diff --git a/prometeu-compiler/frontends/prometeu-frontend-pbs/src/main/java/p/studio/compiler/pbs/PbsFrontendCompiler.java b/prometeu-compiler/frontends/prometeu-frontend-pbs/src/main/java/p/studio/compiler/pbs/PbsFrontendCompiler.java
index 78687576..2a190660 100644
--- a/prometeu-compiler/frontends/prometeu-frontend-pbs/src/main/java/p/studio/compiler/pbs/PbsFrontendCompiler.java
+++ b/prometeu-compiler/frontends/prometeu-frontend-pbs/src/main/java/p/studio/compiler/pbs/PbsFrontendCompiler.java
@@ -3,6 +3,7 @@ package p.studio.compiler.pbs;
 import p.studio.compiler.models.IRFunction;
 import p.studio.compiler.models.SourceKind;
 import p.studio.compiler.models.IRBackendFile;
+import p.studio.compiler.models.IRBackendExecutableFunction;
 import p.studio.compiler.messages.HostAdmissionContext;
 import p.studio.compiler.models.IRReservedMetadata;
 import p.studio.compiler.pbs.ast.PbsAst;
@@ -16,6 +17,9 @@ import p.studio.compiler.source.identifiers.FileId;
 import p.studio.utilities.structures.ReadOnlyList;
 
 import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
 
 public final class PbsFrontendCompiler {
     private final PbsDeclarationSemanticsValidator declarationSemanticsValidator = new PbsDeclarationSemanticsValidator();
@@ -61,7 +65,7 @@ public final class PbsFrontendCompiler {
             final FileId fileId,
             final PbsAst.File ast,
             final DiagnosticSink diagnostics) {
-        return compileParsedFile(fileId, ast, diagnostics, SourceKind.PROJECT);
+        return compileParsedFile(fileId, ast, diagnostics, SourceKind.PROJECT, "", HostAdmissionContext.permissiveDefault());
     }
 
     public IRBackendFile compileParsedFile(
@@ -69,7 +73,7 @@ public final class PbsFrontendCompiler {
             final PbsAst.File ast,
             final DiagnosticSink diagnostics,
             final SourceKind sourceKind) {
-        return compileParsedFile(fileId, ast, diagnostics, sourceKind, HostAdmissionContext.permissiveDefault());
+        return compileParsedFile(fileId, ast, diagnostics, sourceKind, "", HostAdmissionContext.permissiveDefault());
     }
 
     public IRBackendFile compileParsedFile(
@@ -78,6 +82,16 @@ public final class PbsFrontendCompiler {
             final DiagnosticSink diagnostics,
             final SourceKind sourceKind,
             final HostAdmissionContext hostAdmissionContext) {
+        return compileParsedFile(fileId, ast, diagnostics, sourceKind, "", hostAdmissionContext);
+    }
+
+    public IRBackendFile compileParsedFile(
+            final FileId fileId,
+            final PbsAst.File ast,
+            final DiagnosticSink diagnostics,
+            final SourceKind sourceKind,
+            final String moduleKey,
+            final HostAdmissionContext hostAdmissionContext) {
         final var semanticsErrorBaseline = diagnostics.errorCount();
         declarationSemanticsValidator.validate(ast, sourceKind, diagnostics);
         flowSemanticsValidator.validate(ast, diagnostics);
@@ -103,7 +117,10 @@ public final class PbsFrontendCompiler {
         final ReadOnlyList<IRFunction> functions = sourceKind == SourceKind.SDK_INTERFACE
                 ? ReadOnlyList.empty()
                 : lowerFunctions(fileId, ast);
-        return new IRBackendFile(fileId, functions, reservedMetadata);
+        final ReadOnlyList<IRBackendExecutableFunction> executableFunctions = sourceKind == SourceKind.SDK_INTERFACE
+                ? ReadOnlyList.empty()
+                : lowerExecutableFunctions(fileId, ast, moduleKey, reservedMetadata);
+        return new IRBackendFile(fileId, functions, executableFunctions, reservedMetadata);
     }
 
     private ReadOnlyList<IRFunction> lowerFunctions(final FileId fileId, final PbsAst.File ast) {
@@ -118,4 +135,258 @@ public final class PbsFrontendCompiler {
         }
         return ReadOnlyList.wrap(functions);
     }
+
+    private ReadOnlyList<IRBackendExecutableFunction> lowerExecutableFunctions(
+            final FileId fileId,
+            final PbsAst.File ast,
+            final String moduleKey,
+            final IRReservedMetadata reservedMetadata) {
+        final var hostByMethodName = new HashMap<String, IRReservedMetadata.HostMethodBinding>();
+        for (final var hostBinding : reservedMetadata.hostMethodBindings()) {
+            hostByMethodName.put(hostBinding.sourceMethodName(), hostBinding);
+        }
+        final var intrinsicByMethodName = new HashMap<String, IRReservedMetadata.IntrinsicSurface>();
+        for (final var builtinType : reservedMetadata.builtinTypeSurfaces()) {
+            for (final var intrinsicSurface : builtinType.intrinsics()) {
+                intrinsicByMethodName.put(intrinsicSurface.sourceMethodName(), intrinsicSurface);
+            }
+        }
+
+        final var executableFunctions = new ArrayList<IRBackendExecutableFunction>(ast.functions().size());
+        for (final var fn : ast.functions()) {
+            final var instructions = new ArrayList<IRBackendExecutableFunction.Instruction>();
+            final var callsites = new ArrayList<PbsAst.CallExpr>();
+            collectCallsFromBlock(fn.body(), callsites);
+            for (final var callExpr : callsites) {
+                final var calleeName = extractSimpleCalleeName(callExpr.callee());
+                final var host = hostByMethodName.get(calleeName);
+                if (host != null) {
+                    instructions.add(new IRBackendExecutableFunction.Instruction(
+                            IRBackendExecutableFunction.InstructionKind.CALL_HOST,
+                            "",
+                            "",
+                            new IRBackendExecutableFunction.HostCallMetadata(
+                                    host.abiModule(),
+                                    host.abiMethod(),
+                                    host.abiVersion(),
+                                    callExpr.arguments().size(),
+                                    0),
+                            null,
+                            callExpr.span()));
+                    continue;
+                }
+
+                final var intrinsic = intrinsicByMethodName.get(calleeName);
+                if (intrinsic != null) {
+                    instructions.add(new IRBackendExecutableFunction.Instruction(
+                            IRBackendExecutableFunction.InstructionKind.CALL_INTRINSIC,
+                            "",
+                            "",
+                            null,
+                            new IRBackendExecutableFunction.IntrinsicCallMetadata(
+                                    intrinsic.canonicalName(),
+                                    intrinsic.canonicalVersion(),
+                                    intrinsicIdFor(intrinsic.canonicalName(), intrinsic.canonicalVersion())),
+                            callExpr.span()));
+                    continue;
+                }
+
+                instructions.add(new IRBackendExecutableFunction.Instruction(
+                        IRBackendExecutableFunction.InstructionKind.CALL_FUNC,
+                        moduleKey == null ? "" : moduleKey,
+                        calleeName,
+                        null,
+                        null,
+                        callExpr.span()));
+            }
+            instructions.add(new IRBackendExecutableFunction.Instruction(
+                    IRBackendExecutableFunction.InstructionKind.RET,
+                    "",
+                    "",
+                    null,
+                    null,
+                    fn.span()));
+
+            final var returnSlots = switch (fn.returnKind()) {
+                case INFERRED_UNIT, EXPLICIT_UNIT -> 0;
+                case PLAIN, RESULT -> 1;
+            };
+            final var start = safeToInt(fn.span().getStart());
+            final var end = safeToInt(fn.span().getEnd());
+            executableFunctions.add(new IRBackendExecutableFunction(
+                    fileId,
+                    moduleKey == null ? "" : moduleKey,
+                    fn.name(),
+                    start,
+                    end,
+                    fn.parameters().size(),
+                    0,
+                    returnSlots,
+                    Math.max(4, fn.parameters().size() + 2),
+                    ReadOnlyList.wrap(instructions),
+                    fn.span()));
+        }
+        return ReadOnlyList.wrap(executableFunctions);
+    }
+
+    private int intrinsicIdFor(
+            final String canonicalName,
+            final long canonicalVersion) {
+        return (canonicalName + "#" + canonicalVersion).hashCode();
+    }
+
+    private int safeToInt(final long value) {
+        if (value > Integer.MAX_VALUE) {
+            return Integer.MAX_VALUE;
+        }
+        if (value < Integer.MIN_VALUE) {
+            return Integer.MIN_VALUE;
+        }
+        return (int) value;
+    }
+
+    private void collectCallsFromBlock(
+            final PbsAst.Block block,
+            final List<PbsAst.CallExpr> output) {
+        for (final var statement : block.statements()) {
+            collectCallsFromStatement(statement, output);
+        }
+        if (block.tailExpression() != null) {
+            collectCallsFromExpression(block.tailExpression(), output);
+        }
+    }
+
+    private void collectCallsFromStatement(
+            final PbsAst.Statement statement,
+            final List<PbsAst.CallExpr> output) {
+        switch (statement) {
+            case PbsAst.LetStatement letStatement -> collectCallsFromExpression(letStatement.initializer(), output);
+            case PbsAst.AssignStatement assignStatement -> collectCallsFromExpression(assignStatement.value(), output);
+            case PbsAst.ReturnStatement returnStatement -> {
+                if (returnStatement.value() != null) {
+                    collectCallsFromExpression(returnStatement.value(), output);
+                }
+            }
+            case PbsAst.IfStatement ifStatement -> {
+                collectCallsFromExpression(ifStatement.condition(), output);
+                collectCallsFromBlock(ifStatement.thenBlock(), output);
+                if (ifStatement.elseIf() != null) {
+                    collectCallsFromStatement(ifStatement.elseIf(), output);
+                }
+                if (ifStatement.elseBlock() != null) {
+                    collectCallsFromBlock(ifStatement.elseBlock(), output);
+                }
+            }
+            case PbsAst.ForStatement forStatement -> {
+                collectCallsFromExpression(forStatement.fromExpression(), output);
+                collectCallsFromExpression(forStatement.untilExpression(), output);
+                if (forStatement.stepExpression() != null) {
+                    collectCallsFromExpression(forStatement.stepExpression(), output);
+                }
+                collectCallsFromBlock(forStatement.body(), output);
+            }
+            case PbsAst.WhileStatement whileStatement -> {
+                collectCallsFromExpression(whileStatement.condition(), output);
+                collectCallsFromBlock(whileStatement.body(), output);
+            }
+            case PbsAst.ExpressionStatement expressionStatement ->
+                    collectCallsFromExpression(expressionStatement.expression(), output);
+            case PbsAst.BreakStatement ignored -> {
+            }
+            case PbsAst.ContinueStatement ignored -> {
+            }
+        }
+    }
+
+    private void collectCallsFromExpression(
+            final PbsAst.Expression expression,
+            final List<PbsAst.CallExpr> output) {
+        switch (expression) {
+            case PbsAst.CallExpr callExpr -> {
+                output.add(callExpr);
+                collectCallsFromExpression(callExpr.callee(), output);
+                for (final var arg : callExpr.arguments()) {
+                    collectCallsFromExpression(arg, output);
+                }
+            }
+            case PbsAst.ApplyExpr applyExpr -> {
+                collectCallsFromExpression(applyExpr.callee(), output);
+                collectCallsFromExpression(applyExpr.argument(), output);
+            }
+            case PbsAst.BinaryExpr binaryExpr -> {
+                collectCallsFromExpression(binaryExpr.left(), output);
+                collectCallsFromExpression(binaryExpr.right(), output);
+            }
+            case PbsAst.UnaryExpr unaryExpr -> collectCallsFromExpression(unaryExpr.expression(), output);
+            case PbsAst.ElseExpr elseExpr -> {
+                collectCallsFromExpression(elseExpr.optionalExpression(), output);
+                collectCallsFromExpression(elseExpr.fallbackExpression(), output);
+            }
+            case PbsAst.IfExpr ifExpr -> {
+                collectCallsFromExpression(ifExpr.condition(), output);
+                collectCallsFromBlock(ifExpr.thenBlock(), output);
+                collectCallsFromExpression(ifExpr.elseExpression(), output);
+            }
+            case PbsAst.SwitchExpr switchExpr -> {
+                collectCallsFromExpression(switchExpr.selector(), output);
+                for (final var arm : switchExpr.arms()) {
+                    collectCallsFromBlock(arm.block(), output);
+                }
+            }
+            case PbsAst.HandleExpr handleExpr -> {
+                collectCallsFromExpression(handleExpr.value(), output);
+                for (final var arm : handleExpr.arms()) {
+                    collectCallsFromBlock(arm.block(), output);
+                }
+            }
+            case PbsAst.AsExpr asExpr -> collectCallsFromExpression(asExpr.expression(), output);
+            case PbsAst.MemberExpr memberExpr -> collectCallsFromExpression(memberExpr.receiver(), output);
+            case PbsAst.PropagateExpr propagateExpr -> collectCallsFromExpression(propagateExpr.expression(), output);
+            case PbsAst.GroupExpr groupExpr -> collectCallsFromExpression(groupExpr.expression(), output);
+            case PbsAst.NewExpr newExpr -> {
+                for (final var arg : newExpr.arguments()) {
+                    collectCallsFromExpression(arg, output);
+                }
+            }
+            case PbsAst.BindExpr bindExpr -> collectCallsFromExpression(bindExpr.contextExpression(), output);
+            case PbsAst.SomeExpr someExpr -> collectCallsFromExpression(someExpr.value(), output);
+            case PbsAst.OkExpr okExpr -> collectCallsFromExpression(okExpr.value(), output);
+            case PbsAst.TupleExpr tupleExpr -> {
+                for (final var item : tupleExpr.items()) {
+                    collectCallsFromExpression(item.expression(), output);
+                }
+            }
+            case PbsAst.BlockExpr blockExpr -> collectCallsFromBlock(blockExpr.block(), output);
+            case PbsAst.IdentifierExpr ignored -> {
+            }
+            case PbsAst.IntLiteralExpr ignored -> {
+            }
+            case PbsAst.FloatLiteralExpr ignored -> {
+            }
+            case PbsAst.BoundedLiteralExpr ignored -> {
+            }
+            case PbsAst.StringLiteralExpr ignored -> {
+            }
+            case PbsAst.BoolLiteralExpr ignored -> {
+            }
+            case PbsAst.ThisExpr ignored -> {
+            }
+            case PbsAst.NoneExpr ignored -> {
+            }
+            case PbsAst.ErrExpr ignored -> {
+            }
+            case PbsAst.UnitExpr ignored -> {
+            }
+        }
+    }
+
+    private String extractSimpleCalleeName(final PbsAst.Expression callee) {
+        return switch (callee) {
+            case PbsAst.IdentifierExpr identifierExpr -> identifierExpr.name();
+            case PbsAst.MemberExpr memberExpr -> memberExpr.memberName();
+            case PbsAst.BindExpr bindExpr -> bindExpr.functionName();
+            case PbsAst.GroupExpr groupExpr -> extractSimpleCalleeName(groupExpr.expression());
+            default -> "<unknown>";
+        };
+    }
 }
diff --git a/prometeu-compiler/frontends/prometeu-frontend-pbs/src/main/java/p/studio/compiler/services/PBSFrontendPhaseService.java b/prometeu-compiler/frontends/prometeu-frontend-pbs/src/main/java/p/studio/compiler/services/PBSFrontendPhaseService.java
index ccda745e..c0aee957 100644
--- a/prometeu-compiler/frontends/prometeu-frontend-pbs/src/main/java/p/studio/compiler/services/PBSFrontendPhaseService.java
+++ b/prometeu-compiler/frontends/prometeu-frontend-pbs/src/main/java/p/studio/compiler/services/PBSFrontendPhaseService.java
@@ -148,6 +148,7 @@ public class PBSFrontendPhaseService implements FrontendPhaseService {
                     parsedSource.ast(),
                     diagnostics,
                     parsedSource.sourceKind(),
+                    parsedSource.moduleKey(),
                     ctx.hostAdmissionContext());
             if (diagnostics.errorCount() > compileErrorBaseline) {
                 failedModuleKeys.add(parsedSource.moduleKey());
diff --git a/prometeu-compiler/frontends/prometeu-frontend-pbs/src/test/java/p/studio/compiler/pbs/PbsFrontendCompilerTest.java b/prometeu-compiler/frontends/prometeu-frontend-pbs/src/test/java/p/studio/compiler/pbs/PbsFrontendCompilerTest.java
index f30a4a6c..60fc11c4 100644
--- a/prometeu-compiler/frontends/prometeu-frontend-pbs/src/test/java/p/studio/compiler/pbs/PbsFrontendCompilerTest.java
+++ b/prometeu-compiler/frontends/prometeu-frontend-pbs/src/test/java/p/studio/compiler/pbs/PbsFrontendCompilerTest.java
@@ -72,6 +72,32 @@ class PbsFrontendCompilerTest {
         assertEquals(2, fileBackend.functions().size());
     }
 
+    @Test
+    void shouldLowerExecutableFunctionsWithCallsiteCategories() {
+        final var source = """
+                fn b(x: int) -> int {
+                  return x;
+                }
+
+                fn a() -> int {
+                  return b(1);
+                }
+                """;
+
+        final var diagnostics = DiagnosticSink.empty();
+        final var compiler = new PbsFrontendCompiler();
+        final var fileBackend = compiler.compileFile(new FileId(42), source, diagnostics);
+
+        assertTrue(diagnostics.isEmpty(), "Valid program should not report diagnostics");
+        assertEquals(2, fileBackend.executableFunctions().size());
+        final var executableA = fileBackend.executableFunctions().stream()
+                .filter(fn -> fn.callableName().equals("a"))
+                .findFirst()
+                .orElseThrow();
+        assertTrue(executableA.instructions().stream().anyMatch(i ->
+                i.kind() == p.studio.compiler.models.IRBackendExecutableFunction.InstructionKind.CALL_FUNC));
+    }
+
     @Test
     void shouldNotLowerWhenSyntaxErrorsExist() {
         final var source = """