From 3ec800f29defca030575ae332bc7c6bb5a739a97 Mon Sep 17 00:00:00 2001
From: Lukas Devos <ldevos98@gmail.com>
Date: Sun, 22 Feb 2026 17:47:40 -0500
Subject: [PATCH 01/14] Revert "Adapt extension (#384)"

This reverts commit 2db4cb1abd1132c9d5e10990a7fc0fd06ba08c6b.
---
 Project.toml                     | 10 +-----
 ext/MPSKitAdaptExt.jl            | 57 --------------------------------
 src/operators/jordanmpotensor.jl | 12 +++----
 src/states/abstractmps.jl        |  1 -
 src/states/finitemps.jl          |  3 ++
 test/operators/mpo.jl            | 26 +--------------
 test/operators/mpohamiltonian.jl | 35 +-------------------
 7 files changed, 12 insertions(+), 132 deletions(-)
 delete mode 100644 ext/MPSKitAdaptExt.jl

diff --git a/Project.toml b/Project.toml
index 9b39e662f..0ba745a7f 100644
--- a/Project.toml
+++ b/Project.toml
@@ -23,15 +23,8 @@ TensorKitManifolds = "11fa318c-39cb-4a83-b1ed-cdc7ba1e3684"
 TensorOperations = "6aa20fa7-93e2-5fca-9bc0-fbd0db3c71a2"
 VectorInterface = "409d34a3-91d5-4945-b6ec-7529ddf182d8"
 
-[weakdeps]
-Adapt = "79e6a3ab-5dfb-504d-930d-738a2a938a0e"
-
-[extensions]
-MPSKitAdaptExt = "Adapt"
-
 [compat]
 Accessors = "0.1"
-Adapt = "4"
 Aqua = "0.8.9"
 BlockTensorKit = "0.3.4"
 Combinatorics = "1"
@@ -60,7 +53,6 @@ VectorInterface = "0.2, 0.3, 0.4, 0.5"
 julia = "1.10"
 
 [extras]
-Adapt = "79e6a3ab-5dfb-504d-930d-738a2a938a0e"
 Aqua = "4c88cf16-eb10-579e-8560-4a9242c79595"
 Combinatorics = "861a8166-3701-5b0c-9a16-15d98fcdc6aa"
 ParallelTestRunner = "d3525ed8-44d0-4b2c-a655-542cee43accc"
@@ -71,4 +63,4 @@ Test = "8dfed614-e22c-5e08-85e1-65c5234f0b40"
 TestExtras = "5ed8adda-3752-4e41-b88a-e8b09835ee3a"
 
 [targets]
-test = ["Aqua", "Adapt", "Pkg", "Test", "TestExtras", "Plots", "Combinatorics", "ParallelTestRunner", "TensorKitTensors"]
+test = ["Aqua", "Pkg", "Test", "TestExtras", "Plots", "Combinatorics", "ParallelTestRunner", "TensorKitTensors"]
diff --git a/ext/MPSKitAdaptExt.jl b/ext/MPSKitAdaptExt.jl
deleted file mode 100644
index c6e16fd76..000000000
--- a/ext/MPSKitAdaptExt.jl
+++ /dev/null
@@ -1,57 +0,0 @@
-module MPSKitAdaptExt
-
-using TensorKit: space, spacetype
-using MPSKit
-using BlockTensorKit: nonzero_pairs
-using Adapt
-
-function Adapt.adapt_structure(to, mps::FiniteMPS)
-    ad = adapt(to)
-    adapt_not_missing(x) = ismissing(x) ? x : ad(x)
-
-    TA = Base.promote_op(ad, MPSKit.site_type(mps))
-    TB = Base.promote_op(ad, MPSKit.bond_type(mps))
-
-    ALs = map!(adapt_not_missing, similar(mps.ALs, Union{Missing, TA}), mps.ALs)
-    ARs = map!(adapt_not_missing, similar(mps.ARs, Union{Missing, TA}), mps.ARs)
-    ACs = map!(adapt_not_missing, similar(mps.ACs, Union{Missing, TA}), mps.ACs)
-    Cs = map!(adapt_not_missing, similar(mps.Cs, Union{Missing, TB}), mps.Cs)
-
-    return FiniteMPS{TA, TB}(ALs, ARs, ACs, Cs)
-end
-
-function Adapt.adapt_structure(to, mps::InfiniteMPS)
-    ad = adapt(to)
-    AL = map(ad, mps.AL)
-    AR = map(ad, mps.AR)
-    C = map(ad, mps.C)
-    AC = map(ad, mps.AC)
-
-    return InfiniteMPS{eltype(AL), eltype(C)}(AL, AR, C, AC)
-end
-
-Adapt.adapt_structure(to, mpo::MPO) = MPO(map(adapt(to), mpo.O))
-
-function Adapt.adapt_structure(::Type{TorA}, W::MPSKit.JordanMPOTensor) where {TorA <: Union{Number, DenseVector{<:Number}}}
-    TT = MPSKit.jordanmpotensortype(spacetype(W), TorA)
-    W′ = TT(undef, space(W))
-    ad = adapt(TorA)
-
-    for (k, v) in nonzero_pairs(W.A)
-        W′.A[k] = ad(v)
-    end
-    for (k, v) in nonzero_pairs(W.B)
-        W′.B[k] = ad(v)
-    end
-    for (k, v) in nonzero_pairs(W.C)
-        W′.C[k] = ad(v)
-    end
-    for (k, v) in nonzero_pairs(W.D)
-        W′.D[k] = ad(v)
-    end
-
-    return W′
-end
-Adapt.adapt_structure(to, mpo::MPOHamiltonian) = MPOHamiltonian(map(adapt(to), mpo.W))
-
-end
diff --git a/src/operators/jordanmpotensor.jl b/src/operators/jordanmpotensor.jl
index 02f36c987..4a3dbe798 100644
--- a/src/operators/jordanmpotensor.jl
+++ b/src/operators/jordanmpotensor.jl
@@ -121,12 +121,12 @@ function JordanMPOTensor(W::SparseBlockTensorMap{TT, E, S, 2, 2}) where {TT, E,
     )
 end
 
-function jordanmpotensortype(::Type{S}, ::Type{TorA}) where {S <: VectorSpace, TorA}
-    TA = Union{tensormaptype(S, 2, 2, TorA), BraidingTensor{scalartype(TorA), S}}
-    TB = tensormaptype(S, 2, 1, TorA)
-    TC = tensormaptype(S, 1, 2, TorA)
-    TD = tensormaptype(S, 1, 1, TorA)
-    return JordanMPOTensor{scalartype(TorA), S, TA, TB, TC, TD}
+function jordanmpotensortype(::Type{S}, ::Type{E}) where {S <: VectorSpace, E <: Number}
+    TA = Union{tensormaptype(S, 2, 2, E), BraidingTensor{E, S}}
+    TB = tensormaptype(S, 2, 1, E)
+    TC = tensormaptype(S, 1, 2, E)
+    TD = tensormaptype(S, 1, 1, E)
+    return JordanMPOTensor{E, S, TA, TB, TC, TD}
 end
 function jordanmpotensortype(::Type{O}) where {O <: MPOTensor}
     return jordanmpotensortype(spacetype(O), scalartype(O))
diff --git a/src/states/abstractmps.jl b/src/states/abstractmps.jl
index b80cdcc1c..3d277aff4 100644
--- a/src/states/abstractmps.jl
+++ b/src/states/abstractmps.jl
@@ -199,7 +199,6 @@ TensorKit.spacetype(ψ::AbstractMPS) = spacetype(typeof(ψ))
 TensorKit.spacetype(ψtype::Type{<:AbstractMPS}) = spacetype(site_type(ψtype))
 TensorKit.sectortype(ψ::AbstractMPS) = sectortype(typeof(ψ))
 TensorKit.sectortype(ψtype::Type{<:AbstractMPS}) = sectortype(site_type(ψtype))
-TensorKit.storagetype(ψtype::Type{<:AbstractMPS}) = storagetype(site_type(ψtype))
 
 """
     left_virtualspace(ψ::AbstractMPS, [pos=1:length(ψ)])
diff --git a/src/states/finitemps.jl b/src/states/finitemps.jl
index 1c294ae90..755825c74 100644
--- a/src/states/finitemps.jl
+++ b/src/states/finitemps.jl
@@ -376,6 +376,9 @@ end
 
 site_type(::Type{<:FiniteMPS{A}}) where {A} = A
 bond_type(::Type{<:FiniteMPS{<:Any, B}}) where {B} = B
+function TensorKit.storagetype(::Union{MPS, Type{MPS}}) where {A, MPS <: FiniteMPS{A}}
+    return storagetype(A)
+end
 
 function left_virtualspace(ψ::FiniteMPS, n::Integer)
     checkbounds(ψ, n)
diff --git a/test/operators/mpo.jl b/test/operators/mpo.jl
index 34f2553db..4f6d2cad9 100644
--- a/test/operators/mpo.jl
+++ b/test/operators/mpo.jl
@@ -4,8 +4,8 @@ println("
 --------------------
 ")
 
+using .TestSetup
 using Test, TestExtras
-using Adapt
 using MPSKit
 using MPSKit: GeometryStyle, FiniteChainStyle, InfiniteChainStyle, OperatorStyle, MPOStyle
 using TensorKit
@@ -83,7 +83,6 @@ using TensorKit: ℙ
     end
 end
 
-
 @testset "InfiniteMPO" begin
     P = ℂ^2
     T = Float64
@@ -99,26 +98,3 @@ end
     @test OperatorStyle(typeof(H)) == MPOStyle()
     @test OperatorStyle(H) == MPOStyle()
 end
-
-@testset "Adapt" for V in (ℂ^2, U1Space(-1 => 1, 0 => 1, 1 => 1))
-    L = 3
-    o = rand(Float32, V^L ← V^L)
-    mpo1 = FiniteMPO(o)
-    for T in (Float64, ComplexF64)
-        mpo2 = @testinferred adapt(Vector{T}, mpo1)
-        @test mpo2 isa FiniteMPO
-        @test scalartype(mpo2) == T
-        @test storagetype(mpo2) == Vector{T}
-        @test convert(TensorMap, mpo2) ≈ o
-    end
-
-    mpo3 = InfiniteMPO(mpo1[2:2])
-    for T in (Float64, ComplexF64)
-        mpo4 = @testinferred adapt(Vector{T}, mpo3)
-        @test mpo4 isa InfiniteMPO
-        @test scalartype(mpo4) == T
-        @test storagetype(mpo4) == Vector{T}
-        @test dot(mpo3, mpo4) ≈ 1 atol = 1.0e-4
-    end
-
-end
diff --git a/test/operators/mpohamiltonian.jl b/test/operators/mpohamiltonian.jl
index 7eae64ea9..666ab2bee 100644
--- a/test/operators/mpohamiltonian.jl
+++ b/test/operators/mpohamiltonian.jl
@@ -4,8 +4,8 @@ println("
 ----------------------------
 ")
 
+using .TestSetup
 using Test, TestExtras
-using Adapt
 using MPSKit
 using MPSKit: GeometryStyle, FiniteChainStyle, InfiniteChainStyle, OperatorStyle, HamiltonianStyle
 using TensorKit
@@ -239,36 +239,3 @@ end
     h4 = H4 * H4
     @test real(expectation_value(ψ2, H4)) >= 0
 end
-
-@testset "Adapt" for V in (ℂ^2, U1Space(-1 => 1, 0 => 1, 1 => 1))
-    h = rand(Float32, V^2 ← V^2)
-    h += h'
-
-    L = 4
-    H1 = FiniteMPOHamiltonian(
-        fill(V, L),
-        ((i, i + 1) => h for i in 1:(L - 1))...,
-        ((i, i + 2) => h for i in 1:(L - 2))...,
-        ((i, i + 3) => h for i in 1:(L - 3))...,
-    )
-    mps1 = FiniteMPS(physicalspace(H1), oneunit(V))
-
-    for T in (Float64, ComplexF64)
-        H2 = @testinferred adapt(Vector{T}, H1)
-        @test H2 isa FiniteMPOHamiltonian
-        @test scalartype(H2) == T
-        @test storagetype(H2) == Vector{T}
-        @test expectation_value(mps1, H1) ≈ expectation_value(mps1, H2)
-    end
-
-    H3 = InfiniteMPOHamiltonian(fill(V, L), (1, 2) => h, (1, 3) => h, (1, 4) => h)
-    mps2 = InfiniteMPS(physicalspace(H3), [oneunit(V)])
-    for T in (Float64, ComplexF64)
-        H4 = @testinferred adapt(Vector{T}, H3)
-        @test H4 isa InfiniteMPOHamiltonian
-        @test scalartype(H4) == T
-        @test storagetype(H4) == Vector{T}
-        @test expectation_value(mps2, H3) ≈ expectation_value(mps2, H4)
-    end
-
-end

From 1b310ff2ec59a1fcdd9ad56456a7432c2e295399 Mon Sep 17 00:00:00 2001
From: Akshay Shankar <sakshays.2000@gmail.com>
Date: Mon, 23 Feb 2026 17:58:58 +0100
Subject: [PATCH 02/14] Deep copying MPS with copy (#387)

* broadcast copy over arrays

* add basic tests for copying mps

* fix variable naming mismatch

* small fixes

* format

---------

Co-authored-by: Lukas Devos <ldevos98@gmail.com>
---
 src/states/finitemps.jl          | 15 +++++++++++++--
 src/states/infinitemps.jl        |  2 +-
 test/operators/mpo.jl            |  1 +
 test/operators/mpohamiltonian.jl |  1 +
 test/states/finitemps.jl         | 30 +++++++++++++++++++++++++++++-
 test/states/infinitemps.jl       | 27 ++++++++++++++++++++++++++-
 6 files changed, 71 insertions(+), 5 deletions(-)

diff --git a/src/states/finitemps.jl b/src/states/finitemps.jl
index 755825c74..c956b9730 100644
--- a/src/states/finitemps.jl
+++ b/src/states/finitemps.jl
@@ -305,7 +305,6 @@ Utility
 Base.size(ψ::FiniteMPS, args...) = size(ψ.ALs, args...)
 Base.length(ψ::FiniteMPS) = length(ψ.ALs)
 Base.eltype(ψtype::Type{<:FiniteMPS}) = site_type(ψtype) # this might not be true
-Base.copy(ψ::FiniteMPS) = FiniteMPS(copy(ψ.ALs), copy(ψ.ARs), copy(ψ.ACs), copy(ψ.Cs))
 function Base.similar(ψ::FiniteMPS{A, B}) where {A, B}
     return FiniteMPS{A, B}(similar(ψ.ALs), similar(ψ.ARs), similar(ψ.ACs), similar(ψ.Cs))
 end
@@ -338,7 +337,19 @@ end
 # TODO: check where gauge center is to determine efficient kind
 AC2(psi::FiniteMPS, site::Int) = psi.AC[site] * _transpose_tail(psi.AR[site + 1])
 
-_complex_if_not_missing(x) = ismissing(x) ? x : complex(x)
+f_if_not_missing(f, x) = ismissing(x) ? x : f(x)
+_copy_if_not_missing(x) = f_if_not_missing(copy, x)
+_complex_if_not_missing(x) = f_if_not_missing(complex, x)
+
+function Base.copy(mps::FiniteMPS)
+    mps2 = similar(mps)
+    mps2.ALs .= _copy_if_not_missing.(mps.ALs)
+    mps2.ARs .= _copy_if_not_missing.(mps.ARs)
+    mps2.ACs .= _copy_if_not_missing.(mps.ACs)
+    mps2.Cs .= _copy_if_not_missing.(mps.Cs)
+    return mps2
+end
+
 function Base.complex(mps::FiniteMPS)
     scalartype(mps) <: Complex && return mps
     ALs = _complex_if_not_missing.(mps.ALs)
diff --git a/src/states/infinitemps.jl b/src/states/infinitemps.jl
index 8e3780ad3..1cd07bab4 100644
--- a/src/states/infinitemps.jl
+++ b/src/states/infinitemps.jl
@@ -244,7 +244,7 @@ Base.eltype(::Type{<:InfiniteMPS{A}}) where {A} = A
 Base.isfinite(::Type{<:InfiniteMPS}) = false
 GeometryStyle(::Type{<:InfiniteMPS}) = InfiniteChainStyle()
 
-Base.copy(ψ::InfiniteMPS) = InfiniteMPS(copy(ψ.AL), copy(ψ.AR), copy(ψ.C), copy(ψ.AC))
+Base.copy(ψ::InfiniteMPS) = InfiniteMPS(copy.(ψ.AL), copy.(ψ.AR), copy.(ψ.C), copy.(ψ.AC))
 function Base.copy!(ψ::InfiniteMPS, ϕ::InfiniteMPS)
     ψ.AL .= _copy!!.(ψ.AL, ϕ.AL)
     ψ.AR .= _copy!!.(ψ.AR, ϕ.AR)
diff --git a/test/operators/mpo.jl b/test/operators/mpo.jl
index 4f6d2cad9..c73608c6d 100644
--- a/test/operators/mpo.jl
+++ b/test/operators/mpo.jl
@@ -10,6 +10,7 @@ using MPSKit
 using MPSKit: GeometryStyle, FiniteChainStyle, InfiniteChainStyle, OperatorStyle, MPOStyle
 using TensorKit
 using TensorKit: ℙ
+using Adapt
 
 @testset "FiniteMPO" begin
     # start from random operators
diff --git a/test/operators/mpohamiltonian.jl b/test/operators/mpohamiltonian.jl
index 666ab2bee..9ff79f4c1 100644
--- a/test/operators/mpohamiltonian.jl
+++ b/test/operators/mpohamiltonian.jl
@@ -10,6 +10,7 @@ using MPSKit
 using MPSKit: GeometryStyle, FiniteChainStyle, InfiniteChainStyle, OperatorStyle, HamiltonianStyle
 using TensorKit
 using TensorKit: ℙ
+using Adapt
 
 pspaces = (ℙ^4, Rep[U₁](0 => 2), Rep[SU₂](1 => 1))
 vspaces = (ℙ^10, Rep[U₁]((0 => 20)), Rep[SU₂](1 // 2 => 10, 3 // 2 => 5, 5 // 2 => 1))
diff --git a/test/states/finitemps.jl b/test/states/finitemps.jl
index d23e26343..d45170437 100644
--- a/test/states/finitemps.jl
+++ b/test/states/finitemps.jl
@@ -5,12 +5,12 @@ println("
 ")
 
 using Test, TestExtras
-using Adapt
 using MPSKit
 using MPSKit: _transpose_front, _transpose_tail
 using MPSKit: GeometryStyle, FiniteChainStyle
 using TensorKit
 using TensorKit: ℙ
+using Adapt
 
 @testset "FiniteMPS ($(sectortype(D)), $elt)" for (D, d, elt) in [
         (ℙ^10, ℙ^2, ComplexF64),
@@ -113,3 +113,31 @@ end
     @test ψ.center == 13 / 2
     @test ψ[5:7] == [ψ.ALs[5], ψ.ACs[6], ψ.ARs[7]]
 end
+
+@testset "FiniteMPS copying" begin
+    L = 10
+    mps1 = FiniteMPS(rand, ComplexF64, L, ℂ^2, ℂ^5)
+    mps2 = copy(mps1)
+
+    @test mps1 !== mps2
+
+    # arrays are distinct
+    @test mps1.ALs !== mps2.ALs
+    @test mps1.ARs !== mps2.ARs
+    @test mps1.ACs !== mps2.ACs
+    @test mps1.Cs !== mps2.Cs
+
+    # tensors are distinct but equal
+    for i in 1:L
+        @test (ismissing(mps1.ALs[i]) && ismissing(mps2.ALs[i])) ||
+            (mps1.ALs[i] !== mps2.ALs[i] && mps1.ALs[i] == mps2.ALs[i])
+        @test (ismissing(mps1.ARs[i]) && ismissing(mps2.ARs[i])) ||
+            (mps1.ARs[i] !== mps2.ARs[i] && mps1.ARs[i] == mps2.ARs[i])
+        @test (ismissing(mps1.ACs[i]) && ismissing(mps2.ACs[i])) ||
+            (mps1.ACs[i] !== mps2.ACs[i] && mps1.ACs[i] == mps2.ACs[i])
+        @test (ismissing(mps1.Cs[i]) && ismissing(mps2.Cs[i])) ||
+            (mps1.Cs[i] !== mps2.Cs[i] && mps1.Cs[i] == mps2.Cs[i])
+    end
+    @test (ismissing(mps1.Cs[end]) && ismissing(mps2.Cs[end])) ||
+        mps1.Cs[end] !== mps2.Cs[end]
+end
diff --git a/test/states/infinitemps.jl b/test/states/infinitemps.jl
index 0ac4e269c..ee032dd17 100644
--- a/test/states/infinitemps.jl
+++ b/test/states/infinitemps.jl
@@ -5,11 +5,11 @@ println("
 ")
 
 using Test, TestExtras
-using Adapt
 using MPSKit
 using MPSKit: GeometryStyle, InfiniteChainStyle, TransferMatrix
 using TensorKit
 using TensorKit: ℙ
+using Adapt
 
 @testset "InfiniteMPS ($(sectortype(D)), $elt)" for (D, d, elt) in
     [(ℙ^10, ℙ^2, ComplexF64), (Rep[U₁](1 => 3), Rep[U₁](0 => 1), ComplexF64)]
@@ -46,6 +46,31 @@ using TensorKit: ℙ
     end
 end
 
+@testset "InfiniteMPS copying" begin
+    mps1 = InfiniteMPS(rand, ComplexF64, ℂ^2, ℂ^5)
+    mps2 = copy(mps1)
+
+    @test mps1 !== mps2
+
+    # elements are equal
+    @test mps1.AL[1] == mps2.AL[1]
+    @test mps1.AR[1] == mps2.AR[1]
+    @test mps1.AC[1] == mps2.AC[1]
+    @test mps1.C[1] == mps2.C[1]
+
+    # arrays are distinct
+    @test mps1.AL !== mps2.AL
+    @test mps1.AR !== mps2.AR
+    @test mps1.AC !== mps2.AC
+    @test mps1.C !== mps2.C
+
+    # tensors are distinct
+    @test mps1.AL[1] !== mps2.AL[1]
+    @test mps1.AR[1] !== mps2.AR[1]
+    @test mps1.AC[1] !== mps2.AC[1]
+    @test mps1.C[1] !== mps2.C[1]
+end
+
 @testset "Adapt" begin
     for (d, D) in [(ℂ^2, ℂ^4), (ℙ^2, ℙ^4)]
         mps1 = InfiniteMPS(rand, Float32, d, D)

From d9f275e2eec5e1f65b90d68d3b0aad003fbbb837 Mon Sep 17 00:00:00 2001
From: Andreas Feuerpfeil <andreas.feuerpfeil@gmail.com>
Date: Mon, 23 Feb 2026 20:39:42 +0100
Subject: [PATCH 03/14] Refactor entropy function to also use spectrum directly
 (#377)

* Refactor entropy function to also use spectrum directly

* specialize to SectorVector and add test

* add infinite test

* update docstring

---------

Co-authored-by: Lukas Devos <ldevos98@gmail.com>
---
 src/algorithms/toolbox.jl  | 21 +++++++++++++++------
 test/states/finitemps.jl   | 31 +++++++++++++++++++++++++++++++
 test/states/infinitemps.jl | 22 ++++++++++++++++++++++
 3 files changed, 68 insertions(+), 6 deletions(-)

diff --git a/src/algorithms/toolbox.jl b/src/algorithms/toolbox.jl
index 4956d163c..4f548dada 100644
--- a/src/algorithms/toolbox.jl
+++ b/src/algorithms/toolbox.jl
@@ -1,15 +1,24 @@
 """
     entropy(state, [site::Int])
+    entropy(spectrum::SectorVector)
 
-Calculate the von Neumann entanglement entropy of a given MPS. If an integer `site` is
-given, the entropy is across the entanglement cut to the right of site `site`. Otherwise, a
-vector of entropies is returned, one for each site.
+Calculate the von Neumann entanglement entropy. The entropy can be computed from either an
+MPS state or directly from an entanglement spectrum as obtained from
+[`entanglement_spectrum`](@ref).
+
+When called on an MPS with an integer `site`, the entropy is computed across the
+entanglement cut to the right of site `site`. For `InfiniteMPS`, omitting `site` returns a
+vector of entropies, one for each site. For `FiniteMPS` and `WindowMPS`, `site` is
+required.
 """
 entropy(state::InfiniteMPS) = map(Base.Fix1(entropy, state), 1:length(state))
 function entropy(state::Union{FiniteMPS, WindowMPS, InfiniteMPS}, loc::Int)
-    S = zero(real(scalartype(state)))
-    tol = eps(typeof(S))
-    for (c, b) in pairs(entanglement_spectrum(state, loc))
+    return entropy(entanglement_spectrum(state, loc))
+end
+function entropy(spectrum::TensorKit.SectorVector{T}) where {T}
+    S = zero(T)
+    tol = eps(T)
+    for (c, b) in pairs(spectrum)
         s = zero(S)
         for x in b
             x < tol && break
diff --git a/test/states/finitemps.jl b/test/states/finitemps.jl
index d45170437..1cc2a4ea2 100644
--- a/test/states/finitemps.jl
+++ b/test/states/finitemps.jl
@@ -141,3 +141,34 @@ end
     @test (ismissing(mps1.Cs[end]) && ismissing(mps2.Cs[end])) ||
         mps1.Cs[end] !== mps2.Cs[end]
 end
+
+@testset "FiniteMPS entropy ($(sectortype(D)), $elt)" for (D, d, elt) in [
+        (ℙ^10, ℙ^2, ComplexF64),
+        (
+            Rep[U₁](-1 => 3, 0 => 3, 1 => 3),
+            Rep[U₁](-1 => 1, 0 => 1, 1 => 1),
+            ComplexF64,
+        ),
+    ]
+    L = 6
+    ψ = FiniteMPS(rand, elt, L, d, D)
+
+    # entropy is non-negative at all sites
+    for site in 1:L
+        @test real(entropy(ψ, site)) >= 0
+    end
+
+    # entropy is consistent with entanglement_spectrum
+    for site in 1:L
+        @test entropy(ψ, site) ≈ entropy(entanglement_spectrum(ψ, site))
+    end
+
+    # entropy is zero at the right boundary (trivial bond)
+    @test entropy(ψ, L) ≈ 0 atol = 1.0e-10
+
+    # product state has zero entropy everywhere
+    ψ_product = FiniteMPS(rand, elt, L, d, oneunit(D))
+    for site in 1:L
+        @test entropy(ψ_product, site) ≈ 0 atol = 1.0e-10
+    end
+end
diff --git a/test/states/infinitemps.jl b/test/states/infinitemps.jl
index ee032dd17..7f2cc6b62 100644
--- a/test/states/infinitemps.jl
+++ b/test/states/infinitemps.jl
@@ -83,3 +83,25 @@ end
         end
     end
 end
+
+@testset "InfiniteMPS entropy ($(sectortype(D)), $elt)" for (D, d, elt) in
+    [(ℙ^10, ℙ^2, ComplexF64), (Rep[U₁](1 => 3), Rep[U₁](0 => 1), ComplexF64)]
+    ψ = InfiniteMPS([d, d], [D, D])
+
+    # entropy(ψ) returns one value per site, all non-negative
+    Ss = entropy(ψ)
+    @test length(Ss) == length(ψ)
+    @test all(isreal, Ss)
+    @test all(>=(0), Ss)
+
+    # entropy(ψ, site) is non-negative and consistent with entropy(ψ)
+    for site in 1:length(ψ)
+        @test entropy(ψ, site) ≈ Ss[site]
+        @test entropy(ψ, site) ≈ entropy(entanglement_spectrum(ψ, site))
+    end
+
+    # product state has zero entropy everywhere
+    ψ_product = InfiniteMPS([d, d], [oneunit(D), oneunit(D)])
+    Ss_product = entropy(ψ_product)
+    @test all(S -> isapprox(S, 0; atol = 1.0e-10), Ss_product)
+end

From 26bfb5acecf6f63e4a70b372e6b75274354aabc7 Mon Sep 17 00:00:00 2001
From: Akshay Shankar <sakshays.2000@gmail.com>
Date: Mon, 23 Feb 2026 17:58:58 +0100
Subject: [PATCH 04/14] Deep copying MPS with copy (#387)

* broadcast copy over arrays

* add basic tests for copying mps

* fix variable naming mismatch

* small fixes

* format

---------

Co-authored-by: Lukas Devos <ldevos98@gmail.com>
---
 test/states/infinitemps.jl | 25 +++++++++++++++++++++++++
 1 file changed, 25 insertions(+)

diff --git a/test/states/infinitemps.jl b/test/states/infinitemps.jl
index 7f2cc6b62..f0cc062dc 100644
--- a/test/states/infinitemps.jl
+++ b/test/states/infinitemps.jl
@@ -105,3 +105,28 @@ end
     Ss_product = entropy(ψ_product)
     @test all(S -> isapprox(S, 0; atol = 1.0e-10), Ss_product)
 end
+
+@testset "InfiniteMPS copying" begin
+    mps1 = InfiniteMPS(rand, ComplexF64, ℂ^2, ℂ^5)
+    mps2 = copy(mps1)
+
+    @test mps1 !== mps2
+
+    # elements are equal
+    @test mps1.AL[1] == mps2.AL[1]
+    @test mps1.AR[1] == mps2.AR[1]
+    @test mps1.AC[1] == mps2.AC[1]
+    @test mps1.C[1] == mps2.C[1]
+
+    # arrays are distinct
+    @test mps1.AL !== mps2.AL
+    @test mps1.AR !== mps2.AR
+    @test mps1.AC !== mps2.AC
+    @test mps1.C !== mps2.C
+
+    # tensors are distinct
+    @test mps1.AL[1] !== mps2.AL[1]
+    @test mps1.AR[1] !== mps2.AR[1]
+    @test mps1.AC[1] !== mps2.AC[1]
+    @test mps1.C[1] !== mps2.C[1]
+end

From 948505cfbc1e94271bee98098994f18433883009 Mon Sep 17 00:00:00 2001
From: Lukas Devos <ldevos98@gmail.com>
Date: Fri, 20 Feb 2026 14:02:50 -0500
Subject: [PATCH 05/14] fix wrong testcase

---
 test/operators/mpo.jl | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)

diff --git a/test/operators/mpo.jl b/test/operators/mpo.jl
index c73608c6d..cec8e0145 100644
--- a/test/operators/mpo.jl
+++ b/test/operators/mpo.jl
@@ -99,3 +99,26 @@ end
     @test OperatorStyle(typeof(H)) == MPOStyle()
     @test OperatorStyle(H) == MPOStyle()
 end
+
+@testset "Adapt" for V in (ℂ^2, U1Space(-1 => 1, 0 => 1, 1 => 1))
+    L = 3
+    o = rand(Float32, V^L ← V^L)
+    mpo1 = FiniteMPO(o)
+    for T in (Float64, ComplexF64)
+        mpo2 = @testinferred adapt(Vector{T}, mpo1)
+        @test mpo2 isa FiniteMPO
+        @test scalartype(mpo2) == T
+        @test storagetype(mpo2) == Vector{T}
+        @test convert(TensorMap, mpo2) ≈ o
+    end
+
+    mpo3 = InfiniteMPO(mpo1[2:2])
+    for T in (Float64, ComplexF64)
+        mpo4 = @testinferred adapt(Vector{T}, mpo3)
+        @test mpo4 isa InfiniteMPO
+        @test scalartype(mpo4) == T
+        @test storagetype(mpo4) == Vector{T}
+        @test dot(mpo3, mpo4) ≈ norm(mpo3)^2 atol = 1.0e-4
+    end
+
+end

From e00d5b86c128201a361879d890c6090a50d5026f Mon Sep 17 00:00:00 2001
From: Lukas Devos <ldevos98@gmail.com>
Date: Fri, 20 Feb 2026 15:46:57 -0500
Subject: [PATCH 06/14] alter JordanMPOTensor Adapt implementation

---
 ext/MPSKitAdaptExt.jl | 40 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 40 insertions(+)
 create mode 100644 ext/MPSKitAdaptExt.jl

diff --git a/ext/MPSKitAdaptExt.jl b/ext/MPSKitAdaptExt.jl
new file mode 100644
index 000000000..433a81b92
--- /dev/null
+++ b/ext/MPSKitAdaptExt.jl
@@ -0,0 +1,40 @@
+module MPSKitAdaptExt
+
+using TensorKit: space, spacetype
+using MPSKit
+using BlockTensorKit: nonzero_pairs
+using Adapt
+
+function Adapt.adapt_structure(to, mps::FiniteMPS)
+    ad = adapt(to)
+    adapt_not_missing(x) = ismissing(x) ? x : ad(x)
+
+    TA = Base.promote_op(ad, MPSKit.site_type(mps))
+    TB = Base.promote_op(ad, MPSKit.bond_type(mps))
+
+    ALs = map!(adapt_not_missing, similar(mps.ALs, Union{Missing, TA}), mps.ALs)
+    ARs = map!(adapt_not_missing, similar(mps.ARs, Union{Missing, TA}), mps.ARs)
+    ACs = map!(adapt_not_missing, similar(mps.ACs, Union{Missing, TA}), mps.ACs)
+    Cs = map!(adapt_not_missing, similar(mps.Cs, Union{Missing, TB}), mps.Cs)
+
+    return FiniteMPS{TA, TB}(ALs, ARs, ACs, Cs)
+end
+
+function Adapt.adapt_structure(to, mps::InfiniteMPS)
+    ad = adapt(to)
+    AL = map(ad, mps.AL)
+    AR = map(ad, mps.AR)
+    C = map(ad, mps.C)
+    AC = map(ad, mps.AC)
+
+    return InfiniteMPS{eltype(AL), eltype(C)}(AL, AR, C, AC)
+end
+
+Adapt.adapt_structure(to, mpo::MPO) = MPO(map(adapt(to), mpo.O))
+
+Adapt.adapt_structure(to, W::MPSKit.JordanMPOTensor) =
+    MPSKit.JordanMPOTensor(space(W), adapt(to, W.A), adapt(to, W.B), adapt(to, W.C), adapt(to, W.D))
+
+Adapt.adapt_structure(to, mpo::MPOHamiltonian) = MPOHamiltonian(map(adapt(to), mpo.W))
+
+end

From c942523e1d44bc8fa881fecb1155102ba20eae92 Mon Sep 17 00:00:00 2001
From: Lukas Devos <ldevos98@gmail.com>
Date: Fri, 20 Feb 2026 15:55:26 -0500
Subject: [PATCH 07/14] type stability chenanigans

---
 ext/MPSKitAdaptExt.jl | 11 +++++------
 1 file changed, 5 insertions(+), 6 deletions(-)

diff --git a/ext/MPSKitAdaptExt.jl b/ext/MPSKitAdaptExt.jl
index 433a81b92..4a85a285f 100644
--- a/ext/MPSKitAdaptExt.jl
+++ b/ext/MPSKitAdaptExt.jl
@@ -26,15 +26,14 @@ function Adapt.adapt_structure(to, mps::InfiniteMPS)
     AR = map(ad, mps.AR)
     C = map(ad, mps.C)
     AC = map(ad, mps.AC)
-
     return InfiniteMPS{eltype(AL), eltype(C)}(AL, AR, C, AC)
 end
 
-Adapt.adapt_structure(to, mpo::MPO) = MPO(map(adapt(to), mpo.O))
-
-Adapt.adapt_structure(to, W::MPSKit.JordanMPOTensor) =
+# inline to improve type stability with closures
+@inline Adapt.adapt_structure(to, mpo::MPO) = MPO(map(adapt(to), mpo.O))
+@inline Adapt.adapt_structure(to, W::MPSKit.JordanMPOTensor) =
     MPSKit.JordanMPOTensor(space(W), adapt(to, W.A), adapt(to, W.B), adapt(to, W.C), adapt(to, W.D))
-
-Adapt.adapt_structure(to, mpo::MPOHamiltonian) = MPOHamiltonian(map(adapt(to), mpo.W))
+@inline Adapt.adapt_structure(to, mpo::MPOHamiltonian) =
+    MPOHamiltonian(map(adapt(to), mpo.W))
 
 end

From 8c0bfa1d81c024664776d035f71344f7ccd898a6 Mon Sep 17 00:00:00 2001
From: Lukas Devos <ldevos98@gmail.com>
Date: Mon, 23 Feb 2026 15:20:20 -0500
Subject: [PATCH 08/14] bump TensorKit minimal version

---
 Project.toml | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/Project.toml b/Project.toml
index 0ba745a7f..ab58d0aa9 100644
--- a/Project.toml
+++ b/Project.toml
@@ -26,7 +26,7 @@ VectorInterface = "409d34a3-91d5-4945-b6ec-7529ddf182d8"
 [compat]
 Accessors = "0.1"
 Aqua = "0.8.9"
-BlockTensorKit = "0.3.4"
+BlockTensorKit = "0.3.8"
 Combinatorics = "1"
 Compat = "3.47, 4.10"
 DocStringExtensions = "0.9.3"
@@ -43,7 +43,7 @@ Plots = "1.40"
 Printf = "1"
 Random = "1"
 RecipesBase = "1.1"
-TensorKit = "0.16"
+TensorKit = "0.16.3"
 TensorKitManifolds = "0.7"
 TensorKitTensors = "0.2"
 TensorOperations = "5"

From c5f54b3e9c6b87640e99cc57b5d9632af4b43f6e Mon Sep 17 00:00:00 2001
From: Lukas Devos <ldevos98@gmail.com>
Date: Mon, 23 Feb 2026 17:53:59 -0500
Subject: [PATCH 09/14] more bypassing of type stability issues...

---
 ext/MPSKitAdaptExt.jl | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/ext/MPSKitAdaptExt.jl b/ext/MPSKitAdaptExt.jl
index 4a85a285f..6f0b0c7f2 100644
--- a/ext/MPSKitAdaptExt.jl
+++ b/ext/MPSKitAdaptExt.jl
@@ -34,6 +34,6 @@ end
 @inline Adapt.adapt_structure(to, W::MPSKit.JordanMPOTensor) =
     MPSKit.JordanMPOTensor(space(W), adapt(to, W.A), adapt(to, W.B), adapt(to, W.C), adapt(to, W.D))
 @inline Adapt.adapt_structure(to, mpo::MPOHamiltonian) =
-    MPOHamiltonian(map(adapt(to), mpo.W))
+    MPOHamiltonian(map(x -> adapt(to, x), mpo.W))
 
 end

From 2db608af103b341d0fa0fe027554c21af2b603cf Mon Sep 17 00:00:00 2001
From: Lukas Devos <ldevos98@gmail.com>
Date: Tue, 24 Feb 2026 09:38:21 -0500
Subject: [PATCH 10/14] fix some tests

---
 test/operators/mpo.jl            |  1 -
 test/operators/mpohamiltonian.jl | 34 +++++++++++++++++++++++++++++++-
 2 files changed, 33 insertions(+), 2 deletions(-)

diff --git a/test/operators/mpo.jl b/test/operators/mpo.jl
index cec8e0145..f93d4a9c2 100644
--- a/test/operators/mpo.jl
+++ b/test/operators/mpo.jl
@@ -120,5 +120,4 @@ end
         @test storagetype(mpo4) == Vector{T}
         @test dot(mpo3, mpo4) ≈ norm(mpo3)^2 atol = 1.0e-4
     end
-
 end
diff --git a/test/operators/mpohamiltonian.jl b/test/operators/mpohamiltonian.jl
index 9ff79f4c1..40e3690eb 100644
--- a/test/operators/mpohamiltonian.jl
+++ b/test/operators/mpohamiltonian.jl
@@ -4,8 +4,8 @@ println("
 ----------------------------
 ")
 
-using .TestSetup
 using Test, TestExtras
+using Adapt
 using MPSKit
 using MPSKit: GeometryStyle, FiniteChainStyle, InfiniteChainStyle, OperatorStyle, HamiltonianStyle
 using TensorKit
@@ -240,3 +240,35 @@ end
     h4 = H4 * H4
     @test real(expectation_value(ψ2, H4)) >= 0
 end
+
+@testset "Adapt" for V in (ℂ^2, U1Space(-1 => 1, 0 => 1, 1 => 1))
+    h = rand(Float32, V^2 ← V^2)
+    h += h'
+
+    L = 4
+    H1 = FiniteMPOHamiltonian(
+        fill(V, L),
+        ((i, i + 1) => h for i in 1:(L - 1))...,
+        ((i, i + 2) => h for i in 1:(L - 2))...,
+        ((i, i + 3) => h for i in 1:(L - 3))...,
+    )
+    mps1 = FiniteMPS(physicalspace(H1), oneunit(V))
+
+    for T in (Float64, ComplexF64)
+        H2 = @testinferred adapt(Vector{T}, H1)
+        @test H2 isa FiniteMPOHamiltonian
+        @test scalartype(H2) == T
+        @test storagetype(H2) == Vector{T}
+        @test expectation_value(mps1, H1) ≈ expectation_value(mps1, H2)
+    end
+
+    H3 = InfiniteMPOHamiltonian(fill(V, L), (1, 2) => h, (1, 3) => h, (1, 4) => h)
+    mps2 = InfiniteMPS(physicalspace(H3), [oneunit(V)])
+    for T in (Float64, ComplexF64)
+        H4 = @testinferred adapt(Vector{T}, H3)
+        @test H4 isa InfiniteMPOHamiltonian
+        @test scalartype(H4) == T
+        @test storagetype(H4) == Vector{T}
+        @test expectation_value(mps2, H3) ≈ expectation_value(mps2, H4)
+    end
+end

From d97fc72ec9a64ea2d572e1503c20f14be90e2d8a Mon Sep 17 00:00:00 2001
From: Lukas Devos <ldevos98@gmail.com>
Date: Tue, 24 Feb 2026 09:54:28 -0500
Subject: [PATCH 11/14] lost of git struggles

---
 Project.toml | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/Project.toml b/Project.toml
index ab58d0aa9..e36c838f5 100644
--- a/Project.toml
+++ b/Project.toml
@@ -23,8 +23,15 @@ TensorKitManifolds = "11fa318c-39cb-4a83-b1ed-cdc7ba1e3684"
 TensorOperations = "6aa20fa7-93e2-5fca-9bc0-fbd0db3c71a2"
 VectorInterface = "409d34a3-91d5-4945-b6ec-7529ddf182d8"
 
+[weakdeps]
+Adapt = "79e6a3ab-5dfb-504d-930d-738a2a938a0e"
+
+[extensions]
+MPSKitAdaptExt = "Adapt"
+
 [compat]
 Accessors = "0.1"
+Adapt = "4"
 Aqua = "0.8.9"
 BlockTensorKit = "0.3.8"
 Combinatorics = "1"
@@ -53,6 +60,7 @@ VectorInterface = "0.2, 0.3, 0.4, 0.5"
 julia = "1.10"
 
 [extras]
+Adapt = "79e6a3ab-5dfb-504d-930d-738a2a938a0e"
 Aqua = "4c88cf16-eb10-579e-8560-4a9242c79595"
 Combinatorics = "861a8166-3701-5b0c-9a16-15d98fcdc6aa"
 ParallelTestRunner = "d3525ed8-44d0-4b2c-a655-542cee43accc"
@@ -63,4 +71,4 @@ Test = "8dfed614-e22c-5e08-85e1-65c5234f0b40"
 TestExtras = "5ed8adda-3752-4e41-b88a-e8b09835ee3a"
 
 [targets]
-test = ["Aqua", "Pkg", "Test", "TestExtras", "Plots", "Combinatorics", "ParallelTestRunner", "TensorKitTensors"]
+test = ["Aqua", "Adapt", "Pkg", "Test", "TestExtras", "Plots", "Combinatorics", "ParallelTestRunner", "TensorKitTensors"]

From df834d2ca7b3974d46f51efefc5a1fc75ab83b4b Mon Sep 17 00:00:00 2001
From: Lukas Devos <ldevos98@gmail.com>
Date: Tue, 24 Feb 2026 11:39:08 -0500
Subject: [PATCH 12/14] more git misery!

---
 Project.toml | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/Project.toml b/Project.toml
index ab58d0aa9..e36c838f5 100644
--- a/Project.toml
+++ b/Project.toml
@@ -23,8 +23,15 @@ TensorKitManifolds = "11fa318c-39cb-4a83-b1ed-cdc7ba1e3684"
 TensorOperations = "6aa20fa7-93e2-5fca-9bc0-fbd0db3c71a2"
 VectorInterface = "409d34a3-91d5-4945-b6ec-7529ddf182d8"
 
+[weakdeps]
+Adapt = "79e6a3ab-5dfb-504d-930d-738a2a938a0e"
+
+[extensions]
+MPSKitAdaptExt = "Adapt"
+
 [compat]
 Accessors = "0.1"
+Adapt = "4"
 Aqua = "0.8.9"
 BlockTensorKit = "0.3.8"
 Combinatorics = "1"
@@ -53,6 +60,7 @@ VectorInterface = "0.2, 0.3, 0.4, 0.5"
 julia = "1.10"
 
 [extras]
+Adapt = "79e6a3ab-5dfb-504d-930d-738a2a938a0e"
 Aqua = "4c88cf16-eb10-579e-8560-4a9242c79595"
 Combinatorics = "861a8166-3701-5b0c-9a16-15d98fcdc6aa"
 ParallelTestRunner = "d3525ed8-44d0-4b2c-a655-542cee43accc"
@@ -63,4 +71,4 @@ Test = "8dfed614-e22c-5e08-85e1-65c5234f0b40"
 TestExtras = "5ed8adda-3752-4e41-b88a-e8b09835ee3a"
 
 [targets]
-test = ["Aqua", "Pkg", "Test", "TestExtras", "Plots", "Combinatorics", "ParallelTestRunner", "TensorKitTensors"]
+test = ["Aqua", "Adapt", "Pkg", "Test", "TestExtras", "Plots", "Combinatorics", "ParallelTestRunner", "TensorKitTensors"]

From c30fc3e9160e6a50f17c0c71a6862fee069c4bed Mon Sep 17 00:00:00 2001
From: Lukas Devos <ldevos98@gmail.com>
Date: Tue, 24 Feb 2026 12:03:12 -0500
Subject: [PATCH 13/14] handle storagetype better

---
 src/states/abstractmps.jl | 2 ++
 src/states/finitemps.jl   | 3 ---
 2 files changed, 2 insertions(+), 3 deletions(-)

diff --git a/src/states/abstractmps.jl b/src/states/abstractmps.jl
index 3d277aff4..e442100db 100644
--- a/src/states/abstractmps.jl
+++ b/src/states/abstractmps.jl
@@ -200,6 +200,8 @@ TensorKit.spacetype(ψtype::Type{<:AbstractMPS}) = spacetype(site_type(ψtype))
 TensorKit.sectortype(ψ::AbstractMPS) = sectortype(typeof(ψ))
 TensorKit.sectortype(ψtype::Type{<:AbstractMPS}) = sectortype(site_type(ψtype))
 
+TensorKit.storagetype(ψtype::Type{<:AbstractMPS}) = storagetype(site_type(ψtype))
+
 """
     left_virtualspace(ψ::AbstractMPS, [pos=1:length(ψ)])
     
diff --git a/src/states/finitemps.jl b/src/states/finitemps.jl
index c956b9730..5bfdcba92 100644
--- a/src/states/finitemps.jl
+++ b/src/states/finitemps.jl
@@ -387,9 +387,6 @@ end
 
 site_type(::Type{<:FiniteMPS{A}}) where {A} = A
 bond_type(::Type{<:FiniteMPS{<:Any, B}}) where {B} = B
-function TensorKit.storagetype(::Union{MPS, Type{MPS}}) where {A, MPS <: FiniteMPS{A}}
-    return storagetype(A)
-end
 
 function left_virtualspace(ψ::FiniteMPS, n::Integer)
     checkbounds(ψ, n)

From 8682063879e3ad6f32088a10458c78a5f1738164 Mon Sep 17 00:00:00 2001
From: Lukas Devos <ldevos98@gmail.com>
Date: Tue, 24 Feb 2026 15:15:55 -0500
Subject: [PATCH 14/14] disable lts type stability tests

---
 test/operators/mpohamiltonian.jl | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/test/operators/mpohamiltonian.jl b/test/operators/mpohamiltonian.jl
index fe1c5858c..e199df30f 100644
--- a/test/operators/mpohamiltonian.jl
+++ b/test/operators/mpohamiltonian.jl
@@ -255,7 +255,11 @@ end
     mps1 = FiniteMPS(physicalspace(H1), oneunit(V))
 
     for T in (Float64, ComplexF64)
-        H2 = @testinferred adapt(Vector{T}, H1)
+        H2 = if VERSION <= v"1.12"
+            adapt(Vector{T}, H1)
+        else
+            @testinferred adapt(Vector{T}, H1)
+        end
         @test H2 isa FiniteMPOHamiltonian
         @test scalartype(H2) == T
         @test storagetype(H2) == Vector{T}
@@ -265,7 +269,12 @@ end
     H3 = InfiniteMPOHamiltonian(fill(V, L), (1, 2) => h, (1, 3) => h, (1, 4) => h)
     mps2 = InfiniteMPS(physicalspace(H3), [oneunit(V)])
     for T in (Float64, ComplexF64)
-        H4 = @testinferred adapt(Vector{T}, H3)
+        H4 = if VERSION <= v"1.12"
+            # this is type unstable for LTS for some reason
+            adapt(Vector{T}, H3)
+        else
+            @testinferred adapt(Vector{T}, H3)
+        end
         @test H4 isa InfiniteMPOHamiltonian
         @test scalartype(H4) == T
         @test storagetype(H4) == Vector{T}