026

PRIMECAP’s Q4 2025 filing highlights a clear two-engine thesis: healthcare quality plus semiconductor upside. The firm ended the quarter at $132.11B with 319 positions, led by Eli Lilly (LLY) at $9.96B and Micron (MU) at $7.08B.

TL;DR

Canonical AUM: $132.11B in 2025Q4.
Top pair concentration: LLY (7.54%) + MU (5.36%) = 12.90% combined.
Overall concentration: Top-1 7.5%, top-5 21.8%, top-10 33.4%.
Largest names after top two: GOOGL ($4.74B), MSFT ($3.52B), KLAC ($3.49B).
AUM trend: Recovered from $120.96B in ’25 Q1 to $132.11B in ’25 Q4.
Read-through: PRIMECAP looks like it is adding cyclical growth participation without abandoning quality anchors.

Filing Snapshot

Manager: PRIMECAP Management Co/CA/
Quarter: 2025Q4
Canonical AUM: $132.11B
Positions: 319
WhaleScore: 72.25

The top book expresses a healthcare + semis barbell

PRIMECAP’s lead position in LLY is a classic quality-growth healthcare anchor. The second-largest line, MU, adds a more cyclical semiconductor beta profile. The next group—GOOGL, MSFT, and KLAC—keeps the portfolio tilted toward large-cap platform and chip-cycle exposure.

As with other large 13F extracts, the raw “NEW position” labels in API outputs are not treated here as confirmed initiations; they can be artifacts without full filing-to-filing reconciliation.

AUM recovery is steady, not explosive

The AUM path shows drawdown and repair: $138.13B in ’24 Q2 down to $120.96B in ’25 Q1, then back up through $126.19B (’25 Q2), $130.57B (’25 Q3), and $132.11B (’25 Q4). This is consistent with deliberate re-risking rather than a one-quarter chase.

Why this filing matters

PRIMECAP remains one of the cleaner examples of concentration with control: meaningful conviction in the top book, but still enough diversification across 319 positions to avoid single-theme fragility. For investors tracking institutional style persistence, this is a strong continuity signal.

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Q&A

What was PRIMECAP’s 13F AUM in Q4 2025?

PRIMECAP reported a canonical 13F AUM of $132.11B in 2025Q4.

What are PRIMECAP’s largest disclosed holdings?

The top disclosed positions are LLY ($9.96B), MU ($7.08B), GOOGL ($4.74B), MSFT ($3.52B), and KLAC ($3.49B).

How concentrated is the portfolio?

Top-5 concentration is 21.8% and top-10 concentration is 33.4%.

Did PRIMECAP recover from its 2025Q1 drawdown?

Yes. AUM rose from $120.96B in 2025Q1 to $132.11B in 2025Q4.

Can I read “NEW position” markers as true new buys?

Not on their own. For large filers, these markers can be extraction artifacts and should be validated using dedicated position-change comparisons.

Marcus ChenSenior Market Analyst

Senior Market Analyst at 13F Insight. Covers institutional portfolio strategy, 13F filings, and smart money trends.