Mariner's $1.7B Q4 2025 13F: 65 New Positions and a Mega-Cap Rebuild

MARINER INVESTMENT GROUP LLC filed a Q4 2025 13F showing $1.71B in reported value, and the most interesting detail is not just the size. It is the shape of the repositioning: Mariner did not just refresh the edges of the book. It rebuilt the core around large-cap compounders and semiconductor infrastructure, which is a far more aggressive signal than a routine rebalance.

TL;DR

• Reported AUM: $1.71B across 111 holdings.
• Top holding: MICROSOFT CORP (MSFT) at 9.7% of the portfolio.
• Fresh activity: 65 new positions and 8 complete exits versus Q3 2025.
• Biggest increase: CRWV rose 1250% quarter over quarter.
• Biggest decrease: FERG fell 91% quarter over quarter.
• Whale Score: 84.50, which keeps this manager firmly in the upper tier of institutional quality screens.
• Key read-through: Mariner did not just refresh the edges of the book. It rebuilt the core around large-cap compounders and semiconductor infrastructure, which is a far more aggressive signal than a routine rebalance.

Filing Snapshot

What Changed

The headline holdings already tell the story. This was a quarter built around MICROSOFT CORP (MSFT), LAM RESEARCH CORP (LRCX), ALPHABET INC (GOOG), COSTCO WHSL CORP NEW (COST), ISHARES BITCOIN TRUST ETF (IBIT). For a manager this large, concentration at the top matters more than the 80th position because the top sleeve is where the real view shows up.

Compared with Q3 2025, the filing shows 65 fresh entries and 8 full exits. That matters because broad turnover in a mega-book usually signals a screen change, a risk-budget change, or both. It is usually too large to dismiss as cash management noise.

The most aggressive increase among overlapping names was CRWV, up about 1250% quarter over quarter. That kind of move usually means the manager wanted a cleaner expression of a theme rather than a passive carry-over.

On the other side, FERG was cut hardest. These sharp reductions often matter as much as new buys because they reveal which exposures lost priority when capital had to be reallocated.

Why It Matters

Mariner did not just refresh the edges of the book. It rebuilt the core around large-cap compounders and semiconductor infrastructure, which is a far more aggressive signal than a routine rebalance. For retail readers, the practical takeaway is to focus on the positions that sit near the top of the portfolio and on the names that changed by triple-digit percentages. That is where the signal is strongest.

This is also why comparing managers like Vanguard, BlackRock, and MARINER INVESTMENT GROUP LLC can be so useful. Passive giants tell you what broad market ownership looks like. A filing like this tells you where a more opinionated allocator is choosing to be different.

What Analysts Might Misread

The easiest mistake is to treat every large disclosed position as a fresh bullish call. That is not always true. Some large positions are inherited, benchmark-aware, or tax-managed. The better way to read this filing is to separate stable core weights from names where size changed abruptly.

Questions Investors Are Really Asking

What did MARINER INVESTMENT GROUP LLC buy in Q4 2025?

The biggest disclosed additions centered on MSFT, LRCX, GOOG, with 65 new positions overall in the filing.

What is the biggest position in MARINER INVESTMENT GROUP LLC's Q4 2025 13F?

MICROSOFT CORP was the largest disclosed holding at about 9.7% of the reported portfolio.

Did MARINER INVESTMENT GROUP LLC become more concentrated in Q4 2025?

The filing suggests a more opinionated book around the top holdings, with the five largest positions accounting for roughly 36.0% of reported value.

Why does this Q4 2025 filing matter?

Mariner did not just refresh the edges of the book. It rebuilt the core around large-cap compounders and semiconductor infrastructure, which is a far more aggressive signal than a routine rebalance.