diff --git a/core/src/exchanges/hyperliquid/index.ts b/core/src/exchanges/hyperliquid/index.ts
index f5d0fa37..0c05eed7 100644
--- a/core/src/exchanges/hyperliquid/index.ts
+++ b/core/src/exchanges/hyperliquid/index.ts
@@ -250,13 +250,27 @@ export class HyperliquidExchange extends PredictionMarketExchange {
                 : { limit: { tif: 'Gtc' } },
         };
 
-        // Key order matters for msgpack hash: type, orders, grouping
+        // Key order matters for msgpack hash: type, orders, grouping, builder
         const action: Record<string, unknown> = {
             type: 'order',
             orders: [orderWire],
             grouping: 'na',
         };
 
+        if (params.builder !== undefined || params.builderFee !== undefined) {
+            if (!params.builder) {
+                throw new Error('Hyperliquid builderFee requires builder address');
+            }
+            if (!/^0x[0-9a-fA-F]{40}$/.test(params.builder)) {
+                throw new Error(`Invalid Hyperliquid builder address: ${params.builder}`);
+            }
+            const builderFee = params.builderFee ?? 0;
+            if (!Number.isInteger(builderFee) || builderFee < 0) {
+                throw new Error('Hyperliquid builderFee must be a non-negative integer in tenths of a basis point');
+            }
+            action.builder = { b: params.builder.toLowerCase(), f: builderFee };
+        }
+
         return {
             exchange: this.name,
             params,
diff --git a/core/src/server/openapi.yaml b/core/src/server/openapi.yaml
index 428cf7d9..45cb13aa 100644
--- a/core/src/server/openapi.yaml
+++ b/core/src/server/openapi.yaml
@@ -3992,6 +3992,12 @@ components:
         fee:
           type: number
           description: 'Optional fee rate (e.g., 1000 for 0.1%)'
+        builder:
+          type: string
+          description: Hyperliquid builder address to attach to the order action.
+        builderFee:
+          type: number
+          description: Hyperliquid builder fee in tenths of a basis point (e.g. 10 = 1 bp).
         tickSize:
           type: number
           description: Optional override for Limitless/Polymarket
diff --git a/core/src/types.ts b/core/src/types.ts
index eb122413..b8df178b 100644
--- a/core/src/types.ts
+++ b/core/src/types.ts
@@ -326,6 +326,10 @@ export interface CreateOrderParams {
     denom?: 'usdc' | 'shares'; // Hosted mode: amount unit.
     slippage_pct?: number; // Hosted mode: maximum market-order slippage percentage.
     fee?: number;   // Optional fee rate (e.g., 1000 for 0.1%)
+    /** Hyperliquid builder address to attach to the order action. */
+    builder?: string;
+    /** Hyperliquid builder fee in tenths of a basis point (e.g. 10 = 1 bp). */
+    builderFee?: number;
     tickSize?: number; // Optional override for Limitless/Polymarket
     negRisk?: boolean; // Optional override to skip neg-risk lookup (Polymarket)
     onBehalfOf?: number; // Limitless delegated signing: profile ID to trade on behalf of
diff --git a/core/test/exchanges/hyperliquid-build-order.test.ts b/core/test/exchanges/hyperliquid-build-order.test.ts
new file mode 100644
index 00000000..6d756627
--- /dev/null
+++ b/core/test/exchanges/hyperliquid-build-order.test.ts
@@ -0,0 +1,54 @@
+import { HyperliquidExchange } from '../../src/exchanges/hyperliquid';
+
+describe('HyperliquidExchange buildOrder builder attribution', () => {
+    const params = {
+        marketId: 'hl:#100001751',
+        outcomeId: '100001751',
+        side: 'buy' as const,
+        type: 'limit' as const,
+        amount: 10,
+        price: 0.001,
+    };
+
+    it('attaches builder attribution when builder params are supplied', async () => {
+        const exchange = new HyperliquidExchange({ testnet: true });
+        const built = await exchange.buildOrder({
+            ...params,
+            builder: '0x370a6D37911294ebE8D45419d007E7e0C4BEC2a9',
+            builderFee: 10,
+        });
+
+        expect(built.raw).toEqual({
+            type: 'order',
+            orders: [{
+                a: 100001751,
+                b: true,
+                p: '0.001',
+                s: '10',
+                r: false,
+                t: { limit: { tif: 'Gtc' } },
+            }],
+            grouping: 'na',
+            builder: {
+                b: '0x370a6d37911294ebe8d45419d007e7e0c4bec2a9',
+                f: 10,
+            },
+        });
+    });
+
+    it('rejects malformed builder params before signing', async () => {
+        const exchange = new HyperliquidExchange({ testnet: true });
+
+        await expect(exchange.buildOrder({ ...params, builderFee: 10 })).rejects.toThrow(
+            'Hyperliquid builderFee requires builder address',
+        );
+        await expect(exchange.buildOrder({ ...params, builder: '0x123', builderFee: 10 })).rejects.toThrow(
+            'Invalid Hyperliquid builder address',
+        );
+        await expect(exchange.buildOrder({
+            ...params,
+            builder: '0x370a6D37911294ebE8D45419d007E7e0C4BEC2a9',
+            builderFee: 0.5,
+        })).rejects.toThrow('Hyperliquid builderFee must be a non-negative integer');
+    });
+});
diff --git a/docs/api-reference/openapi.json b/docs/api-reference/openapi.json
index 72ee155e..e0d7d3d9 100644
--- a/docs/api-reference/openapi.json
+++ b/docs/api-reference/openapi.json
@@ -9909,6 +9909,14 @@
             "type": "number",
             "description": "Optional fee rate (e.g., 1000 for 0.1%)"
           },
+          "builder": {
+            "type": "string",
+            "description": "Hyperliquid builder address to attach to the order action."
+          },
+          "builderFee": {
+            "type": "number",
+            "description": "Hyperliquid builder fee in tenths of a basis point (e.g. 10 = 1 bp)."
+          },
           "tickSize": {
             "type": "number",
             "description": "Optional override for Limitless/Polymarket"
diff --git a/sdks/python/API_REFERENCE.md b/sdks/python/API_REFERENCE.md
index 44a18595..eabcd275 100644
--- a/sdks/python/API_REFERENCE.md
+++ b/sdks/python/API_REFERENCE.md
@@ -2274,6 +2274,8 @@ price: float # Required for limit orders
 denom: str # Hosted mode: amount unit.
 slippage_pct: float # Hosted mode: maximum market-order slippage percentage.
 fee: float # Optional fee rate (e.g., 1000 for 0.1%)
+builder: str # Hyperliquid builder address to attach to the order action.
+builder_fee: float # Hyperliquid builder fee in tenths of a basis point (e.g. 10 = 1 bp).
 tick_size: float # Optional override for Limitless/Polymarket
 neg_risk: bool # Optional override to skip neg-risk lookup (Polymarket)
 on_behalf_of: float # Limitless delegated signing: profile ID to trade on behalf of
diff --git a/sdks/typescript/API_REFERENCE.md b/sdks/typescript/API_REFERENCE.md
index 79ec1a85..bbe5a1fe 100644
--- a/sdks/typescript/API_REFERENCE.md
+++ b/sdks/typescript/API_REFERENCE.md
@@ -2269,6 +2269,8 @@ price?: number; // Required for limit orders
 denom?: string; // Hosted mode: amount unit.
 slippage_pct?: number; // Hosted mode: maximum market-order slippage percentage.
 fee?: number; // Optional fee rate (e.g., 1000 for 0.1%)
+builder?: string; // Hyperliquid builder address to attach to the order action.
+builderFee?: number; // Hyperliquid builder fee in tenths of a basis point (e.g. 10 = 1 bp).
 tickSize?: number; // Optional override for Limitless/Polymarket
 negRisk?: boolean; // Optional override to skip neg-risk lookup (Polymarket)
 onBehalfOf?: number; // Limitless delegated signing: profile ID to trade on behalf of