diff --git a/.changeset/ambient-slippage-basis-points.md b/.changeset/ambient-slippage-basis-points.md
new file mode 100644
index 000000000..dc6874b17
--- /dev/null
+++ b/.changeset/ambient-slippage-basis-points.md
@@ -0,0 +1,5 @@
+---
+'@sovryn/sdk': patch
+---
+
+Fix Ambient route slippage encoding: `options.slippage` is expressed in basis points (10_000 = 100%) but was divided by 1000 instead of 10000 before being passed to sdex, so the enforced slippage bound was 10x looser than the value the user selected (e.g. 0.5% became 5%). The `?? 50` fallback keeps its intended meaning of 0.5%, matching the UI's preset tolerance.
diff --git a/packages/sdk/src/_tests/swaps/routes/ambient-route.test.ts b/packages/sdk/src/_tests/swaps/routes/ambient-route.test.ts
new file mode 100644
index 000000000..00fffdbf4
--- /dev/null
+++ b/packages/sdk/src/_tests/swaps/routes/ambient-route.test.ts
@@ -0,0 +1,154 @@
+import { BigNumber, constants, providers } from 'ethers';
+
+import { OrderDirective } from '@sovryn/sdex/dist/encoding/longform';
+
+import { getMinReturn } from '../../../internal/utils';
+import { ambientRoute } from '../../../swaps/smart-router/routes/ambient';
+import { SwapRoute } from '../../../swaps/smart-router/types';
+
+const BOB_MAINNET_CHAIN_ID = 60808;
+
+const mockTokenA = '0x00000000000000000000000000000000000000aa';
+const mockTokenB = '0x00000000000000000000000000000000000000bb';
+// sorts below A and B so the second hop of A -> B -> C is a sell leg
+const mockTokenC = '0x0000000000000000000000000000000000000011';
+const mockZeroAddress = '0x0000000000000000000000000000000000000000';
+
+// Q64.64 sqrt price of 1.0, i.e. 2^64
+const mockUnitSqrtPrice = '18446744073709551616';
+
+// pools returned by the mocked indexer; tests may override per case
+let mockPools: [string, string, number][] = [[mockTokenA, mockTokenB, 400]];
+
+// captures the slippage options handed to sdex's CrocEnv swap plans
+const mockCapturedSlippages: number[] = [];
+
+jest.mock('@sovryn/sdex', () => ({
+  CrocEnv: jest.fn().mockImplementation(() => ({
+    context: Promise.resolve({
+      dex: {
+        address: mockZeroAddress,
+        interface: { encodeFunctionData: () => '0x' },
+      },
+      chain: { proxyPaths: { long: 130 } },
+    }),
+    tokens: {
+      materialize: () => ({ decimals: 18 }),
+    },
+    pool: async (tokenA: string, tokenB: string, poolIndex: number) => {
+      const [base, quote] =
+        tokenA < tokenB ? [tokenA, tokenB] : [tokenB, tokenA];
+      return {
+        baseToken: { tokenAddr: base },
+        quoteToken: { tokenAddr: quote },
+        poolIndex,
+      };
+    },
+    sell: () => ({
+      for: (_destination: string, opts: { slippage?: number }) => {
+        if (opts.slippage !== undefined) {
+          mockCapturedSlippages.push(opts.slippage);
+        }
+        return {
+          generateSwapData: async () => ({
+            to: mockZeroAddress,
+            data: '0x',
+            value: '0',
+          }),
+        };
+      },
+    }),
+  })),
+}));
+
+jest.mock('../../../swaps/smart-router/utils/ambient-utils', () => ({
+  ...jest.requireActual('../../../swaps/smart-router/utils/ambient-utils'),
+  fetchPools: async () => mockPools,
+  calcImpact: async () => ({
+    finalPrice: mockUnitSqrtPrice,
+    baseFlow: '1000000000000000000',
+    quoteFlow: '-1000000000000000000',
+  }),
+}));
+
+describe('Ambient route slippage encoding', () => {
+  let route: SwapRoute;
+
+  const provider = {
+    getNetwork: async () => ({ chainId: BOB_MAINNET_CHAIN_ID }),
+  } as providers.Provider;
+
+  const swapWithSlippage = async (slippage?: number) => {
+    mockCapturedSlippages.length = 0;
+    await route.swap(
+      mockTokenA,
+      mockTokenB,
+      constants.WeiPerEther,
+      constants.AddressZero,
+      slippage !== undefined ? { slippage } : undefined,
+    );
+    expect(mockCapturedSlippages).toHaveLength(1);
+    return mockCapturedSlippages[0];
+  };
+
+  beforeEach(() => {
+    mockPools = [[mockTokenA, mockTokenB, 400]];
+    route = ambientRoute(provider);
+  });
+
+  it('encodes basis points as the fraction sdex expects (50 bps -> 0.005)', async () => {
+    const fraction = await swapWithSlippage(50);
+    expect(fraction).toBeCloseTo(0.005, 10);
+  });
+
+  it('defaults to 50 bps (0.5%, the UI preset) when no slippage option is given', async () => {
+    const fraction = await swapWithSlippage();
+    expect(fraction).toBeCloseTo(0.005, 10);
+  });
+
+  it('matches getMinReturn basis-point semantics across tolerance values', async () => {
+    for (const bps of [10, 50, 100, 1000]) {
+      const fraction = await swapWithSlippage(bps);
+
+      const minReturn = getMinReturn(constants.WeiPerEther, bps);
+      const impliedMinReturn = BigNumber.from(
+        BigInt(Math.round((1 - fraction) * 1e18)).toString(),
+      );
+
+      expect(impliedMinReturn.toString()).toEqual(minReturn.toString());
+    }
+  });
+
+  it('bounds each multi-hop pool sqrt price by the same fraction (50 bps -> 1 +/- 0.005)', async () => {
+    mockPools = [
+      [mockTokenA, mockTokenB, 400],
+      [mockTokenC, mockTokenB, 410],
+    ];
+    route = ambientRoute(provider);
+
+    const appendPoolSpy = jest.spyOn(OrderDirective.prototype, 'appendPool');
+
+    // no direct A/C pool -> long-form multi-hop path A -> B -> C
+    await route.swap(
+      mockTokenA,
+      mockTokenC,
+      constants.WeiPerEther,
+      constants.AddressZero,
+      { slippage: 50 },
+    );
+
+    const orderPools = appendPoolSpy.mock.results.map(result => result.value);
+    appendPoolSpy.mockRestore();
+    expect(orderPools).toHaveLength(2);
+
+    // calcImpact is mocked to a sqrt price of exactly 1.0 (2^64), so the
+    // encoded limitPrice ratio is the applied sqrt-price slippage bound
+    const boundRatios = orderPools.map(
+      pool => Number(pool.swap.limitPrice.toString()) / 2 ** 64,
+    );
+
+    // first hop buys (entry is base), second hop sells (entry is quote)
+    expect(boundRatios[0]).toBeCloseTo(1.005, 6);
+    expect(boundRatios[1]).toBeCloseTo(0.995, 6);
+  });
+});
diff --git a/packages/sdk/src/swaps/smart-router/routes/ambient.ts b/packages/sdk/src/swaps/smart-router/routes/ambient.ts
index fb5f2a999..270c2a75b 100644
--- a/packages/sdk/src/swaps/smart-router/routes/ambient.ts
+++ b/packages/sdk/src/swaps/smart-router/routes/ambient.ts
@@ -230,7 +230,9 @@ export const ambientRoute: SwapRouteFunction = (
     },
     permit: async () => Promise.resolve(undefined),
     swap: async (entry, destination, amount, from, options, overrides) => {
-      const slippage = Number(options?.slippage ?? 50) / 1000;
+      // options.slippage is in basis points (10_000 = 100%); sdex expects a
+      // fraction. Fallback 50 bps = 0.5%, the UI's preset tolerance.
+      const slippage = Number(options?.slippage ?? 50) / 10000;
 
       const pools = await loadPools();
       const chainId = await getChainId();