Supplemental Information June 4, 2026 Exhibit 99.1

Q1 2026 2 Table of Contents PORTFOLIO INFORMATION Summary Same Property Results................................................................................................................................................ 4 Occupancy and Leasing Summary............................................................................................................................................. 5 Tenant Diversity and Credit Characteristics ............................................................................................................................. 6 Tenants Representing 1% or More of Total Annualized Rental Income ............................................................................. 7 Lease Expiration Schedule........................................................................................................................................................... 8 Capital Expenditures Summary .................................................................................................................................................. 9 Property Dispositions.................................................................................................................................................................... 10 Investment in Unconsolidated Joint Venture........................................................................................................................... 11 APPENDIX Calculation and Reconciliation of NOI and Cash Basis NOI.................................................................................................. 13 Reconciliation and Calculation of Same Property NOI and Same Property Cash Basis NOI.......................................... 14 Property Details (by Collateral Pool).......................................................................................................................................... 15 Non-GAAP Financial Measures and Certain Definitions........................................................................................................ 22 WARNING CONCERNING FORWARD-LOOKING STATEMENTS....................................................................................................... 23 Corporate Headquarters: Two Newton Place 255 Washington Street, Suite 300 Newton, Massachusetts 02458-1634 www.opireit.com Investor Relations Contact: Kevin Barry, Senior Director (617) 219-1410 [email protected] [email protected] All amounts in this presentation are unaudited. Unless otherwise noted, all data presented in this presentation excludes two properties, which are encumbered by a $48.9 million mortgage note, owned by an unconsolidated joint venture in which OPI owns a 51% interest. See page 11 for information regarding this joint venture and its related mortgage note. Please refer to Non-GAAP Financial Measures and Certain Definitions for terms used throughout this presentation.

RETURN TO TABLE OF CONTENTS Q1 2026 3 Portfolio Information

RETURN TO TABLE OF CONTENTS Q1 2026 4 For the Three Months Ended 3/31/2026 3/31/2025 Properties (end of period) 117 117 Rentable sq. ft. 16,350 16,355 Percent leased 81.3% 85.4% Rental income $ 99,742 $ 103,899 Same Property NOI $ 55,398 $ 60,482 Same Property Cash Basis NOI $ 52,646 $ 52,904 Same Property NOI % margin 55.5% 58.2% Same Property Cash Basis NOI % margin 54.2% 54.9% Same Property NOI % change (8.4%) Same Property Cash Basis NOI % change (0.5%) Summary Same Property Results (dollars and sq. ft. in thousands) Houston, TX

RETURN TO TABLE OF CONTENTS Q1 2026 5 As of and for the Three Months Ended 3/31/2026 12/31/2025 9/30/2025 6/30/2025 3/31/2025 Properties (end of period) 122 122 124 125 125 Rentable sq. ft. 17,113 17,113 17,214 17,270 17,274 Percentage leased 78.2% 78.2% 78.3% 81.2% 81.3% Leasing Activity (Sq. Ft.): New leases 35 49 51 138 50 Renewals 177 104 131 278 173 Total 212 153 182 416 223 % Change in GAAP Rent: (1) New leases 12.1% (15.9%) (26.7%) 8.5% (3.5%) Renewals 8.8% (19.7%) (11.6%) 5.2% 19.3% Total 9.3% (18.6%) (16.7%) 6.4% 13.5% Weighted Average Lease Term by Sq. Ft. (years): New leases 1.6 7.5 4.7 4.7 10.3 Renewals 5.1 7.9 4.2 5.8 10.3 Total 4.5 7.8 4.3 5.4 10.3 Leasing Cost and Concession Commitments: New leases $ 513 $ 1,084 $ 1,217 $ 6,050 $ 3,788 Renewals 4,003 5,664 1,292 1,924 6,835 Total $ 4,516 $ 6,748 $ 2,509 $ 7,974 $ 10,623 Leasing Cost and Concession Commitments per Sq. Ft.: New leases $ 14.73 $ 21.75 $ 23.90 $ 44.00 $ 75.50 Renewals $ 22.67 $ 54.88 $ 9.81 $ 6.93 $ 39.47 Total $ 21.36 $ 44.09 $ 13.74 $ 19.21 $ 47.56 Leasing Cost and Concession Commitments per Sq. Ft. per Year: New leases $ 9.24 $ 2.88 $ 5.10 $ 9.34 $ 7.33 Renewals $ 4.48 $ 6.91 $ 2.33 $ 1.20 $ 3.83 Total $ 4.76 $ 5.64 $ 3.16 $ 3.53 $ 4.62 (1) Percent difference in prior rents charged for same space or, in the case of space acquired vacant, market rental rates for similar space in the building at the date of acquisition. Rents include estimated recurring expense reimbursements paid to us, exclude lease value amortization and are net of lease concessions. Occupancy and Leasing Summary (dollars and sq. ft. in thousands, except per sq. ft. data) This leasing summary is based on leases entered during the periods indicated.

RETURN TO TABLE OF CONTENTS Q1 2026 6 Investment Grade 60.1% Not Rated 33.0% Non-Investment Grade 6.9% Percentage of Total Annualized Rental Income Tenant Credit Characteristics ( 4 ) (3) Tenant Industry Tenant Diversity and Credit Characteristics As of March 31, 2026 U.S. Government: 17.5% Technology & Communications: 15.3% Real Estate & Legal & Other Financial: 14.9% Professional Services: 13.6% Manufacturing & Transportation: 13.5% Government Contractors: 8.9% State and Municipalities: 8.6% Other: 4.5% Life Sciences and Medical: 3.2%

RETURN TO TABLE OF CONTENTS Q1 2026 7 Tenant Credit Rating Sq. Ft. % of Leased Sq. Ft. Annualized Rental Income % of Total Annualized Rental Income 1 U.S. Government Investment Grade 2,415 18.1% $ 67,840 17.5% 2 Alphabet Inc. (Google) Investment Grade 386 2.9% 21,753 5.6% 3 IG Investments Holdings LLC Not Rated 337 2.5% 18,659 4.8% 4 Bank of America Corporation Investment Grade 577 4.3% 17,076 4.4% 5 Shook, Hardy & Bacon L.L.P. Not Rated 412 3.1% 13,638 3.5% 6 Northrop Grumman Corporation Investment Grade 337 2.5% 10,706 2.8% 7 State of California Investment Grade 367 2.7% 10,330 2.7% 8 State of Georgia Investment Grade 308 2.3% 8,135 2.1% 9 Sonoma Biotherapeutics, Inc. Not Rated 84 0.6% 7,492 1.9% 10 Genesys Cloud Services Holdings I, LLC Non Investment Grade 275 2.1% 6,297 1.6% 11 Automatic Data Processing, Inc. Investment Grade 289 2.2% 6,285 1.6% 12 Compass Group plc Investment Grade 267 2.0% 6,122 1.6% 13 Church & Dwight Co., Inc. Investment Grade 250 1.9% 6,055 1.6% 14 Leidos Holdings Inc. Investment Grade 159 1.2% 5,823 1.5% 15 AT&T Inc. Investment Grade 425 3.2% 5,751 1.5% 16 Primerica, Inc. Investment Grade 344 2.6% 5,730 1.5% 17 Science Applications International Corp Non Investment Grade 159 1.2% 5,118 1.3% 18 Rocky Mountain University of Health Professions, Inc. Not Rated 170 1.3% 4,523 1.2% 19 CommScope Holding Company Inc. Non Investment Grade 96 0.7% 4,507 1.2% 20 Hartford Financial Services Group Inc Investment Grade 143 1.1% 4,424 1.1% 21 Berkshire Hathaway Inc. Investment Grade 134 1.0% 4,255 1.1% 22 BAE Systems plc Investment Grade 139 1.0% 3,920 1.0% 8,073 60.5% $ 244,439 63.1% Tenants Representing 1% or More of Total Annualized Rental Income As of March 31, 2026 (dollars and sq. ft. in thousands)

RETURN TO TABLE OF CONTENTS Q1 2026 8 Year (1) Number of Leases Expiring Leased Square Feet Expiring % of Total Leased Square Feet Expiring Cumulative % of Total Leased Square Feet Expiring Annualized Rental Income Expiring % of Total Annualized Rental Income Expiring Cumulative % of Total Annualized Rental Income Expiring 2026 33 369 2.8% 2.8% $ 12,202 3.1% 3.1% 2027 35 1,818 13.6% 16.4% 48,454 12.5% 15.6% 2028 18 512 3.8% 20.2% 27,103 7.0% 22.6% 2029 39 1,091 8.2% 28.4% 33,068 8.5% 31.1% 2030 31 1,060 7.9% 36.3% 32,126 8.3% 39.4% 2031 29 1,629 12.2% 48.5% 38,670 10.0% 49.4% 2032 16 605 4.5% 53.0% 18,546 4.8% 54.2% 2033 15 1,258 9.4% 62.4% 24,775 6.4% 60.6% 2034 12 1,789 13.4% 75.8% 48,971 12.6% 73.2% 2035 and thereafter 34 3,244 24.2% 100.0% 104,383 26.8% 100.0% Total 262 13,375 100.0% $ 388,298 100.0% Weighted average remaining lease term (in years) 6.4 6.4 (1) The year of lease expiration is pursuant to current contract terms. Lease Expiration Schedule As of March 31, 2026 (dollars and sq. ft. in thousands) Atlanta, GA

RETURN TO TABLE OF CONTENTS Q1 2026 9 For the Three Months Ended 3/31/2026 12/31/2025 9/30/2025 6/30/2025 3/31/2025 Lease related costs $ 8,458 $ 15,624 $ 4,257 $ 8,830 $ 10,727 Building improvements 2,350 2,292 3,922 4,327 3,011 Recurring capital expenditures 10,808 17,916 8,179 13,157 13,738 Development, redevelopment and other activities 109 (262) 598 565 83 Total capital expenditures $ 10,917 $ 17,654 $ 8,777 $ 13,722 $ 13,821 Average rentable sq. ft. during period 17,113 17,164 17,242 17,272 17,519 Building improvements per average sq. ft. during period $ 0.14 $ 0.13 $ 0.23 $ 0.25 $ 0.17 Capital Expenditures Summary (dollars and sq. ft. in thousands, except per sq. ft. data) Capital Expenditures Summary San Jose, CA

RETURN TO TABLE OF CONTENTS Q1 2026 10 Dispositions: Date Sold Location Number of Properties Sq. Ft. Gross Sales Price Gross Sales Price Per Sq. Ft. 7/8/2025 Detroit, MI 1 56 $ 2,150 $ 38.39 12/19/2025 Tempe, AZ 2 101 11,038 109.29 Total 3 157 $ 13,188 $ 84.00 Property Dispositions Since July 1, 2025 (dollars and sq. ft. in thousands, except per sq. ft. data)

RETURN TO TABLE OF CONTENTS Q1 2026 11 Unconsolidated Joint Venture: Joint Venture OPI Ownership OPI Investment Number of Properties Location Sq. Ft. Occupancy Weighted Average Remaining Lease Term (1) Prosperity Metro Plaza 51% $ 17,075 2 Fairfax, VA 346 89.8% 4.6 years (1) Lease term is weighted based on annualized rental income. (2) Includes the effect of mark to market accounting. (3) Reflects OPI's proportionate share of the principal debt balance based on its ownership percentage of the joint venture; none of the debt is recourse to OPI. (4) Reflects OPI's proportionate share of operating results based on its ownership percentage of the joint venture. (5) Includes interest expense, net of other income. (6) OPI's unconsolidated joint venture reports rental income on a straight line basis over the terms of the respective leases; accordingly, rental income includes non-cash straight line rent adjustments. Rental income also includes expense reimbursements, tax escalations, parking revenues, service income and other fixed and variable charges paid to the unconsolidated joint venture by its tenants, as well as the net effect of non-cash amortization of intangible lease assets and liabilities. Investment in Unconsolidated Joint Venture As of March 31, 2026 (dollars and sq. ft. in thousands) Results of Operations - Prosperity Metro Plaza: (4) For the Three Months Ended March 31, 2026 Equity in losses $ 110 Depreciation and amortization 582 Other expenses, net (5) 236 NOI 928 Non-cash straight line rent adjustments included in rental income (6) (86) Cash Basis NOI $ 842 Outstanding Unconsolidated Debt: Joint Venture OPI Ownership Interest Rate (2) Maturity Date Principal Balance Annual Debt Service Principal Balance at Maturity OPI Share of Principal Balance (3) Prosperity Metro Plaza 51% 4.090% 12/1/2029 $ 48,877 $ 2,833 $ 45,246 $ 24,927

RETURN TO TABLE OF CONTENTS Q1 2026 12 Appendix

RETURN TO TABLE OF CONTENTS Q1 2026 13 For the Three Months Ended 3/31/2026 12/31/2025 9/30/2025 6/30/2025 3/31/2025 Calculation of NOI and Cash Basis NOI: Rental income $ 108,868 $ 105,315 $ 109,127 $ 114,499 $ 113,615 Property operating expenses (52,455) (43,980) (52,105) (49,031) (52,230) NOI 56,413 61,335 57,022 65,468 61,385 Non-cash straight line rent adjustments included in rental income (1,936) (4,832) (4,750) (6,636) (6,856) Lease value amortization included in rental income (140) (140) (140) (159) (123) Lease termination fees included in rental income (655) (817) (1,179) (582) (559) Non-cash amortization included in other operating expenses (13) (13) (13) (13) (13) Cash Basis NOI $ 53,669 $ 55,533 $ 50,940 $ 58,078 $ 53,834 Reconciliation of Net (Loss) Income to NOI and Cash Basis NOI: Net loss $ (93,021) $ (118,982) $ (66,339) $ (41,186) $ (45,867) Equity in net (losses) earnings of investees (110) (90) 115 128 252 Income tax (benefit) expense (146) 146 (261) 94 137 Loss before income tax (benefit) expense and equity in net (losses) earnings of investees (93,277) (118,926) (66,485) (40,964) (45,478) Reorganization items, net 59,532 78,333 — — — Net loss (gain) on early extinguishment of debt — — 354 (148) 243 Interest expense 42,207 44,310 53,259 52,507 53,378 Interest and other income (431) (394) (802) (788) (1,162) Loss (gain) on sale of real estate — (5,488) (6) (159) 4,737 General and administrative 4,299 4,591 4,964 4,816 5,058 Transaction related costs — 14,735 22,904 3,940 876 Loss (gain) on impairment of real estate — (378) — 2,426 — Depreciation and amortization 44,083 44,552 42,834 43,838 43,733 NOI 56,413 61,335 57,022 65,468 61,385 Non-cash amortization included in other operating expenses (13) (13) (13) (13) (13) Lease termination fees included in rental income (655) (817) (1,179) (582) (559) Lease value amortization included in rental income (140) (140) (140) (159) (123) Non-cash straight line rent adjustments included in rental income (1,936) (4,832) (4,750) (6,636) (6,856) Cash Basis NOI $ 53,669 $ 55,533 $ 50,940 $ 58,078 $ 53,834 Calculation and Reconciliation of NOI and Cash Basis NOI (dollars in thousands)

RETURN TO TABLE OF CONTENTS Q1 2026 14 For the Three Months Ended 3/31/2026 3/31/2025 Reconciliation of NOI to Same Property NOI: Rental income $ 108,868 $ 113,615 Property operating expenses (52,455) (52,230) NOI 56,413 61,385 Less: NOI of properties not included in same property results (1,015) (903) Same Property NOI $ 55,398 $ 60,482 Calculation of Same Property Cash Basis NOI: Same Property NOI $ 55,398 $ 60,482 Add: Lease value amortization included in rental income (140) (170) Less: Non-cash straight line rent adjustments included in rental income (1,852) (6,745) Lease termination fees included in rental income (655) (559) Non-cash amortization included in property operating expenses (105) (104) Same Property Cash Basis NOI $ 52,646 $ 52,904 Reconciliation and Calculation of Same Property NOI and Same Property Cash Basis NOI (dollars in thousands) Seattle, WA

RETURN TO TABLE OF CONTENTS Q1 2026 15 Property Detail (by Collateral Pool) As of March 31, 2026 (dollars and sq. ft. in thousands) Number of Properties Sq. Ft. Sq. Ft. Expiring Through December 31st, 2026 Occupancy Weighted Average Remaining Lease Term Annualized Rental Income Trailing Twelve Months NOI Trailing Twelve Months Cash Basis NOI Unspent Leasing Related Obligations Gross Book Value of Real Estate Assets Encumbered Properties (1) Credit Agreement 2235 Iron Point Road, Folsom, CA 1 96 — 100.0% 3.6 $ 2,895 $ 2,311 $ 2,449 $ — $ 14,138 4560 Viewridge Avenue, San Diego, CA 1 93 — 100.0% 5.2 3,524 2,326 2,380 — 28,961 440 First Street, NW, Washington, D.C. 1 142 22 82.9% 6.1 7,942 4,442 3,870 17 94,276 180 Ted Turner Drive SW, Atlanta, GA 1 91 — 100.0% 11.4 3,695 2,132 1,256 — 37,640 600 West Peachtree Street NW, Atlanta, GA 1 387 3 94.8% 3.6 9,820 5,730 6,243 323 71,440 1000 West Fulton Market, Chicago, IL 1 545 — 92.9% 3.2 27,939 15,420 14,912 — 364,228 2020 S. Arlington Heights, Arlington Heights, IL 1 58 — 100.0% 14.8 1,682 1,040 1,132 — 18,784 2555 Grand Boulevard, Kansas City, MO 1 596 — 69.2% 7.9 13,638 7,408 6,816 7,417 98,394 2300 Yorkmont Road, Charlotte, NC 1 151 17 100.0% 4.2 3,498 2,136 2,297 — 26,267 2400 Yorkmont Road, Charlotte, NC 1 133 — 100.0% 4.8 3,054 1,702 1,844 — 15,939 14668 Lee Road, Chantilly, VA 1 170 — 97.5% 13.1 5,847 4,134 3,836 — 58,223 14672 Lee Road, Chantilly, VA 1 159 — 100.0% 1.1 5,118 3,674 3,883 — 47,828 1751 Blue Hills Drive, Roanoke, VA 1 399 — 100.0% 7.5 2,168 1,768 1,800 — 15,431 45101 Warp Drive, Sterling, VA 1 161 — 100.0% 8.4 5,114 3,394 3,476 — 33,670 45201 Warp Drive, Sterling, VA 1 88 — 100.0% 8.4 2,806 1,840 1,887 — 18,748 45301 Warp Drive, Sterling, VA 1 88 — 100.0% 8.4 2,786 1,841 1,883 401 50,817 2420 Stevens Center Place, Richland, WA 1 93 — 100.0% 7.5 2,565 1,636 1,403 — 16,699 2430 Stevens Center Place, Richland, WA 1 47 — 100.0% 7.5 1,304 771 653 — 9,222 5353 Yellowstone Road, Cheyenne, WY 1 106 — 92.9% 14.7 2,590 1,745 1,104 75 15,066 Credit Agreement 19 3,603 42 92.3% 6.1 107,985 65,450 63,124 8,233 1,035,771 (1) For more information on OPI's debt agreements and encumbrances, see OPI's Quarterly Report on Form 10-Q for the quarter ended March 31, 2026 which is available on the SEC's website at www.sec.gov.

RETURN TO TABLE OF CONTENTS Q1 2026 16 Property Detail (by Collateral Pool) As of March 31, 2026 (dollars and sq. ft. in thousands) Number of Properties Sq. Ft. Sq. Ft. Expiring Through December 31st, 2026 Occupancy Weighted Average Remaining Lease Term Annualized Rental Income Trailing Twelve Months NOI Trailing Twelve Months Cash Basis NOI Unspent Leasing Related Obligations Gross Book Value of Real Estate Assets $445M Senior Notes due 2027 2115 O'Nel Drive, San Jose, CA 1 99 — 100.0% 7.7 2,908 2,482 3,029 1,483 24,357 2544 Campbell Place, Carlsbad, CA 1 45 — 100.0% 6.3 1,259 650 155 1,109 6,911 47131 Bayside Parkway, Fremont, CA 1 101 — 100.0% 11.8 3,230 2,548 23 — 18,407 11 Dupont Circle, NW, Washington, D.C. 1 159 — 74.7% 6.2 7,198 4,638 3,212 103 110,259 1401 K Street, NW, Washington, D.C. 1 130 8 57.7% 4.5 3,981 1,231 1,394 — 84,974 20 Massachusetts Avenue NW, Washington, D.C. (1) 1 188 — —% — — 2,238 2,636 — 283,916 625 Indiana Avenue, NW, Washington, D.C. 1 165 60 94.7% 5.5 7,724 4,386 4,249 — 64,310 8900 Grand Oak Circle, Tampa, FL 1 68 — 100.0% 5.9 2,066 1,103 1,108 — 15,550 100 North Washington Street, Boston, MA 1 49 8 33.7% 1.3 641 14 37 121 27,606 126-132 North Washington Street, Boston, MA 1 13 8 100.0% 0.6 396 55 55 — 11,865 25 Newport Avenue Extension, Quincy, MA 1 93 1 100.0% 5.2 2,480 1,143 1,098 — 16,988 251 Causeway Street, Boston, MA 1 141 — —% — — (1,502) (1,516) — 30,850 10320 Little Patuxent Parkway, Columbia, MD 1 155 2 47.6% 3.4 2,331 590 665 139 31,978 2009-2011 Commerce Park Drive, Annapolis, MD 1 51 — 100.0% 11.1 1,822 1,209 1,083 — 11,622 4201 Patterson Avenue, Baltimore, MD 1 85 85 100.0% — 1,270 703 694 — 12,121 520 Gaither Road, Rockville, MD 1 139 — 100.0% 5.9 3,920 2,194 2,481 4,604 46,252 530 Gaither Road, Rockville, MD 1 216 98 100.0% 2.5 6,991 4,028 3,282 340 60,762 534 Gaither Road, Rockville, MD 1 3 — 100.0% 10.7 23 (21) (21) — 608 540 Gaither Road, Rockville, MD 1 131 — 61.2% 3.3 2,409 831 1,218 — 35,194 (1) Sq. Ft. excludes 240 square feet under a hotel management agreement.

RETURN TO TABLE OF CONTENTS Q1 2026 17 Property Detail (by Collateral Pool) As of March 31, 2026 (dollars and sq. ft. in thousands) Number of Properties Sq. Ft. Sq. Ft. Expiring Through December 31st, 2026 Occupancy Weighted Average Remaining Lease Term Annualized Rental Income Trailing Twelve Months NOI Trailing Twelve Months Cash Basis NOI Unspent Leasing Related Obligations Gross Book Value of Real Estate Assets $445M Senior Notes due 2027 - Continued 6315 Hillside Court, Columbia, MD 1 44 — 19.6% 2.2 178 (38) (27) — 6,009 7001 Columbia Gateway Drive, Columbia, MD 1 117 — 69.5% 4.3 2,493 1,061 1,098 957 31,670 4241 NE 34th Street, Kansas City, MO 1 88 — 100.0% 4.5 2,048 839 830 — 12,112 299 Jefferson Road, Parsippany, NJ 1 151 — —% — — (854) (854) — 20,497 10b Airline Drive, Colonie, NY 1 64 — 100.0% 4.9 917 552 594 34 10,879 1212 Pittsford - Victor Road, Pittsford, NY 1 55 — 100.0% 3.8 1,169 536 525 — 4,573 8800 Tinicum Boulevard, Philadelphia, PA 1 441 — —% — — (2,721) (2,721) — 55,430 446 Wrenplace Road, Fort Mill, SC 1 150 — 100.0% 5.5 2,962 2,731 2,677 — 35,388 1511 East Common Street, New Braunfels, TX 1 63 — 100.0% 4.3 2,017 980 946 100 10,499 8675,8701-8711 Freeport Pkwy and 8901 Esters Blvd, Irving, TX 3 458 — —% — — (277) (190) — 64,483 45600 Woodland Road, Sterling, VA 1 110 — 100.0% 4.0 3,627 2,492 2,460 449 26,602 45610 Woodland Road, Sterling, VA 1 111 6 78.5% 5.3 2,529 1,184 932 284 27,996 7987 Ashton Avenue, Manassas, VA 1 69 — 100.0% 4.8 1,694 973 1,098 1,007 13,708 9960 Mayland Drive, Richmond, VA 1 174 — 99.0% 0.8 3,609 2,266 2,596 — 27,822 $445M Senior Notes due 2027 35 4,126 276 57.8% 5.0 73,892 38,244 34,846 10,730 1,242,198

RETURN TO TABLE OF CONTENTS Q1 2026 18 Property Detail (by Collateral Pool) As of March 31, 2026 (dollars and sq. ft. in thousands) Number of Properties Sq. Ft. Sq. Ft. Expiring Through December 31st, 2026 Occupancy Weighted Average Remaining Lease Term Annualized Rental Income Trailing Twelve Months NOI Trailing Twelve Months Cash Basis NOI Unspent Leasing Related Obligations Gross Book Value of Real Estate Assets $300M Senior Notes due 2029 15451 North 28th Avenue, Phoenix, AZ 1 67 — 100.0% 6.8 1,444 867 681 — 14,733 2500 Walsh Avenue, Santa Clara, CA 1 66 — 100.0% 8.8 2,872 2,169 2,013 — 23,197 2548 Campbell Place, Carlsbad, CA 1 46 — 100.0% 5.0 1,831 1,529 1,583 — 11,232 350 West Java Drive, Sunnyvale, CA 1 96 — 100.0% 6.7 4,507 3,582 3,629 — 32,904 77 Rio Robles Drive, San Jose, CA 1 68 — 100.0% 4.7 2,660 1,801 1,913 — 25,818 915 L Street, Sacramento, CA 1 164 4 98.0% 4.7 5,716 3,652 3,678 — 50,489 9815 Goethe Road, Sacramento, CA 1 88 — 100.0% 7.3 2,096 1,171 1,145 8 19,413 7850 Southwest 6th Court, Plantation, FL 1 136 — 100.0% 11.6 4,255 2,831 2,649 — 58,676 1224 Hammond Drive NE, Atlanta, GA 1 358 — 97.4% 9.6 18,659 12,606 12,073 54 191,091 1185 South Vinnell Way, Boise, ID 1 30 — 100.0% 15.9 1,031 511 447 — 10,726 1249 South Vinnell Way, Boise, ID 1 60 — 100.0% 5.6 1,415 757 742 860 12,883 1387 South Vinnell Way, Boise, ID 1 91 — 100.0% 5.6 2,034 1,147 1,098 1,309 18,525 12515-4 Research Boulevard, Austin, TX 1 93 — 100.0% 3.3 2,878 1,941 2,093 — 15,589 3600 Wiseman Boulevard, San Antonio, TX 1 100 — 100.0% 6.6 3,288 2,055 2,016 — 20,902 1800 Novell Place, Provo, UT 1 412 — 87.8% 9.7 9,381 6,037 4,929 119 97,524 2101 Bermuda Hundred Drive, Chester, VA 1 225 — 100.0% 7.8 1,414 1,119 1,069 — 14,061 65 Bowdoin Street, S. Burlington, VT 1 27 — 100.0% 3.3 1,178 668 665 — 10,122 $300M Senior Notes due 2029 17 2,127 4 96.9% 8.0 66,659 44,443 42,423 2,350 627,885

RETURN TO TABLE OF CONTENTS Q1 2026 19 Property Detail (by Collateral Pool) As of March 31, 2026 (dollars and sq. ft. in thousands) Number of Properties Sq. Ft. Sq. Ft. Expiring Through December 31st, 2026 Occupancy Weighted Average Remaining Lease Term Annualized Rental Income Trailing Twelve Months NOI Trailing Twelve Months Cash Basis NOI Unspent Leasing Related Obligations Gross Book Value of Real Estate Assets $610M Senior Notes due 2029 445 Jan Davis Drive, Huntsville, AL 1 57 — 100.0% 5.3 948 846 853 — 6,840 10350 NW 112th Avenue, Miami, FL 1 79 — 100.0% 1.8 3,337 2,449 2,449 — 19,145 4712 Southpark Boulevard, Ellenwood, GA 1 352 — 100.0% 8.4 4,046 2,569 1,695 3,237 25,439 1415 West Diehl Road, Naperville, IL 1 735 — 55.5% 6.0 10,695 6,536 5,842 — 121,866 330 Billerica Road, Chelmsford, MA 1 98 5 59.1% 9.3 1,479 822 741 — 12,739 2645 and 2655 Long Lake Road, Roseville, MN 1 58 — 100.0% 9.2 1,312 646 481 — 11,327 18010 Burt Street, Omaha, NE 1 101 — 100.0% 8.3 2,369 1,824 1,344 — 19,453 2231 Schrock Road, Columbus, OH 1 42 — 100.0% 6.3 517 420 394 — 3,661 10451 Clay Road, Houston, TX 1 97 — 100.0% 3.0 2,312 2,193 1,893 — 23,673 16001 North Dallas Parkway, Addison, TX 2 554 — 100.0% 10.9 16,387 11,210 2,381 17,475 122,098 202 North Castlegory Road, Houston, TX 1 84 — 100.0% 1.8 2,826 1,654 1,697 — 14,396 3400 West Plano Parkway, Plano, TX 1 235 — 100.0% 5.1 1,710 1,776 1,517 — 25,711 4221 W. John Carpenter Freeway, Irving, TX 1 54 — 100.0% 7.2 936 696 633 790 6,189 14660 Lee Road, Chantilly, VA 1 80 — 100.0% 3.8 2,908 1,997 1,740 — 25,650 Two Commercial Place, Norfolk, VA 1 289 — 100.0% 1.3 6,285 4,064 4,352 — 41,858 351 Elliott Ave West, Seattle, WA 1 108 — —% — — (1,153) (1,153) — 41,005 401 Elliott Ave West, Seattle, WA 1 77 — 1.9% 2.9 86 (1,261) (1,260) — 103,574 501 Elliott Ave West, Seattle, WA 1 114 — 73.3% 8.5 7,492 5,738 5,358 — 110,784 $610M Senior Notes due 2029 19 3,214 5 81.9% 6.8 65,645 43,026 30,957 21,502 735,408

RETURN TO TABLE OF CONTENTS Q1 2026 20 Property Detail (by Collateral Pool) As of March 31, 2026 (dollars and sq. ft. in thousands) Number of Properties Sq. Ft. Sq. Ft. Expiring Through December 31st, 2026 Occupancy Weighted Average Remaining Lease Term Annualized Rental Income Trailing Twelve Months NOI Trailing Twelve Months Cash Basis NOI Unspent Leasing Related Obligations Gross Book Value of Real Estate Assets Mortgage Notes 145 Rio Robles Drive, San Jose, CA 1 58 — 100.0% 7.3 2,229 1,604 1,556 — 21,283 One Primerica Parkway, Duluth, GA 1 344 — 100.0% 9.8 5,730 5,340 5,198 7,614 55,994 3300 75th Avenue, Landover, MD 1 266 — 100.0% 13.4 4,837 4,476 4,379 — 48,328 1220 Echelon Parkway, Jackson, MS 1 110 — 100.0% 18.6 4,180 2,236 975 550 33,754 500 Charles Ewing Boulevard, Ewing, NJ 1 250 — 100.0% 7.2 6,055 5,676 5,791 — 53,505 701 Clay Road, Waco, TX 1 139 — 100.0% 9.8 3,161 1,704 1,925 — 25,827 22330 Glenn Drive, Sterling, VA 1 167 — 100.0% 5.4 5,488 3,872 3,763 1,683 67,247 Mortgage Notes 7 1,334 — 100.0% 10.1 31,680 24,908 23,587 9,847 305,938 Other Properties Collateralized in Debtor-in- Possession Financing 131 Clayton Street, Montgomery, AL 1 58 — 100.0% 1.3 1,786 1,111 1,105 — 12,229 4344 Carmichael Road, Montgomery, AL 1 49 — 100.0% 3.1 1,631 1,185 1,056 — 16,750 711 S 14th Avenue, Safford, AZ 1 36 2 100.0% 3.1 1,069 642 635 — 9,273 100 Redwood Shores Parkway, Redwood City, CA 1 63 — 23.5% 2.9 582 2,381 2,286 — 28,849 10949 N. Mather Boulevard, Rancho Cordova, CA 1 94 — 100.0% 1.3 2,609 1,540 1,679 — 22,770 11020 Sun Center Drive, Rancho Cordova, CA 1 83 — 100.0% 10.8 2,024 1,108 1,007 — 19,167 51 Rio Robles Drive, San Jose, CA 1 61 — 100.0% 1.3 2,352 2,069 2,049 — 15,119 603 San Juan Avenue, Stockton, CA 1 22 — 100.0% 1.0 971 479 642 — 8,729 12795 West Alameda Parkway, Lakewood, CO 1 167 — —% — — (836) (853) — 5,831 7958 South Chester Street, Centennial, CO 1 167 — 47.7% 7.4 1,865 (640) (982) — 26,547

RETURN TO TABLE OF CONTENTS Q1 2026 21 Property Detail (by Collateral Pool) As of March 31, 2026 (dollars and sq. ft. in thousands) Number of Properties Sq. Ft. Sq. Ft. Expiring Through December 31st, 2026 Occupancy Weighted Average Remaining Lease Term Annualized Rental Income Trailing Twelve Months NOI Trailing Twelve Months Cash Basis NOI Unspent Leasing Related Obligations Gross Book Value of Real Estate Assets Other Properties Collateralized in Debtor-in- Possession Financing - Continued 1211 Connecticut Avenue, NW, Washington, D.C. 1 140 10 38.0% 6.5 2,390 1,289 506 120 68,893 840 First Street, NE, Washington, D.C. 1 253 — 15.4% 4.5 2,060 405 642 — 148,339 8305 NW 62nd Avenue, Johnston, IA 1 199 — 100.0% 0.8 3,283 2,685 3,165 — 26,861 7601 Interactive Way, Indianapolis, IN 1 120 — 100.0% 1.3 2,791 1,751 1,845 60 16,912 7635 Interactive Way, Indianapolis, IN 1 155 — 100.0% 1.3 3,506 2,227 2,349 76 19,824 2001-2003 Commerce Park Drive, Annapolis, MD 1 52 5 50.1% 4.2 544 326 327 — 9,326 6310 Hillside Court, Columbia, MD 1 43 6 100.0% 3.3 1,170 695 726 — 5,687 3550 Green Court, Ann Arbor, MI 1 82 — 100.0% 1.6 1,721 1,614 1,693 — 13,392 18020 Burt Street, Omaha, NE 1 101 — 44.7% 10.3 1,186 (58) (813) — 16,817 9680 Old Bailes Road, Fort Mill, SC 1 60 — 100.0% 1.7 825 692 711 — 6,542 12515-3 Research Boulevard, Austin, TX 1 55 — —% — — (472) (472) — 9,311 2900 West Plano Parkway, Plano, TX 1 191 — 100.0% 5.1 4,040 1,992 1,727 1 25,305 1760 Business Center Drive, Reston, VA 1 275 — —% — — (666) (694) — 80,851 1775 Wiehle Avenue, Reston, VA 1 135 19 60.0% 5.6 2,663 1,509 1,694 1,471 42,443 9201 Forest Hill Avenue, Richmond, VA 1 48 — 100.0% 1.8 1,369 756 872 — 4,925 Vacant land parcels and other — — — —% — — (66) (68) — 6,055 Other Properties Collateralized Debtor-in- Possession Financing 25 2,709 47 60.5% 3.5 42,437 23,718 22,834 1,728 666,747 Sold Properties — — — —% — — 449 449 — — Total / Weighted Average 122 17,113 369 78.2% 6.4 $ 388,298 $ 240,238 $ 218,220 $ 54,390 $ 4,613,947

RETURN TO TABLE OF CONTENTS Q1 2026 22 Non-GAAP Financial Measures OPI presents certain “non-GAAP financial measures” within the meaning of the applicable rules of the Securities and Exchange Commission, or the SEC, including NOI, Cash Basis NOI, Same Property NOI and Same Property Cash Basis NOI. These measures do not represent cash generated by operating activities in accordance with GAAP and should not be considered alternatives to net income (loss) as indicators of OPI's operating performance or as measures of OPI's liquidity. These measures should be considered in conjunction with net income (loss) as presented in OPI's consolidated statements of income (loss). OPI considers these non-GAAP measures to be appropriate supplemental measures of operating performance for a REIT, along with net income (loss). OPI believes these measures provide useful information to investors because by excluding the effects of certain historical amounts, such as depreciation and amortization expense, they may facilitate a comparison of OPI's operating performance between periods and with other REITs and, in the case of NOI, Cash Basis NOI, Same Property NOI and Same Property Cash Basis NOI reflecting only those income and expense items that are generated and incurred at the property level may help both investors and management to understand the operations of OPI's properties. NOI and Cash Basis NOI The calculations of net operating income, or NOI, and Cash Basis NOI exclude certain components of net income (loss) in order to provide results that are more closely related to OPI's property level results of operations. OPI calculates NOI and Cash Basis NOI as shown on page 12 and Same Property NOI and Same Property Cash Basis NOI as shown on page 13. OPI defines NOI as income from OPI's real estate less OPI's property operating expenses. NOI excludes amortization of capitalized tenant improvement costs and leasing commissions that OPI records as depreciation and amortization expense. OPI defines Cash Basis NOI as NOI excluding non-cash straight line rent adjustments, lease value amortization, lease termination fees, if any, and non-cash amortization included in other operating expenses. OPI calculates Same Property NOI and Same Property Cash Basis NOI in the same manner that OPI calculates the corresponding NOI and Cash Basis NOI amounts, except that OPI only includes same properties in calculating Same Property NOI and Same Property Cash Basis NOI. OPI uses NOI, Cash Basis NOI, Same Property NOI and Same Property Cash Basis NOI to evaluate individual and company-wide property level performance. Other real estate companies and REITs may calculate NOI, Cash Basis NOI, Same Property NOI and Same Property Cash Basis NOI differently than OPI does. Annualized rental income is calculated using the annualized contractual base rents from OPI's tenants pursuant to its lease agreements as of March 31, 2026, plus straight line rent adjustments and estimated recurring expense reimbursements to be paid to OPI, and excluding lease value amortization. Building improvements generally include expenditures to replace obsolete building components and expenditures that extend the useful life of existing assets. Development, redevelopment and other activities generally include capital expenditure projects that reposition a property or result in new sources of revenue. GAAP is U.S. generally accepted accounting principles. Gross book value of real estate assets is real estate properties at cost calculated in accordance with GAAP, plus certain acquisition costs, if any, before depreciation and purchase price allocations, less impairment writedowns, if any. Investment grade tenants include: (a) investment grade rated tenants; (b) tenants with investment grade rated parent entities that guarantee the tenant's lease obligations; and/or (c) tenants with investment grade rated parent entities that do not guarantee the tenant's lease obligations. Tenants contributing 59.6% of annualized rental income as of March 31, 2026 were investment grade rated (or their payment obligations were guaranteed by an investment grade rated parent) and tenants contributing an additional 0.5% of annualized rental income as of March 31, 2026 were subsidiaries of an investment grade rated parent (although these parent entities are not liable for the payment of rents). Lease related costs generally include capital expenditures used to improve tenants' space or amounts paid directly to tenants to improve their space and leasing related costs, such as brokerage commissions and tenant inducements. Leased square feet is pursuant to leases existing as of March 31, 2026, and includes (i) space being fitted out for tenant occupancy pursuant to OPI's lease agreements, if any, and (ii) space which is leased, but is not occupied or is being offered for sublease by tenants, if any. Square footage measurements are subject to changes when space is remeasured or reconfigured for new tenants. Leasing cost and concession commitments include commitments made for leasing expenditures and concessions, such as tenant improvements, leasing commissions, tenant reimbursements and free rent. Percent leased includes (i) space being fitted out for occupancy pursuant to OPI's lease agreements, if any, and (ii) space which is leased, but is not occupied or is being offered for sublease by tenants, if any, as of the measurement date. REIT is real estate investment trust. Rentable square feet represents total square feet available for lease as of the measurement date. Square footage measurements are subject to changes when space is remeasured or reconfigured for new tenants. Same properties for the three months ended March 31, 2026 is based on properties OPI owned continuously since January 1, 2025; five properties affected by significant redevelopment activities and two properties owned by an unconsolidated joint venture in which OPI owns a 51% interest. Same property cash basis NOI % margin is Same Property Cash Basis NOI as a percentage of same property cash basis rental income. Cash basis rental income excludes non-cash straightline rent adjustments, the net effect of non-cash amortization of intangible lease assets and liabilities and lease termination fees, if any. Same property NOI % margin is Same Property NOI as a percentage of same property rental income. Weighted average remaining lease term is the average remaining lease term in years weighted based on annualized rental income. Non-GAAP Financial Measures and Certain Definitions

RETURN TO TABLE OF CONTENTS Q1 2026 23 Warning Concerning Forward-Looking Statements This presentation contains forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995 and other securities laws that are subject to risks and uncertainties. These statements may include words such as “believe”, “expect”, “anticipate”, “intend”, “plan”, “estimate”, “will”, “may” and negatives or derivatives of these or similar expressions. These forward-looking statements include, among others, statements about: the process and potential outcomes of OPI’s bankruptcy proceedings; OPI’s plan of reorganization and the consummation of the transactions contemplated by such plan; OPI’s ability to continue as a going concern; OPI’s leverage levels; demand for office space; OPI’s future leasing activity, commitments and obligations; economic and market conditions; OPI’s liquidity needs and sources; OPI’s capital expenditure plans and commitments; OPI’s pending or potential dispositions; OPI’s redevelopment and construction activities and plans; and the amount and timing of future distributions. Forward-looking statements reflect OPI’s current expectations, are based on judgments and assumptions, are inherently uncertain and are subject to risks, uncertainties and other factors, which could cause OPI’s actual results, performance or achievements to differ materially from expected future results, performance or achievements expressed or implied in those forward-looking statements. Some of the risks, uncertainties and other factors that may cause OPI’s actual results, performance or achievements to differ materially from those expressed or implied by forward-looking statements include, but are not limited to, the following: OPI’s ability to consummate the transactions contemplated by its plan of reorganization and emerge from bankruptcy; OPI’s ability to comply with the terms of its debt agreements and meet financial covenants; OPI’s ability to make required payments on its debt or refinance its debts as they mature or otherwise become due; OPI’s ability to maintain sufficient liquidity, including the availability of borrowings under its revolving credit facility and its ability to obtain new debt or equity financing, and otherwise manage leverage; OPI’s ability to effectively raise and balance its use of debt and equity capital; whether OPI’s tenants will renew or extend their leases and not exercise early termination options pursuant to their leases or that OPI will obtain replacement tenants on terms as favorable to OPI as its prior leases; the likelihood that OPI’s government tenants will be negatively impacted by government budget constraints, or changes in the use of real estate by government agencies; OPI’s ability to increase or maintain occupancy at its properties on terms desirable to OPI, and OPI’s ability to increase rents when its leases expire or renew; the impact of unfavorable market and commercial real estate industry conditions due to uncertainties surrounding interest rates and high inflation, changing tariffs and trade policies and related uncertainty, supply chain disruptions, volatility in the public equity and debt markets and in commercial real estate markets, generally and in the sectors OPI operate, geopolitical instability and tensions, pandemics, any U.S. government shutdown, economic downturns or a possible recession, labor market conditions or changes in real estate utilization, including continued hybrid and other alternative arrangements, among other things, on OPI and its tenants; OPI’s tenant and geographic concentration; competition within the commercial real estate industry, particularly in those markets in which OPI’s properties are located; OPI’s ability to sell properties at prices it targets, and the timing of such sales; OPI’s ability to manage its capital expenditures and other operating costs effectively and to maintain and enhance its properties and their appeal to tenants; the financial strength of OPI’s tenants; risks and uncertainties regarding the costs and timing of development, redevelopment and repositioning activities, including as a result of prolonged high inflation, cost overruns, supply chain challenges, tariffs, labor shortages, construction delays or inability to obtain necessary permits or volatility in the commercial real estate markets; OPI’s ability to pay distributions to its shareholders; OPI’s ability to acquire properties that realize its targeted returns; the ability of OPI’s manager, RMR, to successfully manage OPI; compliance with, and changes to, federal, state and local laws and regulations, accounting rules, tax laws and similar matters; the impact of any U.S. government shutdown, elimination or reduction of government agencies and programs or failure to increase the government debt ceiling on OPI’S ability to collect rents and pay its operating expenses, debt obligations and distributions to shareholders on a timely basis; actual and potential conflicts of interest with OPI’s related parties, including its Managing Trustees, RMR, Sonesta and others affiliated with them; limitations imposed by and OPI’s ability to satisfy complex rules to maintain OPI’s qualification for taxation as a REIT for U.S. federal income tax purposes; acts of terrorism, outbreaks of pandemics or other public health safety events or conditions, war or other hostilities, global climate change or other manmade or natural disasters beyond OPI’s control, and other matters. These risks, uncertainties and other factors are not exhaustive and should be read in conjunction with other cautionary statements that are included in OPI’s periodic filings. The information contained in OPI’s filings with the SEC, including under the caption “Risk Factors” in its periodic reports, or incorporated therein, identifies important factors that could cause differences from the forward-looking statements in this presentation. OPI’s filings with the SEC are available on the SEC’s website at www.sec.gov. You should not place undue reliance upon OPI’s forward-looking statements. Except as required by law, OPI does not intend to update or change any forward-looking statements as a result of new information, future events or otherwise.