diff --git a/package-lock.json b/package-lock.json
index fa21b1399..c1aea339e 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -9160,6 +9160,7 @@
         "@typeberry/database": "*",
         "@typeberry/executor": "*",
         "@typeberry/hash": "*",
+        "@typeberry/jam-host-calls": "*",
         "@typeberry/logger": "*",
         "@typeberry/numbers": "*",
         "@typeberry/state": "*",
diff --git a/packages/jam/block/work-item-segment.ts b/packages/jam/block/work-item-segment.ts
index e804dd591..319ed1437 100644
--- a/packages/jam/block/work-item-segment.ts
+++ b/packages/jam/block/work-item-segment.ts
@@ -2,17 +2,35 @@ import type { Bytes } from "@typeberry/bytes";
 import { tryAsU16, type U16 } from "@typeberry/numbers";
 import { asOpaqueType, type Opaque } from "@typeberry/utils";
 
-/** `W_E`: The basic size of erasure-coded pieces in octets. See equation H.6. */
+/**
+ * `W_E`: The basic size of erasure-coded pieces in octets. See equation H.6.
+ * https://graypaper.fluffylabs.dev/#/ab2cdbd/449600449700?v=0.7.2
+ */
 export const W_E = 684;
 
-/** `W_S`: The size of an exported segment in erasure-coded pieces in octets. */
-export const W_S = 6;
+/**
+ * `W_P`: The size of an exported segment in erasure-coded pieces in octets.
+ * https://graypaper.fluffylabs.dev/#/ab2cdbd/44b10044b200?v=0.7.2
+ */
+export const W_P = 6;
 
-/** `W_M`: The maximum number of entries in a work-package manifest. */
-export const MAX_NUMBER_OF_SEGMENTS = 2048; // 2**11
+/**
+ * `W_M`: The maximum number of imports in a work-package manifest.
+ * https://graypaper.fluffylabs.dev/#/ab2cdbd/44ad0044ae00?v=0.7.2
+ */
+export const MAX_NUMBER_OF_IMPORTS_WP = 3072;
 
-/** `W_E * W_S`: Exported segment size in bytes. */
-export const SEGMENT_BYTES = W_E * W_S;
+/**
+ * `W_X`: The maximum number of exports in a work-package manifest.
+ * https://graypaper.fluffylabs.dev/#/ab2cdbd/44be0044bf00?v=0.7.2
+ */
+export const MAX_NUMBER_OF_EXPORTS_WP = 3072;
+
+/**
+ * `W_G = W_E * W_P`: Exported segment size in bytes.
+ * https://graypaper.fluffylabs.dev/#/ab2cdbd/449a00449b00?v=0.7.2
+ */
+export const SEGMENT_BYTES = W_E * W_P;
 export type SEGMENT_BYTES = typeof SEGMENT_BYTES;
 
 /** Exported segment data. */
diff --git a/packages/jam/block/work-item.ts b/packages/jam/block/work-item.ts
index 80a542f1b..5908671c6 100644
--- a/packages/jam/block/work-item.ts
+++ b/packages/jam/block/work-item.ts
@@ -7,7 +7,7 @@ import { type Opaque, WithDebug } from "@typeberry/utils";
 import { codecKnownSizeArray } from "./codec-utils.js";
 import type { ServiceGas, ServiceId } from "./common.js";
 import type { CodeHash } from "./hash.js";
-import { MAX_NUMBER_OF_SEGMENTS, type SegmentIndex } from "./work-item-segment.js";
+import { MAX_NUMBER_OF_IMPORTS_WP, type SegmentIndex } from "./work-item-segment.js";
 
 type WorkItemExtrinsicHash = Opaque<OpaqueHash, "ExtrinsicHash">;
 
@@ -126,13 +126,17 @@ export class WorkItem extends WithDebug {
     codeHash: codec.bytes(HASH_SIZE).asOpaque<CodeHash>(),
     refineGasLimit: codec.u64.asOpaque<ServiceGas>(),
     accumulateGasLimit: codec.u64.asOpaque<ServiceGas>(),
+    // TODO: [MaSo] It should be validated to not exceed W_X
+    // https://graypaper.fluffylabs.dev/#/ab2cdbd/1a0b011a1c01?v=0.7.2
     exportCount: codec.u16,
     payload: codec.blob,
     importSegments: codecKnownSizeArray(ImportSpec.Codec, {
       minLength: 0,
-      maxLength: MAX_NUMBER_OF_SEGMENTS,
-      typicalLength: MAX_NUMBER_OF_SEGMENTS,
+      maxLength: MAX_NUMBER_OF_IMPORTS_WP,
+      typicalLength: MAX_NUMBER_OF_IMPORTS_WP,
     }),
+    // TODO: [MaSo] It should be validated to not exceed T = 128
+    // https://graypaper.fluffylabs.dev/#/ab2cdbd/1a0b011a1c01?v=0.7.2
     extrinsic: codec.sequenceVarLen(WorkItemExtrinsicSpec.Codec),
   });
 
@@ -175,7 +179,7 @@ export class WorkItem extends WithDebug {
     /** `a`: accumulate execution gas limit */
     public readonly accumulateGasLimit: ServiceGas,
     /** `i`: sequence of imported data segments, which identify a prior exported segment. */
-    public readonly importSegments: KnownSizeArray<ImportSpec, `Less than ${typeof MAX_NUMBER_OF_SEGMENTS}`>,
+    public readonly importSegments: KnownSizeArray<ImportSpec, `Less than ${typeof MAX_NUMBER_OF_IMPORTS_WP}`>,
     /** `x`: sequence of blob hashes and lengths to be introduced in this block */
     public readonly extrinsic: WorkItemExtrinsicSpec[],
     /** `e`: number of data segments exported by this work item. */
diff --git a/packages/jam/in-core/externalities/refine.test.ts b/packages/jam/in-core/externalities/refine.test.ts
index ec11deea8..cb30bbad5 100644
--- a/packages/jam/in-core/externalities/refine.test.ts
+++ b/packages/jam/in-core/externalities/refine.test.ts
@@ -1,14 +1,34 @@
 import assert from "node:assert";
 import { describe, it } from "node:test";
-import { type PreimageHash, type ServiceId, tryAsServiceGas, tryAsServiceId, tryAsTimeSlot } from "@typeberry/block";
+import {
+  MAX_NUMBER_OF_EXPORTS_WP,
+  type PreimageHash,
+  SEGMENT_BYTES,
+  type Segment,
+  type ServiceId,
+  tryAsServiceGas,
+  tryAsServiceId,
+  tryAsTimeSlot,
+} from "@typeberry/block";
 import { Bytes, BytesBlob } from "@typeberry/bytes";
 import { HashDictionary } from "@typeberry/collections";
 import { tinyChainSpec } from "@typeberry/config";
 import { HASH_SIZE } from "@typeberry/hash";
+import { SegmentExportError } from "@typeberry/jam-host-calls";
 import { tryAsU32, tryAsU64 } from "@typeberry/numbers";
 import { InMemoryService, InMemoryState, PreimageItem, ServiceAccountInfo, type State } from "@typeberry/state";
 import { RefineExternalitiesImpl, type RefineExternalitiesParams } from "./refine.js";
 
+function createSegment(byte = 0xab): Segment {
+  return Bytes.fill(SEGMENT_BYTES, byte);
+}
+
+function createSmallSegment(bytes: number[]): Segment {
+  const data = new Uint8Array(SEGMENT_BYTES);
+  data.set(bytes);
+  return Bytes.fromBlob(data, SEGMENT_BYTES);
+}
+
 /**
  * Create a mock State that has specified services with preimages.
  */
@@ -60,6 +80,7 @@ function createExt(overrides: Partial<RefineExternalitiesParams> = {}) {
   return RefineExternalitiesImpl.create({
     currentServiceId: tryAsServiceId(42),
     lookupState: overrides.lookupState ?? defaultState,
+    exportOffset: overrides.exportOffset ?? 0,
     ...overrides,
   });
 }
@@ -123,4 +144,72 @@ describe("RefineExternalitiesImpl", () => {
       assert.strictEqual(r2?.raw[0], 0x02);
     });
   });
+
+  describe("exportSegment", () => {
+    it("should export a segment and return its index", () => {
+      const ext = createExt();
+      const segment = createSegment(0x01);
+      const result = ext.exportSegment(segment);
+
+      assert.strictEqual(result.isOk, true);
+      assert.strictEqual(result.ok, 0); // first export at offset 0
+      assert.strictEqual(ext.getExportedSegments().length, 1);
+    });
+
+    it("should return sequential indices for multiple exports", () => {
+      const ext = createExt();
+
+      const r1 = ext.exportSegment(createSegment(0x01));
+      const r2 = ext.exportSegment(createSegment(0x02));
+      const r3 = ext.exportSegment(createSegment(0x03));
+
+      assert.strictEqual(r1.isOk, true);
+      assert.strictEqual(r1.ok, 0);
+      assert.strictEqual(r2.isOk, true);
+      assert.strictEqual(r2.ok, 1);
+      assert.strictEqual(r3.isOk, true);
+      assert.strictEqual(r3.ok, 2);
+      assert.strictEqual(ext.getExportedSegments().length, 3);
+    });
+
+    it("should apply exportOffset to segment indices", () => {
+      const ext = createExt({ exportOffset: 100 });
+      const result = ext.exportSegment(createSegment());
+
+      assert.strictEqual(result.isOk, true);
+      assert.strictEqual(result.ok, 100);
+    });
+
+    it("should return SegmentExportError when MAX_NUMBER_OF_EXPORTS_WP exceeded", () => {
+      const ext = createExt({ exportOffset: MAX_NUMBER_OF_EXPORTS_WP });
+      const result = ext.exportSegment(createSegment());
+
+      assert.strictEqual(result.isError, true);
+      assert.strictEqual(result.error, SegmentExportError);
+    });
+
+    it("should return SegmentExportError at exactly MAX_NUMBER_OF_EXPORTS_WP - 1 + 1", () => {
+      const ext = createExt({ exportOffset: MAX_NUMBER_OF_EXPORTS_WP - 1 });
+
+      // This one should succeed (index = MAX_NUMBER_OF_EXPORTS_WP - 1)
+      const r1 = ext.exportSegment(createSegment(0x01));
+      assert.strictEqual(r1.isOk, true);
+      assert.strictEqual(r1.ok, MAX_NUMBER_OF_EXPORTS_WP - 1);
+
+      // This one should fail
+      const r2 = ext.exportSegment(createSegment(0x02));
+      assert.strictEqual(r2.isError, true);
+      assert.strictEqual(r2.error, SegmentExportError);
+    });
+
+    it("should store exact segment data", () => {
+      const ext = createExt();
+      const segment = createSmallSegment([1, 2, 3, 4, 5]);
+      ext.exportSegment(segment);
+
+      const exported = ext.getExportedSegments();
+      assert.strictEqual(exported.length, 1);
+      assert.deepStrictEqual(exported[0].raw.subarray(0, 5), new Uint8Array([1, 2, 3, 4, 5]));
+    });
+  });
 });
diff --git a/packages/jam/in-core/externalities/refine.ts b/packages/jam/in-core/externalities/refine.ts
index 452aca46c..d202373fe 100644
--- a/packages/jam/in-core/externalities/refine.ts
+++ b/packages/jam/in-core/externalities/refine.ts
@@ -1,24 +1,30 @@
-import type { Segment, SegmentIndex, ServiceId } from "@typeberry/block";
+import {
+  MAX_NUMBER_OF_EXPORTS_WP,
+  type Segment,
+  type SegmentIndex,
+  type ServiceId,
+  tryAsSegmentIndex,
+} from "@typeberry/block";
 import type { BytesBlob } from "@typeberry/bytes";
 import type { Blake2bHash } from "@typeberry/hash";
-import type {
-  MachineId,
-  MachineResult,
-  MemoryOperation,
-  NoMachineError,
-  PagesError,
-  PeekPokeError,
-  ProgramCounter,
-  RefineExternalities,
+import {
+  type MachineId,
+  type MachineResult,
+  type MemoryOperation,
+  type NoMachineError,
+  type PagesError,
+  type PeekPokeError,
+  type ProgramCounter,
+  type RefineExternalities,
   SegmentExportError,
-  ZeroVoidError,
+  type ZeroVoidError,
 } from "@typeberry/jam-host-calls";
 import type { U64 } from "@typeberry/numbers";
 import type { HostCallMemory, HostCallRegisters } from "@typeberry/pvm-host-calls";
 import type { BigGas } from "@typeberry/pvm-interface";
 import type { ProgramDecoderError } from "@typeberry/pvm-interpreter";
 import type { State } from "@typeberry/state";
-import type { OK, Result } from "@typeberry/utils";
+import { type OK, Result } from "@typeberry/utils";
 
 /**
  * Parameters required to create a RefineExternalitiesImpl.
@@ -28,6 +34,8 @@ export type RefineExternalitiesParams = {
   currentServiceId: ServiceId;
   /** State at the lookup anchor block, used for historical preimage lookups. */
   lookupState: State;
+  /** Export offset -- sum of exports from prior work items in this package. */
+  exportOffset: number;
 };
 
 export class RefineExternalitiesImpl implements RefineExternalities {
@@ -35,6 +43,10 @@ export class RefineExternalitiesImpl implements RefineExternalities {
   private readonly currentServiceId: ServiceId;
   /** State at the lookup anchor for preimage lookups. */
   private readonly lookupState: State;
+  /** Segments exported by this work item during refinement. */
+  private readonly exportedSegments: Segment[] = [];
+  /** Offset for segment indexing (sum of exports from prior items). */
+  private readonly exportOffset: number;
 
   static create(params: RefineExternalitiesParams) {
     return new RefineExternalitiesImpl(params);
@@ -43,6 +55,11 @@ export class RefineExternalitiesImpl implements RefineExternalities {
   private constructor(params: RefineExternalitiesParams) {
     this.currentServiceId = params.currentServiceId;
     this.lookupState = params.lookupState;
+    this.exportOffset = params.exportOffset;
+  }
+
+  getExportedSegments(): readonly Segment[] {
+    return this.exportedSegments;
   }
 
   machineExpunge(_machineIndex: MachineId): Promise<Result<ProgramCounter, NoMachineError>> {
@@ -98,8 +115,19 @@ export class RefineExternalitiesImpl implements RefineExternalities {
     throw new Error("Method not implemented.");
   }
 
-  exportSegment(_segment: Segment): Result<SegmentIndex, SegmentExportError> {
-    throw new Error("Method not implemented.");
+  exportSegment(segment: Segment): Result<SegmentIndex, SegmentExportError> {
+    // https://graypaper.fluffylabs.dev/#/ab2cdbd/335d03335d03?v=0.7.2
+    const currentIndex = this.exportOffset + this.exportedSegments.length;
+    if (currentIndex >= MAX_NUMBER_OF_EXPORTS_WP) {
+      return Result.error(
+        SegmentExportError,
+        () =>
+          `Maximum number of exported segments exceeded (offset: ${this.exportOffset}, exported: ${this.exportedSegments.length})`,
+      );
+    }
+    // https://graypaper.fluffylabs.dev/#/ab2cdbd/337303337303?v=0.7.2
+    this.exportedSegments.push(segment);
+    return Result.ok(tryAsSegmentIndex(currentIndex));
   }
 
   historicalLookup(serviceId: ServiceId | null, hash: Blake2bHash): Promise<BytesBlob | null> {
diff --git a/packages/jam/in-core/in-core.ts b/packages/jam/in-core/in-core.ts
index 594dab7c9..acbde75e6 100644
--- a/packages/jam/in-core/in-core.ts
+++ b/packages/jam/in-core/in-core.ts
@@ -40,7 +40,7 @@ export type RefineResult = {
 
 export type RefineItemResult = {
   result: WorkResult;
-  exports: Segment[];
+  exports: readonly Segment[];
 };
 
 export enum RefineError {
@@ -171,13 +171,24 @@ export class InCore {
     logger.log`[core:${core}] Authorized. Proceeding with work items verification. Anchor=${context.anchor}`;
 
     // Verify the work items
+    let exportOffset = 0;
     const refineResults: Awaited<ReturnType<InCore["refineItem"]>>[] = [];
     for (const [idx, item] of items.entries()) {
       logger.info`[core:${core}][i:${idx}] Refining item for service ${item.service}.`;
 
-      refineResults.push(
-        await this.refineItem(state, lookupState, idx, item, imports, extrinsics, core, workPackageHash),
+      const result = await this.refineItem(
+        state,
+        lookupState,
+        idx,
+        item,
+        imports,
+        extrinsics,
+        core,
+        workPackageHash,
+        exportOffset,
       );
+      refineResults.push(result);
+      exportOffset += result.exports.length;
     }
 
     // amalgamate the work report now
@@ -268,6 +279,7 @@ export class InCore {
     allExtrinsics: PerWorkItem<WorkItemExtrinsic[]>,
     coreIndex: CoreIndex,
     workPackageHash: WorkPackageHash,
+    exportOffset: number,
   ): Promise<RefineItemResult> {
     const payloadHash = this.blake2b.hashBytes(item.payload);
     const baseResult = {
@@ -311,6 +323,7 @@ export class InCore {
       extrinsics: allExtrinsics,
       currentServiceId: item.service,
       lookupState,
+      exportOffset,
     });
 
     const executor = await PvmExecutor.createRefineExecutor(item.service, code, externalities, this.pvmBackend);
@@ -325,8 +338,7 @@ export class InCore {
 
     const execResult = await executor.run(args, item.refineGasLimit);
 
-    // TODO [ToDr] get exports from externalities
-    const exports: Segment[] = [];
+    const exports = externalities.refine.getExportedSegments();
     if (exports.length !== item.exportCount) {
       return {
         exports,
@@ -422,6 +434,7 @@ export class InCore {
     extrinsics: PerWorkItem<WorkItemExtrinsic[]>;
     currentServiceId: ServiceId;
     lookupState: State;
+    exportOffset: number;
   }): RefineHostCallExternalities {
     // TODO [ToDr] Pass all required fetch data
     const fetchExternalities = FetchExternalities.createForRefine(
@@ -434,6 +447,7 @@ export class InCore {
     const refine = RefineExternalitiesImpl.create({
       currentServiceId: args.currentServiceId,
       lookupState: args.lookupState,
+      exportOffset: args.exportOffset,
     });
 
     return {
diff --git a/packages/jam/in-core/package.json b/packages/jam/in-core/package.json
index 73624f265..887a985ce 100644
--- a/packages/jam/in-core/package.json
+++ b/packages/jam/in-core/package.json
@@ -15,6 +15,7 @@
     "@typeberry/database": "*",
     "@typeberry/executor": "*",
     "@typeberry/hash": "*",
+    "@typeberry/jam-host-calls": "*",
     "@typeberry/logger": "*",
     "@typeberry/numbers": "*",
     "@typeberry/state": "*",
diff --git a/packages/jam/jam-host-calls/externalities/refine-externalities.test.ts b/packages/jam/jam-host-calls/externalities/refine-externalities.test.ts
index 58744303a..d53fc0435 100644
--- a/packages/jam/jam-host-calls/externalities/refine-externalities.test.ts
+++ b/packages/jam/jam-host-calls/externalities/refine-externalities.test.ts
@@ -60,6 +60,12 @@ export class TestRefineExt implements RefineExternalities {
 
   public machineInvokeStatus: MachineStatus = { status: Status.OK };
 
+  private readonly exportSegments: Segment[] = [];
+
+  getExportedSegments(): readonly Segment[] {
+    return this.exportSegments;
+  }
+
   machineExpunge(machineIndex: MachineId): Promise<Result<ProgramCounter, NoMachineError>> {
     const val = this.machineExpungeData.get(machineIndex);
     if (val === undefined) {
@@ -151,6 +157,7 @@ export class TestRefineExt implements RefineExternalities {
     if (result === undefined) {
       throw new Error(`Unexpected call to exportSegment with: ${segment}`);
     }
+    this.exportSegments.push(segment);
     return result;
   }
 
diff --git a/packages/jam/jam-host-calls/externalities/refine-externalities.ts b/packages/jam/jam-host-calls/externalities/refine-externalities.ts
index c2e62a78b..bc858b467 100644
--- a/packages/jam/jam-host-calls/externalities/refine-externalities.ts
+++ b/packages/jam/jam-host-calls/externalities/refine-externalities.ts
@@ -107,6 +107,9 @@ export type SegmentExportError = typeof SegmentExportError;
 
 /** Host functions external invocations available during refine phase. */
 export interface RefineExternalities {
+  /** Get the segments exported during this work item's refinement. */
+  getExportedSegments(): readonly Segment[];
+
   /** Forget a previously started nested VM. */
   machineExpunge(machineIndex: MachineId): Promise<Result<ProgramCounter, NoMachineError>>;
 
diff --git a/packages/jam/jam-host-calls/refine/export.test.ts b/packages/jam/jam-host-calls/refine/export.test.ts
index 4e782256d..844ce04e4 100644
--- a/packages/jam/jam-host-calls/refine/export.test.ts
+++ b/packages/jam/jam-host-calls/refine/export.test.ts
@@ -57,6 +57,7 @@ describe("HostCalls: Export", () => {
     // then
     assert.deepStrictEqual(result, undefined);
     assert.deepStrictEqual(registers.get(RESULT_REG), 15n);
+    assert.strictEqual(refine.getExportedSegments().length, 1);
   });
 
   it("should zero-pad when exported value is small", async () => {
@@ -75,6 +76,7 @@ describe("HostCalls: Export", () => {
     // then
     assert.deepStrictEqual(result, undefined);
     assert.deepStrictEqual(registers.get(RESULT_REG), 5n);
+    assert.strictEqual(refine.getExportedSegments().length, 1);
   });
 
   it("should panic if memory is not readable", async () => {
@@ -89,6 +91,7 @@ describe("HostCalls: Export", () => {
 
     // then
     assert.deepStrictEqual(result, PvmExecution.Panic);
+    assert.strictEqual(refine.getExportedSegments().length, 0);
   });
 
   it("should fail with FULL if export limit is reached", async () => {
diff --git a/packages/jam/jam-host-calls/refine/export.ts b/packages/jam/jam-host-calls/refine/export.ts
index 5d9321a9d..30f15cd5b 100644
--- a/packages/jam/jam-host-calls/refine/export.ts
+++ b/packages/jam/jam-host-calls/refine/export.ts
@@ -21,7 +21,7 @@ const IN_OUT_REG = 7;
 /**
  * Export a segment to be imported by some future `refine` invokation.
  *
- * https://graypaper.fluffylabs.dev/#/7e6ff6a/341d01341d01?v=0.6.7
+ * https://graypaper.fluffylabs.dev/#/ab2cdbd/33db0233db02?v=0.7.2
  */
 export class Export implements HostCallHandler {
   index = tryAsHostCallIndex(7);
diff --git a/packages/jam/jam-host-calls/refine/historical-lookup.ts b/packages/jam/jam-host-calls/refine/historical-lookup.ts
index 3c20c6827..f8d6e045e 100644
--- a/packages/jam/jam-host-calls/refine/historical-lookup.ts
+++ b/packages/jam/jam-host-calls/refine/historical-lookup.ts
@@ -20,7 +20,7 @@ const IN_OUT_REG = 7;
 /**
  * Lookup a historical preimage.
  *
- * https://graypaper.fluffylabs.dev/#/7e6ff6a/343b00343b00?v=0.6.7
+ * https://graypaper.fluffylabs.dev/#/ab2cdbd/33c90133c901?v=0.7.2
  */
 export class HistoricalLookup implements HostCallHandler {
   index = tryAsHostCallIndex(6);