diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index d872548..0853019 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -38,3 +38,36 @@ jobs:
 
       - name: Run tests
         run: npm test
+
+  deno:
+    # Deno (and other WinterCG runtimes) validate `RequestInit` strictly, so
+    # bugs that leak internal SDK fields into `new Request(...)` are invisible
+    # to the Node test suite but break every call on Deno Deploy / Supabase
+    # Edge Functions. This job runs a real SDK call (stubbed fetch, no network)
+    # against the built bundle under Deno.
+    name: Deno smoke test
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v4
+
+      - name: Setup Node.js
+        uses: actions/setup-node@v4
+        with:
+          node-version: '20'
+          cache: 'npm'
+
+      - name: Install dependencies
+        run: npm ci
+
+      - name: Build SDK
+        run: npm run build
+
+      - name: Setup Deno
+        uses: denoland/setup-deno@v2
+        with:
+          deno-version: v2.x
+
+      - name: Run Deno smoke test
+        run: npm run test:deno
diff --git a/package.json b/package.json
index 7454208..6df9ddb 100644
--- a/package.json
+++ b/package.json
@@ -33,6 +33,7 @@
     "typecheck": "tsc --noEmit",
     "test": "vitest run",
     "test:watch": "vitest",
+    "test:deno": "deno test --allow-read --allow-env tests/deno/smoke.ts",
     "prepublishOnly": "npm run build",
     "fetch-spec": "curl -o openapi.yaml https://zernio.com/openapi.yaml"
   },
diff --git a/scripts/generate-client.ts b/scripts/generate-client.ts
index 21613bd..35b2ed4 100644
--- a/scripts/generate-client.ts
+++ b/scripts/generate-client.ts
@@ -338,6 +338,13 @@ export class Zernio {
    */
   private _client!: Client;
 
+  /**
+   * Wrapper around \`_client\` that \`_bind\` injects into operations. Identical
+   * to \`_client\` except that its HTTP methods strip the \`client\` selector from
+   * request options before dispatch (see \`_stripClientSelector\`).
+   */
+  private _dispatchClient!: Client;
+
   /**
    * API key used for authentication.
    */
@@ -358,12 +365,56 @@ export class Zernio {
     return ((options?: Record<string, unknown>) => {
       const withClient = { ...options };
       if (withClient['client'] === undefined) {
-        withClient['client'] = this._client;
+        withClient['client'] = this._dispatchClient;
       }
       return (operation as (opts: unknown) => unknown)(withClient);
     }) as F;
   }
 
+  /**
+   * TODO: remove once hey-api ships a fix for
+   * https://github.com/hey-api/hey-api/issues/4177 and we can upgrade.
+   *
+   * \`_bind\` injects the per-instance client into each operation's options
+   * under the \`client\` key, and the generated operations forward that whole
+   * options object to @hey-api/client-fetch, which spreads it into the fetch
+   * \`RequestInit\`. Node's undici ignores unknown init fields, but Deno defines
+   * its own \`client\` init option (a \`Deno.HttpClient\`) and validates it, so
+   * \`new Request(...)\` throws and every SDK call fails on Deno, Deno Deploy,
+   * and Supabase Edge Functions. The selector has already done its job by the
+   * time an HTTP method runs, so this wrapper strips it before hey-api builds
+   * the request. The real client is left untouched — config and interceptors
+   * still live on it, and the wrapper delegates everything else to it.
+   */
+  private static _stripClientSelector(client: Client): Client {
+    const wrapped = Object.create(client) as Client;
+    const methods = [
+      'connect',
+      'delete',
+      'get',
+      'head',
+      'options',
+      'patch',
+      'post',
+      'put',
+      'trace',
+    ] as const;
+    for (const method of methods) {
+      const dispatch = client[method] as (requestOptions?: unknown) => unknown;
+      (wrapped as unknown as Record<string, unknown>)[method] = (
+        requestOptions?: Record<string, unknown>
+      ) => {
+        if (requestOptions && 'client' in requestOptions) {
+          const sanitized = { ...requestOptions };
+          delete sanitized['client'];
+          return dispatch(sanitized);
+        }
+        return dispatch(requestOptions);
+      };
+    }
+    return wrapped;
+  }
+
 ${namespaceProps.join('\n\n')}
 
   /**
@@ -405,6 +456,11 @@ ${namespaceProps.join('\n\n')}
       })
     );
 
+    // Deno / WinterCG compatibility: operations dispatch through a wrapper
+    // that strips the \`client\` selector from request options (see
+    // \`_stripClientSelector\`).
+    this._dispatchClient = Zernio._stripClientSelector(this._client);
+
     // Add auth interceptor
     this._client.interceptors.request.use((request) => {
       request.headers.set('Authorization', \`Bearer \${this.apiKey}\`);
diff --git a/src/client.ts b/src/client.ts
index 829252f..5af5b27 100644
--- a/src/client.ts
+++ b/src/client.ts
@@ -613,6 +613,13 @@ export class Zernio {
    */
   private _client!: Client;
 
+  /**
+   * Wrapper around `_client` that `_bind` injects into operations. Identical
+   * to `_client` except that its HTTP methods strip the `client` selector from
+   * request options before dispatch (see `_stripClientSelector`).
+   */
+  private _dispatchClient!: Client;
+
   /**
    * API key used for authentication.
    */
@@ -633,12 +640,56 @@ export class Zernio {
     return ((options?: Record<string, unknown>) => {
       const withClient = { ...options };
       if (withClient['client'] === undefined) {
-        withClient['client'] = this._client;
+        withClient['client'] = this._dispatchClient;
       }
       return (operation as (opts: unknown) => unknown)(withClient);
     }) as F;
   }
 
+  /**
+   * TODO: remove once hey-api ships a fix for
+   * https://github.com/hey-api/hey-api/issues/4177 and we can upgrade.
+   *
+   * `_bind` injects the per-instance client into each operation's options
+   * under the `client` key, and the generated operations forward that whole
+   * options object to @hey-api/client-fetch, which spreads it into the fetch
+   * `RequestInit`. Node's undici ignores unknown init fields, but Deno defines
+   * its own `client` init option (a `Deno.HttpClient`) and validates it, so
+   * `new Request(...)` throws and every SDK call fails on Deno, Deno Deploy,
+   * and Supabase Edge Functions. The selector has already done its job by the
+   * time an HTTP method runs, so this wrapper strips it before hey-api builds
+   * the request. The real client is left untouched — config and interceptors
+   * still live on it, and the wrapper delegates everything else to it.
+   */
+  private static _stripClientSelector(client: Client): Client {
+    const wrapped = Object.create(client) as Client;
+    const methods = [
+      'connect',
+      'delete',
+      'get',
+      'head',
+      'options',
+      'patch',
+      'post',
+      'put',
+      'trace',
+    ] as const;
+    for (const method of methods) {
+      const dispatch = client[method] as (requestOptions?: unknown) => unknown;
+      (wrapped as unknown as Record<string, unknown>)[method] = (
+        requestOptions?: Record<string, unknown>
+      ) => {
+        if (requestOptions && 'client' in requestOptions) {
+          const sanitized = { ...requestOptions };
+          delete sanitized['client'];
+          return dispatch(sanitized);
+        }
+        return dispatch(requestOptions);
+      };
+    }
+    return wrapped;
+  }
+
   /**
    * validate API
    */
@@ -1839,6 +1890,11 @@ export class Zernio {
       })
     );
 
+    // Deno / WinterCG compatibility: operations dispatch through a wrapper
+    // that strips the `client` selector from request options (see
+    // `_stripClientSelector`).
+    this._dispatchClient = Zernio._stripClientSelector(this._client);
+
     // Add auth interceptor
     this._client.interceptors.request.use((request) => {
       request.headers.set('Authorization', `Bearer ${this.apiKey}`);
diff --git a/tests/deno/smoke.ts b/tests/deno/smoke.ts
new file mode 100644
index 0000000..d7d85a4
--- /dev/null
+++ b/tests/deno/smoke.ts
@@ -0,0 +1,72 @@
+/**
+ * Deno smoke test for the built SDK bundle. Run with:
+ *
+ *   npm run build && npm run test:deno
+ *
+ * Deno (and other WinterCG runtimes) validate `RequestInit` strictly, so bugs
+ * that leak internal SDK fields into `new Request(...)` are invisible on Node
+ * but fatal here — see https://github.com/hey-api/hey-api/issues/4177 and the
+ * `_stripClientSelector` workaround in src/client.ts. Every request in this
+ * file goes through a stubbed `fetch`; no network I/O and no real credentials.
+ *
+ * This file deliberately avoids a `.test.ts` suffix so vitest's default glob
+ * ignores it; `deno test` runs it by explicit path.
+ */
+import Zernio from '../../dist/index.mjs';
+
+function assert(condition: unknown, message: string): asserts condition {
+  if (!condition) {
+    throw new Error(message);
+  }
+}
+
+function stubFetch(onRequest?: (request: Request) => void): void {
+  globalThis.fetch = ((input: Request | URL | string) => {
+    onRequest?.(input as Request);
+    return Promise.resolve(
+      new Response(JSON.stringify({ accounts: [] }), {
+        status: 200,
+        headers: { 'content-type': 'application/json' },
+      })
+    );
+  }) as typeof fetch;
+}
+
+Deno.test('SDK call constructs a valid Request under Deno', async () => {
+  stubFetch();
+  const client = new Zernio({ apiKey: 'sk_deno_ci' });
+
+  // Before the _stripClientSelector fix this threw at `new Request(...)` with
+  // "Argument 2 `client` must be a Deno.HttpClient", before fetch was reached.
+  const result = await client.accounts.listAccounts({});
+
+  assert(result.response?.status === 200, 'expected a 200 from the stubbed fetch');
+});
+
+Deno.test('auth header is applied through the per-instance client', async () => {
+  const authHeaders: (string | null)[] = [];
+  stubFetch((request) => authHeaders.push(request.headers.get('Authorization')));
+
+  const client = new Zernio({ apiKey: 'sk_deno_ci' });
+  await client.accounts.listAccounts({});
+
+  assert(authHeaders.length === 1, 'expected exactly one request');
+  assert(authHeaders[0] === 'Bearer sk_deno_ci', `unexpected auth header: ${authHeaders[0]}`);
+});
+
+Deno.test('two instances keep their own credentials', async () => {
+  const authHeaders: (string | null)[] = [];
+  stubFetch((request) => authHeaders.push(request.headers.get('Authorization')));
+
+  const first = new Zernio({ apiKey: 'sk_FIRST' });
+  const second = new Zernio({ apiKey: 'sk_SECOND' });
+  await first.accounts.listAccounts({});
+  await second.accounts.listAccounts({});
+  await first.accounts.listAccounts({});
+
+  assert(
+    JSON.stringify(authHeaders) ===
+      JSON.stringify(['Bearer sk_FIRST', 'Bearer sk_SECOND', 'Bearer sk_FIRST']),
+    `instances leaked credentials: ${JSON.stringify(authHeaders)}`
+  );
+});
diff --git a/tests/request-init.test.ts b/tests/request-init.test.ts
new file mode 100644
index 0000000..05bba75
--- /dev/null
+++ b/tests/request-init.test.ts
@@ -0,0 +1,79 @@
+import { describe, it, expect, beforeEach, afterEach, vi } from 'vitest';
+import Zernio from '../src';
+
+/**
+ * `_bind` injects the per-instance client into each operation's options under
+ * the `client` key, and @hey-api/client-fetch spreads the whole per-request
+ * options object into the fetch `RequestInit`. Node's undici ignores unknown
+ * init fields, but Deno defines its own `client` init option (a
+ * `Deno.HttpClient`) and validates it, so `new Request(...)` throws and every
+ * SDK call fails on Deno, Deno Deploy, and Supabase Edge Functions
+ * (hey-api upstream: https://github.com/hey-api/hey-api/issues/4177).
+ *
+ * These tests run under Node, so they capture the init at `new Request` time —
+ * undici would otherwise silently swallow the stray field and hide the bug.
+ */
+describe('request construction (Deno / WinterCG compatibility)', () => {
+  const OriginalRequest = globalThis.Request;
+  const originalFetch = globalThis.fetch;
+  let capturedInits: (RequestInit | undefined)[];
+
+  beforeEach(() => {
+    capturedInits = [];
+    globalThis.Request = class extends OriginalRequest {
+      constructor(input: RequestInfo | URL, init?: RequestInit) {
+        capturedInits.push(init);
+        super(input, init);
+      }
+    } as unknown as typeof Request;
+    globalThis.fetch = vi.fn(
+      async () =>
+        new Response('{}', { status: 200, headers: { 'content-type': 'application/json' } })
+    ) as unknown as typeof fetch;
+  });
+
+  afterEach(() => {
+    globalThis.Request = OriginalRequest;
+    globalThis.fetch = originalFetch;
+  });
+
+  it('never leaks the client selector into the fetch RequestInit', async () => {
+    const client = new Zernio({ apiKey: 'sk_test' });
+
+    await client.accounts.listAccounts({});
+
+    expect(capturedInits.length).toBeGreaterThan(0);
+    for (const init of capturedInits) {
+      expect(init && 'client' in init).toBe(false);
+    }
+  });
+
+  it('still routes through the per-instance client (auth header is applied)', async () => {
+    const authHeaders: (string | null)[] = [];
+    globalThis.fetch = vi.fn(async (input: RequestInfo | URL) => {
+      authHeaders.push((input as Request).headers.get('Authorization'));
+      return new Response('{}', { status: 200, headers: { 'content-type': 'application/json' } });
+    }) as unknown as typeof fetch;
+
+    const client = new Zernio({ apiKey: 'sk_ABCD' });
+    await client.accounts.listAccounts({});
+
+    expect(authHeaders).toEqual(['Bearer sk_ABCD']);
+  });
+
+  it('keeps per-instance isolation between two clients', async () => {
+    const authHeaders: (string | null)[] = [];
+    globalThis.fetch = vi.fn(async (input: RequestInfo | URL) => {
+      authHeaders.push((input as Request).headers.get('Authorization'));
+      return new Response('{}', { status: 200, headers: { 'content-type': 'application/json' } });
+    }) as unknown as typeof fetch;
+
+    const first = new Zernio({ apiKey: 'sk_FIRST' });
+    const second = new Zernio({ apiKey: 'sk_SECOND' });
+    await first.accounts.listAccounts({});
+    await second.accounts.listAccounts({});
+    await first.accounts.listAccounts({});
+
+    expect(authHeaders).toEqual(['Bearer sk_FIRST', 'Bearer sk_SECOND', 'Bearer sk_FIRST']);
+  });
+});