diff --git a/src/libcmd/common-eval-args.cc b/src/libcmd/common-eval-args.cc
index 8b9f49266..00b09f4ea 100644
--- a/src/libcmd/common-eval-args.cc
+++ b/src/libcmd/common-eval-args.cc
@@ -168,9 +168,9 @@ Bindings * MixEvalArgs::getAutoArgs(EvalState & state)
                                 ? state.rootPath(absPath(getCommandBaseDir()))
                                 : state.rootPath(".")));
                 },
-                [&](const AutoArgString & arg) { v->mkString(arg.s); },
-                [&](const AutoArgFile & arg) { v->mkString(readFile(arg.path.string())); },
-                [&](const AutoArgStdin & arg) { v->mkString(readFile(STDIN_FILENO)); }},
+                [&](const AutoArgString & arg) { v->mkString(arg.s, state.mem); },
+                [&](const AutoArgFile & arg) { v->mkString(readFile(arg.path.string()), state.mem); },
+                [&](const AutoArgStdin & arg) { v->mkString(readFile(STDIN_FILENO), state.mem); }},
             arg);
         res.insert(state.symbols.create(name), v);
     }
diff --git a/src/libexpr-c/nix_api_expr.cc b/src/libexpr-c/nix_api_expr.cc
index 76f3b6486..0dd9fa0a5 100644
--- a/src/libexpr-c/nix_api_expr.cc
+++ b/src/libexpr-c/nix_api_expr.cc
@@ -69,8 +69,8 @@ nix_err nix_expr_eval_from_string(
         context->last_err_code = NIX_OK;
     try {
         nix::Expr * parsedExpr = state->state.parseExprFromString(expr, state->state.rootPath(nix::CanonPath(path)));
-        state->state.eval(parsedExpr, value->value);
-        state->state.forceValue(value->value, nix::noPos);
+        state->state.eval(parsedExpr, *value->value);
+        state->state.forceValue(*value->value, nix::noPos);
     }
     NIXC_CATCH_ERRS
 }
@@ -80,8 +80,8 @@ nix_err nix_value_call(nix_c_context * context, EvalState * state, Value * fn, n
     if (context)
         context->last_err_code = NIX_OK;
     try {
-        state->state.callFunction(fn->value, arg->value, value->value, nix::noPos);
-        state->state.forceValue(value->value, nix::noPos);
+        state->state.callFunction(*fn->value, *arg->value, *value->value, nix::noPos);
+        state->state.forceValue(*value->value, nix::noPos);
     }
     NIXC_CATCH_ERRS
 }
@@ -91,9 +91,15 @@ nix_err nix_value_call_multi(
 {
     if (context)
         context->last_err_code = NIX_OK;
+
+    std::vector<nix::Value *> internal_args;
+    internal_args.reserve(nargs);
+    for (size_t i = 0; i < nargs; i++)
+        internal_args.push_back(args[i]->value);
+
     try {
-        state->state.callFunction(fn->value, {(nix::Value **) args, nargs}, value->value, nix::noPos);
-        state->state.forceValue(value->value, nix::noPos);
+        state->state.callFunction(*fn->value, {internal_args.data(), nargs}, *value->value, nix::noPos);
+        state->state.forceValue(*value->value, nix::noPos);
     }
     NIXC_CATCH_ERRS
 }
@@ -103,7 +109,7 @@ nix_err nix_value_force(nix_c_context * context, EvalState * state, nix_value *
     if (context)
         context->last_err_code = NIX_OK;
     try {
-        state->state.forceValue(value->value, nix::noPos);
+        state->state.forceValue(*value->value, nix::noPos);
     }
     NIXC_CATCH_ERRS
 }
@@ -113,7 +119,7 @@ nix_err nix_value_force_deep(nix_c_context * context, EvalState * state, nix_val
     if (context)
         context->last_err_code = NIX_OK;
     try {
-        state->state.forceValueDeep(value->value);
+        state->state.forceValueDeep(*value->value);
     }
     NIXC_CATCH_ERRS
 }
diff --git a/src/libexpr-c/nix_api_expr_internal.h b/src/libexpr-c/nix_api_expr_internal.h
index 3aa1d9932..07c7a2194 100644
--- a/src/libexpr-c/nix_api_expr_internal.h
+++ b/src/libexpr-c/nix_api_expr_internal.h
@@ -39,7 +39,13 @@ struct ListBuilder
 
 struct nix_value
 {
-    nix::Value value;
+    nix::Value * value;
+    /**
+     * As we move to a managed heap, we need EvalMemory in more places. Ideally, we would take in EvalState or
+     * EvalMemory as an argument when we need it, but we don't want to make changes to the stable C api, so we stuff it
+     * into the nix_value that will get passed in to the relevant functions.
+     */
+    nix::EvalMemory * mem;
 };
 
 struct nix_string_return
diff --git a/src/libexpr-c/nix_api_value.cc b/src/libexpr-c/nix_api_value.cc
index e231c36f4..be8ff4926 100644
--- a/src/libexpr-c/nix_api_value.cc
+++ b/src/libexpr-c/nix_api_value.cc
@@ -20,7 +20,7 @@ static const nix::Value & check_value_not_null(const nix_value * value)
     if (!value) {
         throw std::runtime_error("nix_value is null");
     }
-    return *((const nix::Value *) value);
+    return *value->value;
 }
 
 static nix::Value & check_value_not_null(nix_value * value)
@@ -28,7 +28,7 @@ static nix::Value & check_value_not_null(nix_value * value)
     if (!value) {
         throw std::runtime_error("nix_value is null");
     }
-    return value->value;
+    return *value->value;
 }
 
 static const nix::Value & check_value_in(const nix_value * value)
@@ -58,9 +58,14 @@ static nix::Value & check_value_out(nix_value * value)
     return v;
 }
 
-static inline nix_value * as_nix_value_ptr(nix::Value * v)
+static inline nix_value * new_nix_value(nix::Value * v, nix::EvalMemory & mem)
 {
-    return reinterpret_cast<nix_value *>(v);
+    nix_value * ret = new (mem.allocBytes(sizeof(nix_value))) nix_value{
+        .value = v,
+        .mem = &mem,
+    };
+    nix_gc_incref(nullptr, ret);
+    return ret;
 }
 
 /**
@@ -69,7 +74,13 @@ static inline nix_value * as_nix_value_ptr(nix::Value * v)
  * Deals with errors and converts arguments from C++ into C types.
  */
 static void nix_c_primop_wrapper(
-    PrimOpFun f, void * userdata, nix::EvalState & state, const nix::PosIdx pos, nix::Value ** args, nix::Value & v)
+    PrimOpFun f,
+    void * userdata,
+    int arity,
+    nix::EvalState & state,
+    const nix::PosIdx pos,
+    nix::Value ** args,
+    nix::Value & v)
 {
     nix_c_context ctx;
 
@@ -85,8 +96,15 @@ static void nix_c_primop_wrapper(
     // ok because we don't see a need for this yet (e.g. inspecting thunks,
     // or maybe something to make blackholes work better; we don't know).
     nix::Value vTmp;
+    nix_value * vTmpPtr = new_nix_value(&vTmp, state.mem);
 
-    f(userdata, &ctx, (EvalState *) &state, (nix_value **) args, (nix_value *) &vTmp);
+    std::vector<nix_value *> external_args;
+    external_args.reserve(arity);
+    for (int i = 0; i < arity; i++) {
+        nix_value * external_arg = new_nix_value(args[i], state.mem);
+        external_args.push_back(external_arg);
+    }
+    f(userdata, &ctx, (EvalState *) &state, external_args.data(), vTmpPtr);
 
     if (ctx.last_err_code != NIX_OK) {
         /* TODO: Throw different errors depending on the error code */
@@ -135,7 +153,7 @@ PrimOp * nix_alloc_primop(
                     .args = {},
                     .arity = (size_t) arity,
                     .doc = doc,
-                    .fun = std::bind(nix_c_primop_wrapper, fun, user_data, _1, _2, _3, _4)};
+                    .fun = std::bind(nix_c_primop_wrapper, fun, user_data, arity, _1, _2, _3, _4)};
         if (args)
             for (size_t i = 0; args[i]; i++)
                 p->args.emplace_back(*args);
@@ -160,8 +178,7 @@ nix_value * nix_alloc_value(nix_c_context * context, EvalState * state)
     if (context)
         context->last_err_code = NIX_OK;
     try {
-        nix_value * res = as_nix_value_ptr(state->state.allocValue());
-        nix_gc_incref(nullptr, res);
+        nix_value * res = new_nix_value(state->state.allocValue(), state->state.mem);
         return res;
     }
     NIXC_CATCH_ERRS_NULL
@@ -331,10 +348,10 @@ nix_value * nix_get_list_byidx(nix_c_context * context, const nix_value * value,
             return nullptr;
         }
         auto * p = v.listView()[ix];
-        nix_gc_incref(nullptr, p);
-        if (p != nullptr)
-            state->state.forceValue(*p, nix::noPos);
-        return as_nix_value_ptr(p);
+        if (p == nullptr)
+            return nullptr;
+        state->state.forceValue(*p, nix::noPos);
+        return new_nix_value(p, state->state.mem);
     }
     NIXC_CATCH_ERRS_NULL
 }
@@ -352,9 +369,8 @@ nix_get_list_byidx_lazy(nix_c_context * context, const nix_value * value, EvalSt
             return nullptr;
         }
         auto * p = v.listView()[ix];
-        nix_gc_incref(nullptr, p);
         // Note: intentionally NOT calling forceValue() to keep the element lazy
-        return as_nix_value_ptr(p);
+        return new_nix_value(p, state->state.mem);
     }
     NIXC_CATCH_ERRS_NULL
 }
@@ -369,9 +385,8 @@ nix_value * nix_get_attr_byname(nix_c_context * context, const nix_value * value
         nix::Symbol s = state->state.symbols.create(name);
         auto attr = v.attrs()->get(s);
         if (attr) {
-            nix_gc_incref(nullptr, attr->value);
             state->state.forceValue(*attr->value, nix::noPos);
-            return as_nix_value_ptr(attr->value);
+            return new_nix_value(attr->value, state->state.mem);
         }
         nix_set_err_msg(context, NIX_ERR_KEY, "missing attribute");
         return nullptr;
@@ -390,9 +405,8 @@ nix_get_attr_byname_lazy(nix_c_context * context, const nix_value * value, EvalS
         nix::Symbol s = state->state.symbols.create(name);
         auto attr = v.attrs()->get(s);
         if (attr) {
-            nix_gc_incref(nullptr, attr->value);
             // Note: intentionally NOT calling forceValue() to keep the attribute lazy
-            return as_nix_value_ptr(attr->value);
+            return new_nix_value(attr->value, state->state.mem);
         }
         nix_set_err_msg(context, NIX_ERR_KEY, "missing attribute");
         return nullptr;
@@ -440,9 +454,8 @@ nix_get_attr_byidx(nix_c_context * context, nix_value * value, EvalState * state
         }
         const nix::Attr & a = (*v.attrs())[i];
         *name = state->state.symbols[a.name].c_str();
-        nix_gc_incref(nullptr, a.value);
         state->state.forceValue(*a.value, nix::noPos);
-        return as_nix_value_ptr(a.value);
+        return new_nix_value(a.value, state->state.mem);
     }
     NIXC_CATCH_ERRS_NULL
 }
@@ -461,9 +474,8 @@ nix_value * nix_get_attr_byidx_lazy(
         }
         const nix::Attr & a = (*v.attrs())[i];
         *name = state->state.symbols[a.name].c_str();
-        nix_gc_incref(nullptr, a.value);
         // Note: intentionally NOT calling forceValue() to keep the attribute lazy
-        return as_nix_value_ptr(a.value);
+        return new_nix_value(a.value, state->state.mem);
     }
     NIXC_CATCH_ERRS_NULL
 }
@@ -503,7 +515,7 @@ nix_err nix_init_string(nix_c_context * context, nix_value * value, const char *
         context->last_err_code = NIX_OK;
     try {
         auto & v = check_value_out(value);
-        v.mkString(std::string_view(str));
+        v.mkString(std::string_view(str), *value->mem);
     }
     NIXC_CATCH_ERRS
 }
@@ -514,7 +526,7 @@ nix_err nix_init_path_string(nix_c_context * context, EvalState * s, nix_value *
         context->last_err_code = NIX_OK;
     try {
         auto & v = check_value_out(value);
-        v.mkPath(s->state.rootPath(nix::CanonPath(str)));
+        v.mkPath(s->state.rootPath(nix::CanonPath(str)), s->state.mem);
     }
     NIXC_CATCH_ERRS
 }
diff --git a/src/libexpr-tests/json.cc b/src/libexpr-tests/json.cc
index aa71c4d86..31e7a18c5 100644
--- a/src/libexpr-tests/json.cc
+++ b/src/libexpr-tests/json.cc
@@ -73,7 +73,7 @@ TEST_F(JSONValueTest, StringQuotes)
 TEST_F(JSONValueTest, DISABLED_Path)
 {
     Value v;
-    v.mkPath(state.rootPath(CanonPath("/test")));
+    v.mkPath(state.rootPath(CanonPath("/test")), state.mem);
     ASSERT_EQ(getJSONValue(v), "\"/nix/store/g1w7hy3qg1w7hy3qg1w7hy3qg1w7hy3q-x\"");
 }
 } /* namespace nix */
diff --git a/src/libexpr-tests/value/print.cc b/src/libexpr-tests/value/print.cc
index 0456835b4..d22606219 100644
--- a/src/libexpr-tests/value/print.cc
+++ b/src/libexpr-tests/value/print.cc
@@ -268,7 +268,7 @@ struct StringPrintingTests : LibExprTest
     void test(std::string_view literal, std::string_view expected, unsigned int maxLength, A... args)
     {
         Value v;
-        v.mkString(literal);
+        v.mkString(literal, state.mem);
 
         std::stringstream out;
         printValue(state, out, v, PrintOptions{.maxStringLength = maxLength});
@@ -353,7 +353,7 @@ TEST_F(ValuePrintingTests, ansiColorsStringElided)
 TEST_F(ValuePrintingTests, ansiColorsPath)
 {
     Value v;
-    v.mkPath(state.rootPath(CanonPath("puppy")));
+    v.mkPath(state.rootPath(CanonPath("puppy")), state.mem);
 
     test(v, ANSI_GREEN "/puppy" ANSI_NORMAL, PrintOptions{.ansiColors = true});
 }
diff --git a/src/libexpr/eval.cc b/src/libexpr/eval.cc
index 29aa11035..71834f10f 100644
--- a/src/libexpr/eval.cc
+++ b/src/libexpr/eval.cc
@@ -81,20 +81,20 @@ static const char * makeImmutableString(std::string_view s)
     return t;
 }
 
-StringData & StringData::alloc(size_t size)
+StringData & StringData::alloc(EvalMemory & mem, size_t size)
 {
-    void * t = GC_MALLOC_ATOMIC(sizeof(StringData) + size + 1);
+    void * t = mem.allocBytes(sizeof(StringData) + size + 1);
     if (!t)
         throw std::bad_alloc();
     auto res = new (t) StringData(size);
     return *res;
 }
 
-const StringData & StringData::make(std::string_view s)
+const StringData & StringData::make(EvalMemory & mem, std::string_view s)
 {
     if (s.empty())
         return ""_sds;
-    auto & res = alloc(s.size());
+    auto & res = alloc(mem, s.size());
     std::memcpy(&res.data_, s.data(), s.size());
     res.data_[s.size()] = '\0';
     return res;
@@ -849,9 +849,9 @@ DebugTraceStacker::DebugTraceStacker(EvalState & evalState, DebugTrace t)
         evalState.runDebugRepl(nullptr, trace.env, trace.expr);
 }
 
-void Value::mkString(std::string_view s)
+void Value::mkString(std::string_view s, EvalMemory & mem)
 {
-    mkStringNoCopy(StringData::make(s));
+    mkStringNoCopy(StringData::make(mem, s));
 }
 
 Value::StringWithContext::Context *
@@ -862,13 +862,13 @@ Value::StringWithContext::Context::fromBuilder(const NixStringContext & context,
 
     auto ctx = new (mem.allocBytes(sizeof(Context) + context.size() * sizeof(value_type))) Context(context.size());
     std::ranges::transform(
-        context, ctx->elems, [](const NixStringContextElem & elt) { return &StringData::make(elt.to_string()); });
+        context, ctx->elems, [&](const NixStringContextElem & elt) { return &StringData::make(mem, elt.to_string()); });
     return ctx;
 }
 
 void Value::mkString(std::string_view s, const NixStringContext & context, EvalMemory & mem)
 {
-    mkStringNoCopy(StringData::make(s), Value::StringWithContext::Context::fromBuilder(context, mem));
+    mkStringNoCopy(StringData::make(mem, s), Value::StringWithContext::Context::fromBuilder(context, mem));
 }
 
 void Value::mkStringMove(const StringData & s, const NixStringContext & context, EvalMemory & mem)
@@ -876,9 +876,9 @@ void Value::mkStringMove(const StringData & s, const NixStringContext & context,
     mkStringNoCopy(s, Value::StringWithContext::Context::fromBuilder(context, mem));
 }
 
-void Value::mkPath(const SourcePath & path)
+void Value::mkPath(const SourcePath & path, EvalMemory & mem)
 {
-    mkPath(&*path.accessor, StringData::make(path.path.abs()));
+    mkPath(&*path.accessor, StringData::make(mem, path.path.abs()));
 }
 
 inline Value * EvalState::lookupVar(Env * env, const ExprVar & var, bool noEval)
@@ -943,7 +943,7 @@ void EvalState::mkPos(Value & v, PosIdx p)
     auto origin = positions.originOf(p);
     if (auto path = std::get_if<SourcePath>(&origin)) {
         auto attrs = buildBindings(3);
-        attrs.alloc(s.file).mkString(path->path.abs());
+        attrs.alloc(s.file).mkString(path->path.abs(), mem);
         makePositionThunks(*this, p, attrs.alloc(s.line), attrs.alloc(s.column));
         v.mkAttrs(attrs);
     } else
@@ -2139,9 +2139,9 @@ void ExprConcatStrings::eval(EvalState & state, Env & env, Value & v)
         for (const auto & part : strings) {
             resultStr += *part;
         }
-        v.mkPath(state.rootPath(CanonPath(resultStr)));
+        v.mkPath(state.rootPath(CanonPath(resultStr)), state.mem);
     } else {
-        auto & resultStr = StringData::alloc(sSize);
+        auto & resultStr = StringData::alloc(state.mem, sSize);
         auto * tmp = resultStr.data();
         for (const auto & part : strings) {
             std::memcpy(tmp, part->data(), part->size());
diff --git a/src/libexpr/include/nix/expr/value.hh b/src/libexpr/include/nix/expr/value.hh
index ff62092f2..004dcc43f 100644
--- a/src/libexpr/include/nix/expr/value.hh
+++ b/src/libexpr/include/nix/expr/value.hh
@@ -232,13 +232,13 @@ public:
      * Allocate StringData on the (possibly) GC-managed heap and copy
      * the contents of s to it.
      */
-    static const StringData & make(std::string_view s);
+    static const StringData & make(EvalMemory & mem, std::string_view s);
 
     /**
      * Allocate StringData on the (possibly) GC-managed heap.
      * @param size Length of the string (without the NUL terminator).
      */
-    static StringData & alloc(size_t size);
+    static StringData & alloc(EvalMemory & mem, size_t size);
 
     size_t size() const
     {
@@ -1147,13 +1147,13 @@ public:
         setStorage(StringWithContext{.str = &s, .context = context});
     }
 
-    void mkString(std::string_view s);
+    void mkString(std::string_view s, EvalMemory & mem);
 
     void mkString(std::string_view s, const NixStringContext & context, EvalMemory & mem);
 
     void mkStringMove(const StringData & s, const NixStringContext & context, EvalMemory & mem);
 
-    void mkPath(const SourcePath & path);
+    void mkPath(const SourcePath & path, EvalMemory & mem);
 
     inline void mkPath(SourceAccessor * accessor, const StringData & path) noexcept
     {
diff --git a/src/libexpr/json-to-value.cc b/src/libexpr/json-to-value.cc
index 9c645e7fd..4a68308c6 100644
--- a/src/libexpr/json-to-value.cc
+++ b/src/libexpr/json-to-value.cc
@@ -151,7 +151,7 @@ public:
     bool string(string_t & val) override
     {
         forceNoNullByte(val);
-        rs->value(state).mkString(val);
+        rs->value(state).mkString(val, state.mem);
         rs->add();
         return true;
     }
diff --git a/src/libexpr/primops.cc b/src/libexpr/primops.cc
index 35f16a68d..573dee74f 100644
--- a/src/libexpr/primops.cc
+++ b/src/libexpr/primops.cc
@@ -53,7 +53,7 @@ RegisterPrimOp::PrimOps & RegisterPrimOp::primOps()
 static inline Value * mkString(EvalState & state, const std::csub_match & match)
 {
     Value * v = state.allocValue();
-    v->mkString({match.first, match.second});
+    v->mkString({match.first, match.second}, state.mem);
     return v;
 }
 
@@ -230,12 +230,12 @@ void derivationToValue(
                 NixStringContextElem::DrvDeep{.drvPath = storePath},
             },
             state.mem);
-    attrs.alloc(state.s.name).mkString(drv.env["name"]);
+    attrs.alloc(state.s.name).mkString(drv.env["name"], state.mem);
 
     auto list = state.buildList(drv.outputs.size());
     for (const auto & [i, o] : enumerate(drv.outputs)) {
         mkOutputString(state, attrs, storePath, o);
-        (list[i] = state.allocValue())->mkString(o.first);
+        (list[i] = state.allocValue())->mkString(o.first, state.mem);
     }
     attrs.alloc(state.s.outputs).mkList(list);
 
@@ -519,7 +519,7 @@ static void prim_typeOf(EvalState & state, const PosIdx pos, Value ** args, Valu
         v.mkStringNoCopy("lambda"_sds);
         break;
     case nExternal:
-        v.mkString(args[0]->external()->typeOf());
+        v.mkString(args[0]->external()->typeOf(), state.mem);
         break;
     case nFloat:
         v.mkStringNoCopy("float"_sds);
@@ -1176,7 +1176,7 @@ static void prim_getEnv(EvalState & state, const PosIdx pos, Value ** args, Valu
 {
     std::string name(
         state.forceStringNoCtx(*args[0], pos, "while evaluating the first argument passed to builtins.getEnv"));
-    v.mkString(state.settings.restrictEval || state.settings.pureEval ? "" : getEnv(name).value_or(""));
+    v.mkString(state.settings.restrictEval || state.settings.pureEval ? "" : getEnv(name).value_or(""), state.mem);
 }
 
 static RegisterPrimOp primop_getEnv({
@@ -1842,8 +1842,10 @@ static RegisterPrimOp primop_derivationStrict(
    ‘out’. */
 static void prim_placeholder(EvalState & state, const PosIdx pos, Value ** args, Value & v)
 {
-    v.mkString(hashPlaceholder(
-        state.forceStringNoCtx(*args[0], pos, "while evaluating the first argument passed to builtins.placeholder")));
+    v.mkString(
+        hashPlaceholder(state.forceStringNoCtx(
+            *args[0], pos, "while evaluating the first argument passed to builtins.placeholder")),
+        state.mem);
 }
 
 static RegisterPrimOp primop_placeholder({
@@ -2027,7 +2029,7 @@ static void prim_dirOf(EvalState & state, const PosIdx pos, Value ** args, Value
     state.forceValue(*args[0], pos);
     if (args[0]->type() == nPath) {
         auto path = args[0]->path();
-        v.mkPath(path.path.isRoot() ? path : path.parent());
+        v.mkPath(path.path.isRoot() ? path : path.parent(), state.mem);
     } else {
         NixStringContext context;
         auto path = state.coerceToString(
@@ -2144,7 +2146,7 @@ static void prim_findFile(EvalState & state, const PosIdx pos, Value ** args, Va
     auto path =
         state.forceStringNoCtx(*args[1], pos, "while evaluating the second argument passed to builtins.findFile");
 
-    v.mkPath(state.findFile(lookupPath, path, pos));
+    v.mkPath(state.findFile(lookupPath, path, pos), state.mem);
 }
 
 static RegisterPrimOp primop_findFile(
@@ -2293,7 +2295,7 @@ static void prim_hashFile(EvalState & state, const PosIdx pos, Value ** args, Va
 
     auto path = realisePath(state, pos, *args[1]);
 
-    v.mkString(hashString(*ha, path.readFile()).to_string(HashFormat::Base16, false));
+    v.mkString(hashString(*ha, path.readFile()).to_string(HashFormat::Base16, false), state.mem);
 }
 
 static RegisterPrimOp primop_hashFile({
@@ -2382,7 +2384,7 @@ static void prim_readDir(EvalState & state, const PosIdx pos, Value ** args, Val
             // detailed node info quickly in this case we produce a thunk to
             // query the file type lazily.
             auto epath = state.allocValue();
-            epath->mkPath(path / name);
+            epath->mkPath(path / name, state.mem);
             if (!readFileType)
                 readFileType = &state.getBuiltin("readFileType");
             attr.mkApp(readFileType, epath);
@@ -2763,7 +2765,7 @@ bool EvalState::callPathFilter(Value * filterFun, const SourcePath & path, PosId
     /* Call the filter function.  The first argument is the path, the
        second is a string indicating the type of the file. */
     Value arg1;
-    arg1.mkString(path.path.abs());
+    arg1.mkString(path.path.abs(), mem);
 
     // assert that type is not "unknown"
     Value * args[]{&arg1, const_cast<Value *>(&fileTypeToString(*this, st.type))};
@@ -4541,7 +4543,7 @@ static void prim_hashString(EvalState & state, const PosIdx pos, Value ** args,
     auto s =
         state.forceString(*args[1], context, pos, "while evaluating the second argument passed to builtins.hashString");
 
-    v.mkString(hashString(*ha, s).to_string(HashFormat::Base16, false));
+    v.mkString(hashString(*ha, s).to_string(HashFormat::Base16, false), state.mem);
 }
 
 static RegisterPrimOp primop_hashString({
@@ -4574,7 +4576,7 @@ static void prim_convertHash(EvalState & state, const PosIdx pos, Value ** args,
     HashFormat hf = parseHashFormat(
         state.forceStringNoCtx(*iteratorToHashFormat->value, pos, "while evaluating the attribute 'toHashFormat'"));
 
-    v.mkString(Hash::parseAny(hash, ha).to_string(hf, hf == HashFormat::SRI));
+    v.mkString(Hash::parseAny(hash, ha).to_string(hf, hf == HashFormat::SRI), state.mem);
 }
 
 static RegisterPrimOp primop_convertHash({
@@ -4992,8 +4994,8 @@ static void prim_parseDrvName(EvalState & state, const PosIdx pos, Value ** args
         state.forceStringNoCtx(*args[0], pos, "while evaluating the first argument passed to builtins.parseDrvName");
     DrvName parsed(name);
     auto attrs = state.buildBindings(2);
-    attrs.alloc(state.s.name).mkString(parsed.name);
-    attrs.alloc("version").mkString(parsed.version);
+    attrs.alloc(state.s.name).mkString(parsed.name, state.mem);
+    attrs.alloc("version").mkString(parsed.version, state.mem);
     v.mkAttrs(attrs);
 }
 
@@ -5048,7 +5050,7 @@ static void prim_splitVersion(EvalState & state, const PosIdx pos, Value ** args
     }
     auto list = state.buildList(components.size());
     for (const auto & [n, component] : enumerate(components))
-        (list[n] = state.allocValue())->mkString(std::move(component));
+        (list[n] = state.allocValue())->mkString(std::move(component), state.mem);
     v.mkList(list);
 }
 
@@ -5192,7 +5194,7 @@ void EvalState::createBaseEnv(const EvalSettings & evalSettings)
         });
 
     if (!settings.pureEval)
-        v.mkString(settings.getCurrentSystem());
+        v.mkString(settings.getCurrentSystem(), mem);
     addConstant(
         "__currentSystem",
         v,
@@ -5224,7 +5226,7 @@ void EvalState::createBaseEnv(const EvalSettings & evalSettings)
             .impureOnly = true,
         });
 
-    v.mkString(nixVersion);
+    v.mkString(nixVersion, mem);
     addConstant(
         "__nixVersion",
         v,
@@ -5249,7 +5251,7 @@ void EvalState::createBaseEnv(const EvalSettings & evalSettings)
         )",
         });
 
-    v.mkString(store->storeDir);
+    v.mkString(store->storeDir, mem);
     addConstant(
         "__storeDir",
         v,
@@ -5314,8 +5316,8 @@ void EvalState::createBaseEnv(const EvalSettings & evalSettings)
     auto list = buildList(lookupPath.elements.size());
     for (const auto & [n, i] : enumerate(lookupPath.elements)) {
         auto attrs = buildBindings(2);
-        attrs.alloc("path").mkString(i.path.s);
-        attrs.alloc("prefix").mkString(i.prefix.s);
+        attrs.alloc("path").mkString(i.path.s, mem);
+        attrs.alloc("prefix").mkString(i.prefix.s, mem);
         (list[n] = allocValue())->mkAttrs(attrs);
     }
     v.mkList(list);
diff --git a/src/libexpr/primops/context.cc b/src/libexpr/primops/context.cc
index 2c5add148..70c13e298 100644
--- a/src/libexpr/primops/context.cc
+++ b/src/libexpr/primops/context.cc
@@ -11,7 +11,7 @@ static void prim_unsafeDiscardStringContext(EvalState & state, const PosIdx pos,
     NixStringContext context;
     auto s = state.coerceToString(
         pos, *args[0], context, "while evaluating the argument passed to builtins.unsafeDiscardStringContext");
-    v.mkString(*s);
+    v.mkString(*s, state.mem);
 }
 
 static RegisterPrimOp primop_unsafeDiscardStringContext({
@@ -218,7 +218,7 @@ static void prim_getContext(EvalState & state, const PosIdx pos, Value ** args,
         if (!info.second.outputs.empty()) {
             auto list = state.buildList(info.second.outputs.size());
             for (const auto & [i, output] : enumerate(info.second.outputs))
-                (list[i] = state.allocValue())->mkString(output);
+                (list[i] = state.allocValue())->mkString(output, state.mem);
             infoAttrs.alloc(state.s.outputs).mkList(list);
         }
         attrs.alloc(state.store->printStorePath(info.first)).mkAttrs(infoAttrs);
diff --git a/src/libexpr/primops/fetchMercurial.cc b/src/libexpr/primops/fetchMercurial.cc
index 2174275ec..cc42931a6 100644
--- a/src/libexpr/primops/fetchMercurial.cc
+++ b/src/libexpr/primops/fetchMercurial.cc
@@ -86,12 +86,12 @@ static void prim_fetchMercurial(EvalState & state, const PosIdx pos, Value ** ar
     auto attrs2 = state.buildBindings(8);
     state.mkStorePathString(storePath, attrs2.alloc(state.s.outPath));
     if (input2.getRef())
-        attrs2.alloc("branch").mkString(*input2.getRef());
+        attrs2.alloc("branch").mkString(*input2.getRef(), state.mem);
     // Backward compatibility: set 'rev' to
     // 0000000000000000000000000000000000000000 for a dirty tree.
     auto rev2 = input2.getRev().value_or(Hash(HashAlgorithm::SHA1));
-    attrs2.alloc("rev").mkString(rev2.gitRev());
-    attrs2.alloc("shortRev").mkString(rev2.gitRev().substr(0, 12));
+    attrs2.alloc("rev").mkString(rev2.gitRev(), state.mem);
+    attrs2.alloc("shortRev").mkString(rev2.gitRev().substr(0, 12), state.mem);
     if (auto revCount = input2.getRevCount())
         attrs2.alloc("revCount").mkInt(*revCount);
     v.mkAttrs(attrs2);
diff --git a/src/libexpr/primops/fetchTree.cc b/src/libexpr/primops/fetchTree.cc
index db976a3e0..1614fcc59 100644
--- a/src/libexpr/primops/fetchTree.cc
+++ b/src/libexpr/primops/fetchTree.cc
@@ -35,7 +35,7 @@ void emitTreeAttrs(
     // FIXME: support arbitrary input attributes.
 
     if (auto narHash = input.getNarHash())
-        attrs.alloc("narHash").mkString(narHash->to_string(HashFormat::SRI, true));
+        attrs.alloc("narHash").mkString(narHash->to_string(HashFormat::SRI, true), state.mem);
 
     if (input.getType() == "git")
         attrs.alloc("submodules").mkBool(fetchers::maybeGetBoolAttr(input.attrs, "submodules").value_or(false));
@@ -43,13 +43,13 @@ void emitTreeAttrs(
     if (!forceDirty) {
 
         if (auto rev = input.getRev()) {
-            attrs.alloc("rev").mkString(rev->gitRev());
-            attrs.alloc("shortRev").mkString(rev->gitShortRev());
+            attrs.alloc("rev").mkString(rev->gitRev(), state.mem);
+            attrs.alloc("shortRev").mkString(rev->gitShortRev(), state.mem);
         } else if (emptyRevFallback) {
             // Backwards compat for `builtins.fetchGit`: dirty repos return an empty sha1 as rev
             auto emptyHash = Hash(HashAlgorithm::SHA1);
-            attrs.alloc("rev").mkString(emptyHash.gitRev());
-            attrs.alloc("shortRev").mkString(emptyHash.gitShortRev());
+            attrs.alloc("rev").mkString(emptyHash.gitRev(), state.mem);
+            attrs.alloc("shortRev").mkString(emptyHash.gitShortRev(), state.mem);
         }
 
         if (auto revCount = input.getRevCount())
@@ -59,13 +59,14 @@ void emitTreeAttrs(
     }
 
     if (auto dirtyRev = fetchers::maybeGetStrAttr(input.attrs, "dirtyRev")) {
-        attrs.alloc("dirtyRev").mkString(*dirtyRev);
-        attrs.alloc("dirtyShortRev").mkString(*fetchers::maybeGetStrAttr(input.attrs, "dirtyShortRev"));
+        attrs.alloc("dirtyRev").mkString(*dirtyRev, state.mem);
+        attrs.alloc("dirtyShortRev").mkString(*fetchers::maybeGetStrAttr(input.attrs, "dirtyShortRev"), state.mem);
     }
 
     if (auto lastModified = input.getLastModified()) {
         attrs.alloc("lastModified").mkInt(*lastModified);
-        attrs.alloc("lastModifiedDate").mkString(fmt("%s", std::put_time(std::gmtime(&*lastModified), "%Y%m%d%H%M%S")));
+        attrs.alloc("lastModifiedDate")
+            .mkString(fmt("%s", std::put_time(std::gmtime(&*lastModified), "%Y%m%d%H%M%S")), state.mem);
     }
 
     v.mkAttrs(attrs);
diff --git a/src/libexpr/primops/fromTOML.cc b/src/libexpr/primops/fromTOML.cc
index a06224fee..562ff3d14 100644
--- a/src/libexpr/primops/fromTOML.cc
+++ b/src/libexpr/primops/fromTOML.cc
@@ -126,7 +126,7 @@ static void prim_fromTOML(EvalState & state, const PosIdx pos, Value ** args, Va
         case toml::value_t::string: {
             auto s = toml::get<std::string_view>(t);
             forceNoNullByte(s);
-            v.mkString(s);
+            v.mkString(s, state.mem);
         } break;
         case toml::value_t::local_datetime:
         case toml::value_t::offset_datetime:
@@ -142,7 +142,7 @@ static void prim_fromTOML(EvalState & state, const PosIdx pos, Value ** args, Va
                 s << t;
                 auto str = s.view();
                 forceNoNullByte(str);
-                attrs.alloc("value").mkString(str);
+                attrs.alloc("value").mkString(str, state.mem);
                 v.mkAttrs(attrs);
             } else {
                 throw std::runtime_error("Dates and times are not supported");
diff --git a/src/libflake-c/nix_api_flake.cc b/src/libflake-c/nix_api_flake.cc
index 2de0e667e..32329585a 100644
--- a/src/libflake-c/nix_api_flake.cc
+++ b/src/libflake-c/nix_api_flake.cc
@@ -200,7 +200,7 @@ nix_value * nix_locked_flake_get_output_attrs(
     nix_clear_err(context);
     try {
         auto v = nix_alloc_value(context, evalState);
-        nix::flake::callFlake(evalState->state, *lockedFlake->lockedFlake, v->value);
+        nix::flake::callFlake(evalState->state, *lockedFlake->lockedFlake, *v->value);
         return v;
     }
     NIXC_CATCH_ERRS_NULL
diff --git a/src/libflake/flake-primops.cc b/src/libflake/flake-primops.cc
index 3f65dc47a..962edbb3d 100644
--- a/src/libflake/flake-primops.cc
+++ b/src/libflake/flake-primops.cc
@@ -93,7 +93,7 @@ static void prim_parseFlakeRef(EvalState & state, const PosIdx pos, Value ** arg
         auto & vv = binds.alloc(s);
         std::visit(
             overloaded{
-                [&vv](const std::string & value) { vv.mkString(value); },
+                [&vv, &state](const std::string & value) { vv.mkString(value, state.mem); },
                 [&vv](const uint64_t & value) { vv.mkInt(value); },
                 [&vv](const Explicit<bool> & value) { vv.mkBool(value.t); }},
             value);
@@ -156,7 +156,7 @@ static void prim_flakeRefToString(EvalState & state, const PosIdx pos, Value **
         }
     }
     auto flakeRef = FlakeRef::fromAttrs(state.fetchSettings, attrs);
-    v.mkString(flakeRef.to_string());
+    v.mkString(flakeRef.to_string(), state.mem);
 }
 
 nix::PrimOp flakeRefToString({
diff --git a/src/libflake/flake.cc b/src/libflake/flake.cc
index 6e5fa6ca1..9f7476bd0 100644
--- a/src/libflake/flake.cc
+++ b/src/libflake/flake.cc
@@ -956,7 +956,7 @@ void callFlake(EvalState & state, const LockedFlake & lockedFlake, Value & vRes)
         auto key = keyMap.find(node);
         assert(key != keyMap.end());
 
-        override.alloc(state.symbols.create("dir")).mkString(CanonPath(subdir).rel());
+        override.alloc(state.symbols.create("dir")).mkString(CanonPath(subdir).rel(), state.mem);
 
         overrides.alloc(state.symbols.create(key->second)).mkAttrs(override);
     }
@@ -966,7 +966,7 @@ void callFlake(EvalState & state, const LockedFlake & lockedFlake, Value & vRes)
     Value * vCallFlake = requireInternalFile(state, CanonPath("call-flake.nix"));
 
     auto vLocks = state.allocValue();
-    vLocks->mkString(lockFileStr);
+    vLocks->mkString(lockFileStr, state.mem);
 
     auto vFetchFinalTree = get(state.internalPrimOps, "fetchFinalTree");
     assert(vFetchFinalTree);
diff --git a/src/nix/main.cc b/src/nix/main.cc
index 945cce9ac..1d7066449 100644
--- a/src/nix/main.cc
+++ b/src/nix/main.cc
@@ -271,7 +271,7 @@ static void showHelp(std::vector<std::string> subcommand, NixArgs & toplevel)
     );
 
     auto vDump = state.allocValue();
-    vDump->mkString(toplevel.dumpCli());
+    vDump->mkString(toplevel.dumpCli(), state.mem);
 
     auto vRes = state.allocValue();
     Value * args[]{&state.getBuiltin("false"), vDump};
diff --git a/src/nix/nix-env/nix-env.cc b/src/nix/nix-env/nix-env.cc
index 2a0984d18..54443a22c 100644
--- a/src/nix/nix-env/nix-env.cc
+++ b/src/nix/nix-env/nix-env.cc
@@ -132,7 +132,7 @@ static void getAllExprs(EvalState & state, const SourcePath & path, StringSet &
             }
             /* Load the expression on demand. */
             auto vArg = state.allocValue();
-            vArg->mkPath(path2);
+            vArg->mkPath(path2, state.mem);
             if (seen.size() == maxAttrs)
                 throw Error("too many Nix expressions in directory '%1%'", path);
             attrs.alloc(attrName).mkApp(&state.getBuiltin("import"), vArg);
@@ -483,7 +483,7 @@ static bool keep(PackageInfo & drv)
 static void setMetaFlag(EvalState & state, PackageInfo & drv, const std::string & name, const std::string & value)
 {
     auto v = state.allocValue();
-    v->mkString(value);
+    v->mkString(value, state.mem);
     drv.setMeta(name, v);
 }
 
diff --git a/src/nix/nix-env/user-env.cc b/src/nix/nix-env/user-env.cc
index 21fdf25bc..d09365073 100644
--- a/src/nix/nix-env/user-env.cc
+++ b/src/nix/nix-env/user-env.cc
@@ -58,20 +58,20 @@ bool createUserEnv(
         auto attrs = state.buildBindings(7 + outputs.size());
 
         attrs.alloc(state.s.type).mkStringNoCopy("derivation"_sds);
-        attrs.alloc(state.s.name).mkString(i.queryName());
+        attrs.alloc(state.s.name).mkString(i.queryName(), state.mem);
         auto system = i.querySystem();
         if (!system.empty())
-            attrs.alloc(state.s.system).mkString(system);
-        attrs.alloc(state.s.outPath).mkString(state.store->printStorePath(i.queryOutPath()));
+            attrs.alloc(state.s.system).mkString(system, state.mem);
+        attrs.alloc(state.s.outPath).mkString(state.store->printStorePath(i.queryOutPath()), state.mem);
         if (drvPath)
-            attrs.alloc(state.s.drvPath).mkString(state.store->printStorePath(*drvPath));
+            attrs.alloc(state.s.drvPath).mkString(state.store->printStorePath(*drvPath), state.mem);
 
         // Copy each output meant for installation.
         auto outputsList = state.buildList(outputs.size());
         for (const auto & [m, j] : enumerate(outputs)) {
-            (outputsList[m] = state.allocValue())->mkString(j.first);
+            (outputsList[m] = state.allocValue())->mkString(j.first, state.mem);
             auto outputAttrs = state.buildBindings(2);
-            outputAttrs.alloc(state.s.outPath).mkString(state.store->printStorePath(*j.second));
+            outputAttrs.alloc(state.s.outPath).mkString(state.store->printStorePath(*j.second), state.mem);
             attrs.alloc(j.first).mkAttrs(outputAttrs);
 
             /* This is only necessary when installing store paths, e.g.,