By Paul Barrett, CMIP | The Modern Medicare Agency | Melville, NY 18+ years Medicare-exclusive experience | Licensed in 34 states | 40+ carriers Last updated: June 2026
If you live in Freeport and your doctors are at Mount Sinai South Nassau, stop what you’re doing and read this first.
In 2026, one of the most significant hospital-insurance disputes in New York’s recent memory played out on your doorstep — and if you’re on certain Medicare Advantage plans, it’s still unresolved for you right now. Your neighbors in Valley Stream found out in January that their longtime Mount Sinai doctors were suddenly out-of-network. Some had surgeries scheduled. Some were in active treatment. Nobody warned them until it was almost too late.
That’s what this article is for.
I’ve been helping South Shore Nassau County residents navigate Medicare from my Melville office for 18 years. This isn’t a generic guide about Medicare Advantage. This is the specific, local, real-time intelligence you need to know whether your Medicare plan still opens the doors at One Healthy Way in Oceanside — or closes them.
Why Mount Sinai South Nassau Is Not Optional for South Shore Residents
Let’s start here, because this isn’t just about one hospital.
Mount Sinai South Nassau in Oceanside is the only Level II Trauma Center on Nassau County’s South Shore — verified by the American College of Surgeons. It operates the only stroke center and the only freestanding 9-1-1 receiving Emergency Department in the area. It has 455 beds, more than 900 physicians, and approximately 3,500 employees serving communities from the Rockaways to Massapequa.
In March 2025, they completed a $50 million, five-year renovation that doubled the size of the Emergency Department — from 15,000 to 30,000 square feet, with 54 private exam rooms, centralized nursing stations, and an updated trauma unit with an adjoining radiology bay. The capacity to see approximately 75,000 patients annually. They’re in the middle of a 100,000-square-foot expansion that will add four floors, 40 new ICU beds, and nine operating rooms, with an estimated completion of September 2026.
This is not a community hospital people visit for minor issues and then move on from. For Freeport, Oceanside, Rockville Centre, Valley Stream, Lynbrook, Baldwin, Merrick, and the surrounding South Shore communities, Mount Sinai South Nassau is where people go when things get serious — cardiac events, cancer treatment, strokes, major surgery, trauma.
It earned an ‘A’ for Patient Safety from The Leapfrog Group in the 2026 spring cycle. It received a 2026 Patient Safety Excellence Award from Healthgrades. It has been named to Healthgrades’ 100 Best Hospitals for Coronary Intervention for three consecutive years. It earned 10 U.S. News & World Report “high performing” ratings for conditions including heart attack, heart failure, diabetes, colon surgery, and leukemia/lymphoma/myeloma.
The reason I’m telling you all this is simple: a Medicare Advantage plan that doesn’t cover Mount Sinai South Nassau isn’t a real option for most Freeport-area residents. It’s a liability disguised as coverage.
What Happened Between Anthem and Mount Sinai — The Full Story
This is the most important thing that happened in South Shore Medicare in 2026, and most people heard about it through a letter or a worried conversation with their doctor’s office. Here’s the complete picture.
The Background
Anthem Blue Cross and Blue Shield (formerly known locally as Empire BCBS, now rebranded under Elevance Health) and Mount Sinai Health System had a contract that expired December 31, 2025. Negotiations began in spring 2025. Both sides failed to reach a new agreement.
What Mount Sinai said: “We cannot — and will not — subsidize a for-profit insurer’s margins.” Mount Sinai argued the insurer owed more than $450 million in unpaid claims and was offering reimbursement rates that fell too far below what peer academic medical centers receive.
What Anthem said: Mount Sinai was demanding a 50% rate increase by 2028, “far outpacing inflation,” and seeking provisions that would “drive up unnecessary spending.” Mount Sinai disputed this characterization publicly, stating it sought single-digit annual increases over three years and that Anthem was paying it up to 35% less than comparable New York health systems.
Both sides put their position in writing and went public with it. Neither blinked.
The Timeline
- January 1, 2026: Mount Sinai physicians — all 9,000 of them across New York City and Long Island — exited the Anthem network. For Medicare Advantage members specifically, this meant losing in-network access to their doctors immediately.
- March 4, 2026: Mount Sinai hospitals and facilities — including Mount Sinai South Nassau in Oceanside — exited the Anthem commercial network. This is the date explicitly named in a New York State Civil Service document listing the affected facilities.
- April 13, 2026: Mount Sinai and Anthem reached a new three-year agreement that restored in-network access for most Anthem members.
The critical exception: The April 2026 agreement explicitly and specifically does not cover Anthem Medicare Advantage plans. Mount Sinai’s own statement confirmed this directly: “Please note that this agreement does not include Anthem Medicare Advantage or Anthem Individual Marketplace plans.”
This means that as of today — June 2026 — Anthem Medicare Advantage members still do not have in-network access to Mount Sinai South Nassau. The commercial dispute is resolved. The Medicare Advantage dispute is not.
Sources: choosemountsinai.org (Mount Sinai official communications); keepmountsinai.org (April 2026 resolution announcement); Fierce Healthcare (April 14, 2026); News 12 Long Island; New York State Civil Service (cs.ny.gov), Anthem Blue Cross Mount Sinai update
Who This Affects in Freeport Right Now
If you are currently enrolled in any Anthem Blue Cross Blue Shield Medicare Advantage plan in Nassau County, you do not have in-network access to Mount Sinai South Nassau.
This includes:
- Anthem Medicare Advantage 2 HMO-POS (the 5-star rated plan)
- Any other Anthem Medicare Advantage product in Nassau County
In-network benefits at Mount Sinai South Nassau are not available. Emergency services are covered by law at in-network rates — emergency care is always available regardless of network status. But for everything else — your cardiologist, your oncologist, your orthopedist, your scheduled procedures, your follow-up appointments — you are paying out-of-network rates or finding a different facility.
If you are an Anthem Medicare Advantage member and received care at Mount Sinai South Nassau between January 1 and April 13, 2026: contact Anthem’s member services and ask specifically whether your claims are being reprocessed. The April agreement may affect retroactive claim processing, but Anthem has not publicly confirmed blanket retroactive reprocessing for Medicare Advantage claims.
The Plans That Currently Cover Mount Sinai South Nassau for Medicare
Here is the honest, sourced status of every major Medicare Advantage carrier’s relationship with Mount Sinai South Nassau:
✅ AETNA — In-Network and Strong
Aetna maintains an active network relationship with Mount Sinai South Nassau for Medicare Advantage. An official Mount Sinai Health Partners document explicitly lists Aetna Commercial and Medicare Advantage plans and identifies Mount Sinai South Nassau as a preferred facility. With over 15,740 Nassau County enrollees in the Aetna Medicare Elite PPO alone, Aetna is the most enrolled Medicare Advantage plan in Nassau County — and its South Shore network relationships are part of why.
Aetna’s PPO structure is particularly valuable for South Shore residents: you can see specialists at Mount Sinai South Nassau, Catholic Health’s Mercy Medical in Uniondale, and NYU Langone Hospital on Long Island — all without a referral. For anyone whose care spans multiple South Shore systems, this flexibility is genuinely important.
Always verify your specific physician. While Aetna’s relationship with Mount Sinai South Nassau is confirmed, some individual physicians may bill separately and may not participate in every Aetna plan sub-type. Ask your doctor: “Do you participate in the Aetna Medicare Elite PPO for 2026?” — not just “Do you take Aetna?”
✅ UNITEDHEALTHCARE — In-Network (with a specific caveat)
Standard UHC/Oxford Medicare Advantage plans are in-network with Mount Sinai South Nassau. However, there is one exception every UHC member needs to know: Mount Sinai explicitly does not participate with the UHC Community Plan. This is stated directly on choosemountsinai.org’s accepted insurance plans page.
If you are on any UHC Medicare Advantage plan and see Mount Sinai South Nassau providers, confirm your specific plan is not the Community Plan product. The question to ask: “Does Mount Sinai South Nassau participate in my specific UHC plan — [plan name]?” Not just “Do you take UnitedHealthcare?”
✅ VNS HEALTH — In-Network
VNS Health (formerly Visiting Nurse Service of New York) reached a new agreement with the full Mount Sinai Health System to continue participating in-network through 2026. This is confirmed directly on the choosemountsinai.org official communications page. VNS Health serves a meaningful segment of Nassau’s dual-eligible and lower-income population and the Mount Sinai relationship is intact.
✅ HEALTHFIRST — In-Network (verify individual providers)
Healthfirst maintains a general network relationship with Mount Sinai providers. However, Healthfirst’s network strength on Long Island is considerably more limited than in the five boroughs. Freeport residents should verify each specific physician before enrolling. The question is not whether Healthfirst “covers” Mount Sinai South Nassau in general — it’s whether your particular cardiologist or oncologist participates in the specific Healthfirst plan you’re considering.
⚠️ ANTHEM BLUE CROSS BLUE SHIELD — NOT In-Network for Medicare Advantage
As detailed above: Anthem Medicare Advantage plans are explicitly excluded from the April 2026 Mount Sinai agreement. Not in-network. Emergency services remain covered by federal law. Everything else is out-of-network.
⚠️ WELLCARE — Mount Sinai South Nassau Generally In-Network, But Northwell Is Not
Wellcare’s relationship with Mount Sinai South Nassau is not publicly in dispute as of this writing. However, Wellcare chose not to renew its contract with Northwell Health — the other major health system serving Nassau County — effective July 1, 2026. Some Freeport residents use both South Shore (Mount Sinai South Nassau) and North Shore (Northwell) providers. If you have any Northwell specialists — particularly at Long Island Jewish Medical Center in New Hyde Park — Wellcare’s Northwell exit matters to you directly.
⚠️ HEALTHSPRING (formerly Cigna Medicare) — Mount Sinai South Nassau Generally In-Network, But Northwell Is Not
Same situation as Wellcare on the Northwell side. HealthSpring terminated its relationship with Northwell effective December 31, 2025, covering all Northwell hospitals, physician groups, and ancillary facilities. If you have care split between South Shore and Northwell facilities, verify both.
The Quick Reference Table
Carrier | Mount Sinai South Nassau (MA) | Key Note |
Aetna | ✅ In-Network | Most enrolled plan in Nassau; PPO offers broadest South Shore flexibility |
UnitedHealthcare | ✅ In-Network (standard plans) | ❌ UHC Community Plan NOT accepted — verify your specific plan name |
VNS Health | ✅ In-Network | New 2026 agreement confirmed by Mount Sinai |
Healthfirst | ✅ Generally (verify each provider) | Stronger in boroughs — verify each Long Island physician |
Anthem BCBS | ❌ NOT In-Network (MA) | Apr 2026 agreement excludes Medicare Advantage — unresolved |
Wellcare | ✅ Mount Sinai South Nassau | ❌ Northwell out-of-network as of July 1, 2026 |
HealthSpring | ✅ Mount Sinai South Nassau | ❌ Northwell terminated Dec 31, 2025 |
Medigap (any plan) | ✅ Always covered | Works wherever Medicare is accepted — immune to all network disputes |
Information as of June 2026. Network agreements are subject to change — always verify current status before scheduling non-emergency care.
The Broader Picture: Why This Keeps Happening
The Anthem/Mount Sinai standoff wasn’t a freak occurrence. It’s part of a nationwide pattern that is accelerating.
Becker’s Hospital Review documented 23 major health systems dropping Medicare Advantage plans across the country in 2026 alone. New York-Presbyterian and UnitedHealthcare nearly went out of network in June 2026 without a last-minute agreement. Northwell lost Wellcare and HealthSpring. Fidelis Care and Northwell went through a standoff with a July 15 deadline.
The underlying issue is always the same: Medicare Advantage plans pay hospitals significantly less than traditional Medicare, and the gap is widening. Hospitals reach a point where they look at what they’re paid versus what care actually costs, and the math stops working.
Here’s what that means for you as a consumer: a plan that covers your hospital today may not cover it next January. Network stability is not guaranteed. And for people on fixed incomes with serious health conditions and established relationships with specific doctors, that instability has real, serious consequences.
The Option That Is Immune to All of This
I want to be direct about something, because it’s what I’d tell a family member.
Every hospital-insurance dispute you’ve read about in this article — Anthem and Mount Sinai, Wellcare and Northwell, HealthSpring and Northwell, Fidelis and Northwell — affects only Medicare Advantage members.
Medigap members are entirely unaffected by all of them.
Here’s why: A Medicare Supplement (Medigap) plan works alongside Original Medicare, not as a replacement for it. It covers the gaps — the 20% coinsurance, the hospital deductibles — that Original Medicare leaves behind. Because your coverage is through Original Medicare, any provider in the country who accepts Medicare accepts your Medigap plan.
Mount Sinai South Nassau accepts Original Medicare. Therefore, with any Medigap plan, Mount Sinai South Nassau is covered. If Anthem and Mount Sinai go to war again next January, it doesn’t affect you. If some other carrier drops out of the Mount Sinai network next AEP, it doesn’t affect you. The protection is structural, not dependent on a contract that’s up for renegotiation every few years.
The trade-off is real: Medigap on Long Island is expensive. Plan G through UHC — the lowest-priced carrier — runs $372.50/month for 2026. Add the $283 Part B deductible and a Part D plan, and your minimum annual commitment exceeds $5,000 before you use a medical service.
But for someone managing cancer treatment at Mount Sinai South Nassau’s Feil Cancer Center, or recovering from cardiac intervention after a procedure at their newly expanded ER, or seeing a specialist who has treated them for years — the math may look very different when you weigh the monthly premium against the uncertainty of Medicare Advantage network stability in 2026.
New York also gives you a right most Americans don’t have: you can switch from Medicare Advantage to Medigap at any time of year, with no medical underwriting, regardless of your health. That option is open to you today.
For a full breakdown of what Medigap actually costs on Long Island and which carriers are genuinely available, see our Medicare Supplement Plans in Freeport, NY: 2026 Rates and What NY’s Rules Mean for You.
What To Do Right Now If You're Affected
If you’re on an Anthem Medicare Advantage plan:
- Call Anthem’s member services at the number on your card and ask specifically: “Is Mount Sinai South Nassau in-network for my plan?” Get the answer in writing or note the date, time, and representative’s name.
- Call Mount Sinai South Nassau’s insurance department at (516) 632-3000 and ask whether your specific Anthem plan is currently accepted for non-emergency care.
- If you have upcoming procedures, appointments, or ongoing treatment — call my office at 631-358-5793 before that appointment. You may have options you don’t know about.
- You cannot currently make a mid-year plan change solely because Anthem doesn’t cover Mount Sinai Medicare Advantage — but your specific circumstances (active treatment, chronic condition, upcoming procedure) may qualify you for a Special Enrollment Period. Don’t assume. Call and ask.
If you’re considering a new Medicare Advantage plan and use Mount Sinai South Nassau:
Before you look at a single premium, give me the name of your doctor. I’ll run a live network check against every plan available in Nassau County. Not a general “does this carrier cover Mount Sinai” search — a specific check for your physician, your plan type, and your zip code. That’s the only check that actually matters.
If you’re currently on Medigap:
You’re protected from everything in this article. Original Medicare plus your supplement plan means Mount Sinai South Nassau — and any other Medicare-accepting facility in the country — is available to you. Review your Part D coverage annually, make sure your rates are still competitive, and call me if your premium has spiked.
Frequently Asked Questions
No. Anthem Medicare Advantage plans are explicitly excluded from the April 2026 agreement between Anthem and Mount Sinai Health System. Mount Sinai South Nassau — as part of the Mount Sinai Health System — is not in-network for Anthem Medicare Advantage as of June 2026. Emergency services remain covered at in-network rates by federal law. For all other care, Anthem Medicare Advantage members face out-of-network cost-sharing at Mount Sinai South Nassau.
Anthem and Mount Sinai failed to renew their contract by December 31, 2025. Mount Sinai physicians — approximately 9,000 across New York City and Long Island — left the Anthem network January 1, 2026. Mount Sinai hospitals, including South Nassau, exited March 4, 2026. A new three-year agreement was reached April 13, 2026 — but it explicitly excludes Medicare Advantage and Individual Marketplace plans. The dispute centered on reimbursement: Anthem claimed Mount Sinai sought a 50% rate increase by 2028, which Mount Sinai publicly disputed, stating it sought single-digit annual increases and that Anthem was paying it up to 35% below comparable New York health systems. Mount Sinai also stated Anthem owed over $450 million in unpaid claims for care already delivered.
Aetna Medicare Advantage plans maintain an active in-network relationship with Mount Sinai South Nassau. Standard UHC/Oxford Medicare Advantage plans (not the Community Plan) are in-network. VNS Health reached a new 2026 agreement with Mount Sinai. Healthfirst generally participates, but individual provider verification is essential given their thinner Long Island network.
Yes. Federal law requires Medicare Advantage plans to cover emergency services at in-network cost-sharing rates regardless of network status. If you have a genuine emergency, go to Mount Sinai South Nassau — your plan must cover it as in-network. The network dispute affects non-emergency scheduled care.
Possibly. If your Anthem Medicare Advantage plan’s loss of Mount Sinai access constitutes a significant disruption to your ongoing care, you may qualify for a Special Enrollment Period. Eligibility depends on your specific situation — active treatment, chronic conditions, upcoming procedures all matter. Call me at 631-358-5793 and I’ll review your circumstances at no charge.
Yes — completely. Medigap plans work alongside Original Medicare, which means any provider who accepts Medicare accepts your coverage. Mount Sinai South Nassau accepts Original Medicare. Network disputes between carriers and hospitals don’t affect Medigap members. In New York, you can switch from Medicare Advantage to Medigap any time of year without medical underwriting. If network instability concerns you, that option is worth a serious conversation.
Mount Sinai South Nassau joined the Mount Sinai Health System in 2018 and is the system’s Long Island flagship hospital — the only Mount Sinai facility outside New York City. It’s fully integrated into the Mount Sinai Health System clinically, which means patients have access to the system’s broader specialist network and research resources. It also means that system-level contract disputes — like the Anthem situation — affect South Nassau as part of the system, not separately.
If your plan representative told you Mount Sinai South Nassau is in-network for your Anthem Medicare Advantage plan after April 13, 2026 — get that confirmation in writing, with a reference number. The April agreement specifically excluded Medicare Advantage. If there has been a separate, more recent agreement specifically covering Medicare Advantage that was not publicly announced as of this writing, Mount Sinai’s own website at choosemountsinai.org will reflect it. Check there directly for the most current status.
Ready for an Honest Conversation?
I serve Freeport, Oceanside, Rockville Centre, Valley Stream, Lynbrook, Baldwin, Merrick, and all of Nassau County’s South Shore from my office in Melville. If you’re worried about your Mount Sinai access, if you’re on an Anthem plan and trying to figure out your options, or if you’ve never had someone sit down and actually check your specific doctors against your specific plan — call me.
No scripts. No pressure. No disappearing after you enroll.
Just honest guidance from someone who has been doing this on the South Shore for 18 years and is still answering calls in February when questions come up.
Paul Barrett, CMIP The Modern Medicare Agency 📞 631-358-5793 ✉️ medicare@paulbinsurance.com 🌐 paulbinsurance.com 📍 445 Broad Hollow Rd, Melville, NY 11747
Serving Freeport and Nassau County’s South Shore since 2007
Related reading:
- Medicare Advantage Plans in Freeport, NY: Your Honest 2026 Local Guide
- Medicare Supplement Plans in Freeport, NY: 2026 Rates and What NY’s Rules Mean for You
- Medigap vs. Medicare Advantage in Freeport, NY: Your 2026 Comparison Guide
- Northwell Health and Medicare in Farmingdale: Which Plans Cover Your Doctors in 2026
- Medicare Advantage Plans in Farmingdale, NY: Your Honest 2026 Local Guide
Primary sources:
- Mount Sinai Health System — Official Anthem Communications (choosemountsinai.org)
- Keep Mount Sinai — April 2026 Agreement Announcement (excludes Medicare Advantage)
- Mount Sinai South Nassau — Insurance Plans
- Mount Sinai South Nassau — About the Hospital
- Fierce Healthcare — Anthem Mount Sinai Agreement, April 14, 2026
- Long Island Herald — Mount Sinai South Nassau Named Specifically, January 2026
- CBS New York — 9,000 Physicians and 200,000 Anthem Patients Affected
- NBC News — $450 Million Unpaid Claims, Rate Increase Dispute
- Long Island Press — $50 Million ER Renovation Opens March 2025
- Healthcare Facilities Today — Feil Family Pavilion Details
- Northwell Health — Wellcare Network Update
- CMS Medicare Advantage Enrollment Data 2026
Disclaimer: The Modern Medicare Agency is not connected with or endorsed by the United States government or the federal Medicare program. Network participation status reflects publicly available information as of June 2026 and is subject to change. Always verify your specific plan’s network status directly with your carrier and provider before scheduling non-emergency care. We do not offer every plan available in your area.
