Western Digital Corporation
MX ˙ BMV ˙ US9581021055
SecurityMX:WDC / Western Digital Corporation
InstitutionUBS Group AG
Latest Disclosed Ownership4,182,454 shares
Latest Disclosed Value $ 1,131,311,982
UBS Group AG ownership in WDC / Western Digital Corporation

On May 5, 2026 - UBS Group AG filed a 13F-HR form disclosing ownership of 4,182,454 shares of Western Digital Corporation (MX:WDC) valued at $1,131,311,982 USD as of March 31, 2026. The entity filed a previous 13F-HR on January 29, 2026 disclosing 4,550,821 shares of Western Digital Corporation. This represents a change in shares of -8.09% during the quarter.

UBS Group AG has a history of taking positions in derivatives of the underlying security (WDC) in the form of stock options. The firm currently holds call options representing 391,294 of underlying shares valued at $105,841,114 USD and put options representing 100,500 of underlying shares valued at $27,184,245 USD .

Note: prior versions of this page mistakenly stated that the share values represented the number of options, not the number of underlying shares. For more information on the data backing these reports, please see the SEC document Frequently Asked Questions About Form 13F.

Institutional Ownership: 13F and NPORT Filings

The Security and Class in the table below are shown exactly as filed by the investor. We do our best to track continuity of investments through acquisitions, and this will be reflected in the table as changes in names. In addition to descriptive data, performance of the investment is shown over time. To calculate quarterly performance, we first calculate cost basis of the shares purchased during the quarter, then use that to calculate gross profit. Quarterly return is Gross Profit / Starting Portfolio value.

Note that cost basis is calculated and stored in thousands, so small quarterly changes in shares frequently result in a cost basis of zero.

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Institutional Put/Call Ratios
(Premium Subscription Required)

In addition to reporting standard equity and debt issues, institutions with more than 100MM assets under management must also disclose their put and call option holdings. Since put options generally indicate negative sentiment, and call options indicate positive sentiment, we can get a sense of the overall institutional sentiment by plotting the ratio of puts to calls. The chart to the right plots the historical put/call ratio for this instrument.

Using Put/Call Ratio as an indicator of investor sentiment overcomes one of the key deficiencies of using total institutional ownership, which is that a significant amount of assets under management are invested passively to track indices. Passively-managed funds do not typically buy options, so the put/call ratio indicator more closely tracks the sentiment of actively-managed funds.

MX:WDC / Western Digital Corporation Historical Put/Call Ratio
Disclosed Equity Positions (from 13F/NPORT Filings)
File
Date
Effective
Date
Form Security Class ID Avg Price
Paid (Est)
Reported
Shares
ΔShares ΔShares
(%)
Reported
Value
(x1000)
ΔValue
(%)
Alloc
(%)
ΔAlloc ΔAlloc (%) Cost Basis
(x1000)
Unrealized
Gain/Loss
(x1000)
2026-05-05 2026-03-31 13F WESTERN DIGITAL COM 958102105 4,182,454 -368,367 -8.09 1,131,312 44.31 0.0317
2026-01-29 2025-12-31 13F WESTERN DIGITAL COM 958102105 4,550,821 -2,779,175 -37.92 783,970 -10.92 0.1271
2025-11-13 2025-09-30 13F WESTERN DIGITAL COM 958102105 7,329,996 -4,097,220 -35.85 880,039 20.35 0.1379
2025-08-14 2025-06-30 13F WESTERN DIGITAL COM 958102105 11,427,216 -5,662,033 -33.13 731,228 5.83 0.1266
2025-05-13 2025-03-31 13F WESTERN DIGITAL COM 958102105 17,089,249 8,999,414 111.24 690,918 43.23 0.1270
2025-02-14 2024-12-31 13F WESTERN DIGITAL COM 958102105 8,089,835 1,776,784 28.14 482,397 11.89 0.0892
2024-11-14 2024-09-30 13F WESTERN DIGITAL COM 958102105 6,313,051 -144,983 -2.25 431,118 -11.90 0.0939
2024-08-14 2024-06-30 13F WESTERN DIGITAL COM 958102105 6,458,034 387,858 6.39 489,325 18.13 0.1209
2024-05-13 2024-03-31 13F WESTERN DIGITAL COM 958102105 6,070,176 327,091 5.70 414,229 37.72 0.1032
2024-02-09 2023-12-31 13F WESTERN DIGITAL COM 958102105 5,743,085 82,007 1.45 300,765 16.43 0.0900
2023-11-09 2023-09-30 13F WESTERN DIGITAL COM 958102105 5,661,078 3,646,286 180.98 258,315 238.01 0.0890
2023-08-11 2023-06-30 13F WESTERN DIGITAL COM 958102105 2,014,792 -1,732,112 -46.23 76,421 -45.86 0.0258
2023-05-12 2023-03-31 13F WESTERN DIGITAL COM 958102105 3,746,904 -1,050,140 -21.89 141,146 -6.74 0.0516
2023-02-08 2022-12-31 13F WESTERN DIGITAL COM 958102105 4,797,044 708,817 17.34 151,347 13.73 0.0565
2022-11-10 2022-09-30 13F WESTERN DIGITAL COM 958102105 4,088,227 -1,848,491 -31.14 133,073 -50.00 0.0583
2022-08-10 2022-06-30 13F WESTERN DIGITAL COM 958102105 5,936,718 4,345,734 273.15 266,143 236.92 0.1093
2022-05-16 2022-03-31 13F WESTERN DIGITAL COM 958102105 1,590,984 1,044,039 190.89 78,993 121.48 0.0263
2022-02-14 2021-12-31 13F WESTERN DIGITAL COM 958102105 546,945 71,434 15.02 35,666 32.89 0.0102
2021-11-15 2021-09-30 13F WESTERN DIGITAL COM 958102105 475,511 24,601 5.46 26,838 -16.37 0.0085
2021-08-13 2021-06-30 13F WESTERN DIGITAL COM 958102105 450,910 102,542 29.43 32,091 38.01 0.0103
2021-05-12 2021-03-31 13F WESTERN DIGITAL COM 958102105 348,368 -223,785 -39.11 23,253 -26.63 0.0077
2021-02-11 2020-12-31 13F WESTERN DIGITAL COM 958102105 572,153 -51,057 -8.19 31,691 39.12 0.0107
2020-11-12 2020-09-30 13F WESTERN DIGITAL COM 958102105 623,210 150,569 31.86 22,779 9.16 0.0086
2020-07-31 2020-06-30 13F WESTERN DIGITAL COM 958102105 472,641 17,455 3.83 20,867 10.15 0.0088
2020-05-01 2020-03-31 13F WESTERN DIGITAL COM 958102105 455,186 73,744 19.33 18,945 -21.75 0.0089
2020-02-14 2019-12-31 13F WESTERN DIGITAL COM 958102105 381,442 22,076 6.14 24,210 12.96 0.0084
2019-11-14 2019-09-30 13F WESTERN DIGITAL COM 958102105 359,366 -146,618 -28.98 21,432 -10.92 0.0083
2019-08-14 2019-06-30 13F WESTERN DIGITAL COM 958102105 505,984 -165,486 -24.65 24,060 -25.44 0.0093
2019-05-14 2019-03-31 13F WESTERN DIGITAL COM 958102105 671,470 184,653 37.93 32,270 79.30 0.0133
2019-02-14 2018-12-31 13F WESTERN DIGITAL COM 958102105 486,817 -2,149 -0.44 17,998 -37.12 0.0082
2018-11-14 2018-09-30 13F WESTERN DIGITAL COM 958102105 488,966 -44,124 -8.28 28,624 -30.64 0.0113
2018-08-14 2018-06-30 13F WESTERN DIGITAL COM 958102105 533,090 136,501 34.42 41,267 12.77 0.0179
2018-05-15 2018-03-31 13F WESTERN DIGITAL COM 958102105 396,589 -4,019 -1.00 36,594 14.86 0.0158
2018-02-14 2017-12-31 13F WESTERN DIGITAL COM 958102105 400,608 63,897 18.98 31,860 9.51 0.0131
2017-11-14 2017-09-30 13F WESTERN DIGITAL COM 958102105 336,711 -352,849 -51.17 29,092 -52.38 0.0135
2017-11-14 2017-06-30 13F/A-1 WESTERN DIGITAL COM 958102105 689,560 37,236 5.71 61,094 13.48 0.0316
2017-08-14 2017-06-30 13F WESTERN DIGITAL COM 958102105 689,560 37,236 61,094
2017-11-14 2017-03-31 13F/A-1 WESTERN DIGITAL COM 958102105 652,324 85,577 15.10 53,837 39.80 0.0294
2017-05-12 2017-03-31 13F WESTERN DIGITAL COM 958102105 652,324 85,577 53,837
2017-02-14 2016-12-31 13F WESTERN DIGITAL COM 958102105 566,747 125,070 28.32 38,510 49.12 0.0213
2016-11-14 2016-09-30 13F WESTERN DIGITAL COM 958102105 441,677 57,305 14.91 25,825 42.17 0.0154
2016-08-12 2016-06-30 13F WESTERN DIGITAL COM 958102105 384,372 253,744 194.25 18,165 194.36 0.0114
2016-05-12 2016-03-31 13F WESTERN DIGITAL COM 958102105 130,628 -432,338 -76.80 6,171 -81.75 0.0041
2016-02-16 2015-12-31 13F WESTERN DIGITAL COM 958102105 562,966 -216,051 -27.73 33,807 -45.37 0.0219
2015-11-13 2015-09-30 13F WESTERN DIGITAL COM 958102105 779,017 229,242 41.70 61,886 43.54 0.0438
2015-08-14 2015-06-30 13F WESTERN DIGITAL COM 958102105 549,775 -22,590 -3.95 43,113 -17.24 0.0287
2015-05-14 2015-03-31 13F WESTERN DIGITAL COM 958102105 572,365 -287,361 -33.42 52,091 -45.27 0.0360
2015-02-17 2014-12-31 13F WESTERN DIGITAL COM 958102105 859,726 859,726 95,171 0.0665
Disclosed Call Options
File
Date
Effective
Date
Form Security Class ID Opt Avg Share
Price
Shares ΔShares
(%)
Value
(x1000)
ΔValue
(%)
Prior Allocation
(%)
Allocation
(%)
ΔAllocation
(%)
Cost Basis
(x1000)
Profit
(x1000)
Return
(%)
2026-05-05 2026-03-31 13F WESTERN DIGITAL COM Call 391,294 71.54 105,841 169.36 n/a n/a n/a
2026-01-29 2025-12-31 13F WESTERN DIGITAL COM Call 228,100 -24.02 39,295 9.02 n/a n/a n/a
2025-11-13 2025-09-30 13F WESTERN DIGITAL COM Call 300,200 296.04 36,042 643.13 n/a n/a n/a
2025-08-14 2025-06-30 13F WESTERN DIGITAL COM Call 75,800 32.75 4,850 110.14 n/a n/a n/a
2025-05-13 2025-03-31 13F WESTERN DIGITAL COM Call 57,100 -80.58 2,309 -86.83 n/a n/a n/a
2025-02-14 2024-12-31 13F WESTERN DIGITAL COM Call 294,000 -7.84 17,531 -19.52 n/a n/a n/a
2024-11-14 2024-09-30 13F WESTERN DIGITAL COM Call 319,000 179.33 21,785 151.78 n/a n/a n/a
2024-08-14 2024-06-30 13F WESTERN DIGITAL COM Call 114,200 -44.18 8,653 -38.03 n/a n/a n/a
2024-05-13 2024-03-31 13F WESTERN DIGITAL COM Call 204,600 -59.52 13,962 -47.25 n/a n/a n/a
2024-02-09 2023-12-31 13F WESTERN DIGITAL COM Call 505,400 34.02 26,468 53.82 n/a n/a n/a
2023-11-09 2023-09-30 13F WESTERN DIGITAL COM Call 377,100 74.66 17,207 110.12 n/a n/a n/a
2023-08-11 2023-06-30 13F WESTERN DIGITAL COM Call 215,900 14.66 8,189 15.45 n/a n/a n/a
2023-05-12 2023-03-31 13F WESTERN DIGITAL COM Call 188,300 -25.16 7,093 -10.63 n/a n/a n/a
2023-02-08 2022-12-31 13F WESTERN DIGITAL COM Call 251,600 -35.09 7,938 -37.09 n/a n/a n/a
2022-11-10 2022-09-30 13F WESTERN DIGITAL COM Call 387,600 410.00 12,616 270.30 n/a n/a n/a
2022-08-10 2022-06-30 13F WESTERN DIGITAL COM Call 76,000 -39.68 3,407 -45.54 n/a n/a n/a
2022-05-16 2022-03-31 13F WESTERN DIGITAL COM Call 126,000 119.90 6,256 67.41 n/a n/a n/a
2022-02-14 2021-12-31 13F WESTERN DIGITAL COM Call 57,300 -18.14 3,737 -5.42 n/a n/a n/a
2021-11-15 2021-09-30 13F WESTERN DIGITAL COM Call 70,000 3,951 n/a n/a n/a
2021-02-11 2020-12-31 13F WESTERN DIGITAL COM Call 0 -100.00 0 -100.00 n/a n/a n/a
2020-11-12 2020-09-30 13F WESTERN DIGITAL COM Call 70,000 2,559 n/a n/a n/a
2020-05-01 2020-03-31 13F WESTERN DIGITAL COM Call 0 -100.00 0 -100.00 n/a n/a n/a
2020-02-14 2019-12-31 13F WESTERN DIGITAL COM Call 176,500 25.09 11,202 33.12 n/a n/a n/a
2019-11-14 2019-09-30 13F WESTERN DIGITAL COM Call 141,100 -5.93 8,415 17.97 n/a n/a n/a
2019-08-14 2019-06-30 13F WESTERN DIGITAL COM Call 150,000 -6.25 7,133 -7.24 n/a n/a n/a
2019-05-14 2019-03-31 13F WESTERN DIGITAL COM Call 160,000 149.22 7,690 224.06 n/a n/a n/a
2019-02-14 2018-12-31 13F WESTERN DIGITAL COM Call 64,200 2,373 n/a n/a n/a
2018-08-14 2018-06-30 13F WESTERN DIGITAL COM Call 0 -100.00 0 -100.00 n/a n/a n/a
2018-05-15 2018-03-31 13F WESTERN DIGITAL COM Call 15,000 -75.00 1,384 -71.00 n/a n/a n/a
2018-02-14 2017-12-31 13F WESTERN DIGITAL COM Call 60,000 15.61 4,772 6.42 n/a n/a n/a
2017-11-14 2017-09-30 13F WESTERN DIGITAL COM Call 51,900 -84.67 4,484 -85.05 n/a n/a n/a
2017-11-14 2017-06-30 13F/A WESTERN DIGITAL COM Call 338,500 206.33 29,991 228.85 n/a n/a n/a
2017-08-14 2017-06-30 13F WESTERN DIGITAL COM Call 338,500 29,991 n/a n/a n/a
2017-11-14 2017-03-31 13F/A WESTERN DIGITAL COM Call 110,500 36,733.33 9,120 45,500.00 n/a n/a n/a
2017-05-12 2017-03-31 13F WESTERN DIGITAL COM Call 110,500 9,120 n/a n/a n/a
2017-02-14 2016-12-31 13F WESTERN DIGITAL COM Call 300 -98.81 20 -98.65 n/a n/a n/a
2016-11-14 2016-09-30 13F WESTERN DIGITAL COM Call 25,300 -61.26 1,479 -52.07 n/a n/a n/a
2016-08-12 2016-06-30 13F WESTERN DIGITAL COM Call 65,300 -84.52 3,086 -84.52 n/a n/a n/a
2016-05-12 2016-03-31 13F WESTERN DIGITAL COM Call 421,900 18.05 19,931 -7.13 n/a n/a n/a
2016-02-16 2015-12-31 13F WESTERN DIGITAL COM Call 357,400 19,755.56 21,462 14,908.39 n/a n/a n/a
2015-11-13 2015-09-30 13F WESTERN DIGITAL COM Call 1,800 -18.18 143 -17.34 n/a n/a n/a
2015-08-14 2015-06-30 13F WESTERN DIGITAL COM Call 2,200 -98.26 173 -98.50 n/a n/a n/a
2015-05-14 2015-03-31 13F WESTERN DIGITAL COM Call 126,500 4,960.00 11,513 4,056.32 n/a n/a n/a
2015-02-17 2014-12-31 13F WESTERN DIGITAL COM Call 2,500 277 n/a n/a n/a
Disclosed Put Options
File
Date
Effective
Date
Form Security Class ID Opt Avg Share Price Shares ΔShares
(%)
Value
(x1000)
ΔValue
(%)
Prior Allocation
(%)
Allocation
(%)
ΔAllocation
(%)
Cost Basis
(x1000)
Profit
(x1000)
Return
(%)
2026-05-05 2026-03-31 13F WESTERN DIGITAL COM Put 100,500 -64.96 27,184 -44.98 n/a n/a n/a
2026-01-29 2025-12-31 13F WESTERN DIGITAL COM Put 286,800 -14.57 49,407 22.59 n/a n/a n/a
2025-11-13 2025-09-30 13F WESTERN DIGITAL COM Put 335,700 52.45 40,304 186.05 n/a n/a n/a
2025-08-14 2025-06-30 13F WESTERN DIGITAL COM Put 220,200 -2.18 14,091 54.84 n/a n/a n/a
2025-05-13 2025-03-31 13F WESTERN DIGITAL COM Put 225,100 -12.95 9,101 -40.99 n/a n/a n/a
2025-02-14 2024-12-31 13F WESTERN DIGITAL COM Put 258,600 -20.23 15,420 -30.35 n/a n/a n/a
2024-11-14 2024-09-30 13F WESTERN DIGITAL COM Put 324,200 7.74 22,140 -2.89 n/a n/a n/a
2024-08-14 2024-06-30 13F WESTERN DIGITAL COM Put 300,900 -18.50 22,799 -9.51 n/a n/a n/a
2024-05-13 2024-03-31 13F WESTERN DIGITAL COM Put 369,200 3.97 25,194 35.48 n/a n/a n/a
2024-02-09 2023-12-31 13F WESTERN DIGITAL COM Put 355,100 5.34 18,597 20.90 n/a n/a n/a
2023-11-09 2023-09-30 13F WESTERN DIGITAL COM Put 337,100 39.93 15,382 68.34 n/a n/a n/a
2023-08-11 2023-06-30 13F WESTERN DIGITAL COM Put 240,900 -73.93 9,137 -73.75 n/a n/a n/a
2023-05-12 2023-03-31 13F WESTERN DIGITAL COM Put 924,100 37.95 34,811 64.70 n/a n/a n/a
2023-02-08 2022-12-31 13F WESTERN DIGITAL COM Put 669,900 2.07 21,135 -1.07 n/a n/a n/a
2022-11-10 2022-09-30 13F WESTERN DIGITAL COM Put 656,300 1,351.99 21,363 954.44 n/a n/a n/a
2022-08-10 2022-06-30 13F WESTERN DIGITAL COM Put 45,200 -68.87 2,026 -71.90 n/a n/a n/a
2022-05-16 2022-03-31 13F WESTERN DIGITAL COM Put 145,200 -81.31 7,209 -85.77 n/a n/a n/a
2022-02-14 2021-12-31 13F WESTERN DIGITAL COM Put 776,800 4.97 50,655 21.28 n/a n/a n/a
2021-11-15 2021-09-30 13F WESTERN DIGITAL COM Put 740,000 35.78 41,766 7.68 n/a n/a n/a
2021-08-13 2021-06-30 13F WESTERN DIGITAL COM Put 545,000 142.22 38,788 158.26 n/a n/a n/a
2021-05-12 2021-03-31 13F WESTERN DIGITAL COM Put 225,000 -54.31 15,019 -44.95 n/a n/a n/a
2021-02-11 2020-12-31 13F WESTERN DIGITAL COM Put 492,500 0.00 27,280 51.55 n/a n/a n/a
2020-11-12 2020-09-30 13F WESTERN DIGITAL COM Put 492,500 7.65 18,001 -10.88 n/a n/a n/a
2020-07-31 2020-06-30 13F WESTERN DIGITAL COM Put 457,500 15.09 20,199 22.09 n/a n/a n/a
2020-05-01 2020-03-31 13F WESTERN DIGITAL COM Put 397,500 -47.16 16,544 -65.35 n/a n/a n/a
2020-02-14 2019-12-31 13F WESTERN DIGITAL COM Put 752,300 15.33 47,749 22.74 n/a n/a n/a
2019-11-14 2019-09-30 13F WESTERN DIGITAL COM Put 652,300 -10.92 38,903 11.72 n/a n/a n/a
2019-08-14 2019-06-30 13F WESTERN DIGITAL COM Put 732,300 100.74 34,821 98.61 n/a n/a n/a
2019-05-14 2019-03-31 13F WESTERN DIGITAL COM Put 364,800 37.76 17,532 79.08 n/a n/a n/a
2019-02-14 2018-12-31 13F WESTERN DIGITAL COM Put 264,800 1,051.30 9,790 627.34 n/a n/a n/a
2018-11-14 2018-09-30 13F WESTERN DIGITAL COM Put 23,000 15.00 1,346 -13.05 n/a n/a n/a
2018-08-14 2018-06-30 13F WESTERN DIGITAL COM Put 20,000 -63.64 1,548 -69.50 n/a n/a n/a
2018-05-15 2018-03-31 13F WESTERN DIGITAL COM Put 55,000 -82.26 5,075 -79.42 n/a n/a n/a
2018-02-14 2017-12-31 13F WESTERN DIGITAL COM Put 310,000 31.41 24,654 20.96 n/a n/a n/a
2017-11-14 2017-09-30 13F WESTERN DIGITAL COM Put 235,900 -12.30 20,382 -14.48 n/a n/a n/a
2017-11-14 2017-06-30 13F/A WESTERN DIGITAL COM Put 269,000 398.15 23,833 434.73 n/a n/a n/a
2017-08-14 2017-06-30 13F WESTERN DIGITAL COM Put 269,000 23,833 n/a n/a n/a
2017-11-14 2017-03-31 13F/A WESTERN DIGITAL COM Put 54,000 4,457 n/a n/a n/a
2017-05-12 2017-03-31 13F WESTERN DIGITAL COM Put 54,000 4,457 n/a n/a n/a
2017-02-14 2016-12-31 13F WESTERN DIGITAL COM Put 0 -100.00 0 -100.00 n/a n/a n/a
2016-11-14 2016-09-30 13F WESTERN DIGITAL COM Put 50,900 -94.66 2,976 -93.39 n/a n/a n/a
2016-08-12 2016-06-30 13F WESTERN DIGITAL COM Put 953,100 22.05 45,044 22.10 n/a n/a n/a
2016-05-12 2016-03-31 13F WESTERN DIGITAL COM Put 780,900 83.96 36,890 44.72 n/a n/a n/a
2016-02-16 2015-12-31 13F WESTERN DIGITAL COM Put 424,500 -18.46 25,491 -38.36 n/a n/a n/a
2015-11-13 2015-09-30 13F WESTERN DIGITAL COM Put 520,600 176.77 41,356 180.36 n/a n/a n/a
2015-08-14 2015-06-30 13F WESTERN DIGITAL COM Put 188,100 3,517.31 14,751 3,018.60 n/a n/a n/a
2015-05-14 2015-03-31 13F WESTERN DIGITAL COM Put 5,200 -90.61 473 -92.29 n/a n/a n/a
2015-02-17 2014-12-31 13F WESTERN DIGITAL COM Put 55,400 6,133 n/a n/a n/a
Legend
Shares
The total number of shares held by the institution at the end of the reporting period (the effective date). This is provided in the filing.
Value
The total value of the shares as of the effective date. This is provided in the filing.
Avg. Share Price
The weighted average share price of the shares held by the institution. We use FIFO accounting to determine this price
Class
This is the security class as indicated by the filer. There are a variety of values for this field. Common values include "EC" = equity common, "EP" - equity preferred
Allocation (%)
The percent of the institution's portfolio that this position represents. This is provided in NPORT filings. For 13F filings, we calculate it.
Change in Allocation
The change in allocation from the prior reporting period. This is calculated as current allocation - prior allocation.
Change in Allocation (%)
The percent change in allocation from the prior reporting period. This is calculated as (current allocation - prior allocation) / prior allocation.
Cost Basis
The total cost of the shares held. This is calculated as reported shares * avg. share price
Unrealized Gain/Loss
This is the market value of the position as of the effective date minus the cost basis.