# Water Island Capital LLC 13F holdings

> Latest reported SEC 13F equity book. Teaser: top 10 of 86 long-equity positions.
> CIK 1222765. Latest filing Q1 2026, as of quarter end 2026-03-31. Long-equity book $750.1M.

## Top holdings (teaser)

| # | Ticker | Issuer | Value | % of book | Change |
|---|--------|--------|-------|-----------|--------|
| 1 | n/a | Electronic Arts Inc | $50.9M | 6.8% | Added |
| 2 | n/a | Janus Henderson Group PLC | $47.4M | 6.3% | Added |
| 3 | n/a | Warner Bros Discovery Inc | $44.4M | 5.9% | Added |
| 4 | n/a | Hologic Inc | $42.3M | 5.6% | Added |
| 5 | n/a | TXNM Energy Inc | $39.5M | 5.3% | Added |
| 6 | n/a | Penumbra Inc | $39.4M | 5.3% | New |
| 7 | n/a | Chart Inds Inc | $39.3M | 5.2% | Added |
| 8 | n/a | Norfolk Southn Corp | $38.5M | 5.1% | Added |
| 9 | n/a | Masimo Corp | $34.5M | 4.6% | New |
| 10 | n/a | Webster Finl Corp | $28.9M | 3.8% | New |

## Latest moves

Bought: Penumbra Inc, Masimo Corp, Webster Finl Corp
Sold: Air Lease Corp, Clearwater Analytics Hldgs I, Sealed Air Corp New

Counts and totals reflect the 13F filers and securities Arkolith tracks, not the entire institutional universe. Option legs are excluded from the book above.

## Full data via the API and MCP

This page is a teaser. The complete book, full quarter-over-quarter history, and per-datapoint
provenance are available through the metered REST API and MCP server.

- Endpoint: https://arkolith.com/api/mcp (transport: streamable-http)
- Auth: Bearer API key. Mint one and copy a ready-to-paste command at https://arkolith.com/connect
- Claude Code: `claude mcp add --transport http arkolith https://arkolith.com/api/mcp --header "Authorization: Bearer YOUR_API_KEY"`
- Discovery: `tools/list` is free; `tools/call` is metered by credits.

### Machine-readable
- Tool catalog JSON: https://arkolith.com/api/mcp/catalog
- MCP descriptor: https://arkolith.com/.well-known/mcp.json
- OpenAPI 3.1 REST spec: https://arkolith.com/openapi.json
- Full LLM guide: https://arkolith.com/llms-full.txt
- Human docs: https://arkolith.com/docs

## Source and method

- Source: SEC EDGAR 13F-HR (public domain). Long-equity positions only (option legs excluded). Filed quarterly, about a 45-day lag.
- Primary source: https://www.sec.gov/Archives/edgar/data/1222765/000122276526000007/xslForm13F_X02/primary_doc.xml
- Human page: https://arkolith.com/fund/water-island-capital-llc-1222765
- Per-datapoint lineage: call the `provenance.get` MCP tool for the source URL and fetch history behind any figure.

Paid product with a one-time evaluation grant at signup (no card to evaluate). Most calls cost 1 credit (~$0.01); heavier point-in-time / cross-source tools cost more.

_Latest disclosed public filings. Data, not investment advice._