diff --git a/src/SignalR/clients/ts/signalr/src/AccessTokenHttpClient.ts b/src/SignalR/clients/ts/signalr/src/AccessTokenHttpClient.ts
index e28c98862af6..1abeb0831cf6 100644
--- a/src/SignalR/clients/ts/signalr/src/AccessTokenHttpClient.ts
+++ b/src/SignalR/clients/ts/signalr/src/AccessTokenHttpClient.ts
@@ -1,12 +1,12 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
-import { HeaderNames } from "./HeaderNames";
+// Removed HeaderNames import to reduce bundle size; using literal key.
 import { HttpClient, HttpRequest, HttpResponse } from "./HttpClient";
 
 /** @private */
 export class AccessTokenHttpClient extends HttpClient {
-    private _innerClient: HttpClient;
+    private readonly _innerClient: HttpClient;
     _accessToken: string | undefined;
     _accessTokenFactory: (() => string | Promise<string>) | undefined;
 
@@ -18,36 +18,38 @@ export class AccessTokenHttpClient extends HttpClient {
     }
 
     public async send(request: HttpRequest): Promise<HttpResponse> {
-        let allowRetry = true;
-        if (this._accessTokenFactory && (!this._accessToken || (request.url && request.url.indexOf("/negotiate?") > 0))) {
-            // don't retry if the request is a negotiate or if we just got a potentially new token from the access token factory
-            allowRetry = false;
-            this._accessToken = await this._accessTokenFactory();
-        }
+        const needsToken = !!(this._accessTokenFactory && (!this._accessToken || (request.url && request.url.indexOf('/negotiate?') > 0)));
+        const retry = !needsToken;
+        if (needsToken) this._accessToken = await this._accessTokenFactory!();
         this._setAuthorizationHeader(request);
-        const response = await this._innerClient.send(request);
+        try {
+            const r = await this._innerClient.send(request);
+            return (retry && this._accessTokenFactory && r.statusCode === 401) ? this._refreshTokenAndRetry(request, r) : r;
+        } catch (err: unknown) {
+            if (!retry || !this._accessTokenFactory) throw err;
+            const e = err as any, s = +(e.statusCode ?? e.status);
+            if (s === 401) return this._refreshTokenAndRetry(request, e);
+            throw err;
+        }
+    }
 
-        if (allowRetry && response.statusCode === 401 && this._accessTokenFactory) {
-            this._accessToken = await this._accessTokenFactory();
-            this._setAuthorizationHeader(request);
-            return await this._innerClient.send(request);
+    private async _refreshTokenAndRetry(request: HttpRequest, o: HttpResponse | Error): Promise<HttpResponse> {
+        const t = await this._accessTokenFactory!();
+        if (!t) {
+            this._accessToken = undefined;
+            if (request.headers) delete (request.headers as any).Authorization;
+            if (request.abortSignal) return this._innerClient.send(request);
+            if (o instanceof HttpResponse) return o;
+            return Promise.reject(o);
         }
-        return response;
+        this._accessToken = t;
+        this._setAuthorizationHeader(request);
+        return this._innerClient.send(request);
     }
 
     private _setAuthorizationHeader(request: HttpRequest) {
-        if (!request.headers) {
-            request.headers = {};
-        }
-        if (this._accessToken) {
-            request.headers[HeaderNames.Authorization] = `Bearer ${this._accessToken}`
-        }
-        // don't remove the header if there isn't an access token factory, the user manually added the header in this case
-        else if (this._accessTokenFactory) {
-            if (request.headers[HeaderNames.Authorization]) {
-                delete request.headers[HeaderNames.Authorization];
-            }
-        }
+        const h = request.headers || (request.headers = {});
+        if (this._accessToken) h.Authorization = 'Bearer ' + this._accessToken; else if (this._accessTokenFactory) delete h.Authorization;
     }
 
     public getCookieString(url: string): string {
diff --git a/src/SignalR/clients/ts/signalr/tests/AccessTokenHttpClient.test.ts b/src/SignalR/clients/ts/signalr/tests/AccessTokenHttpClient.test.ts
new file mode 100644
index 000000000000..62f12910a1da
--- /dev/null
+++ b/src/SignalR/clients/ts/signalr/tests/AccessTokenHttpClient.test.ts
@@ -0,0 +1,247 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+import { AccessTokenHttpClient } from "../src/AccessTokenHttpClient";
+import { HttpError } from "../src/Errors";
+import { HttpRequest, HttpResponse } from "../src/HttpClient";
+import { TestHttpClient } from "./TestHttpClient";
+import { registerUnhandledRejectionHandler } from "./Utils";
+import { VerifyLogger } from "./Common";
+import { LongPollingTransport } from "../src/LongPollingTransport";
+import { TransferFormat } from "../src/ITransport";
+
+describe("AccessTokenHttpClient", () => {
+    beforeAll(() => {
+        registerUnhandledRejectionHandler();
+    });
+
+    afterAll(() => {
+        // Optional cleanup could go here.
+    });
+
+    it("retries exactly once on 401 HttpError when accessTokenFactory provided", async () => {
+        let call = 0;
+        let primed = false;
+        const inner = new TestHttpClient();
+        inner.on(() => {
+            if (!primed) {
+                primed = true; // prime request returns 200 and sets initial token
+                return new HttpResponse(200, "OK", "prime");
+            }
+            call++;
+            if (call === 1) {
+                throw new HttpError("Unauthorized", 401);
+            }
+            return new HttpResponse(200, "OK", "done");
+        });
+
+        let factoryCalls = 0;
+        const client = new AccessTokenHttpClient(inner, () => {
+            factoryCalls++;
+            return `token${factoryCalls}`;
+        });
+
+        // Prime token via public API
+        await client.get("http://example.com/prime");
+
+        const response = await client.get("http://example.com/resource");
+        expect(response.statusCode).toBe(200);
+        expect(factoryCalls).toBe(2); // prime + retry refresh
+        expect(call).toBe(2); // failing attempt + successful retry
+    });
+
+    [403, 500].forEach(status => {
+        it(`does not retry on status ${status} HttpError`, async () => {
+            let primed = false;
+            let failingCalls = 0;
+            const inner = new TestHttpClient();
+            inner.on(() => {
+                if (!primed) {
+                    primed = true;
+                    return new HttpResponse(200, "OK", "prime");
+                }
+                failingCalls++;
+                throw new HttpError("Error", status);
+            });
+
+            let factoryCalls = 0;
+            const client = new AccessTokenHttpClient(inner, () => {
+                factoryCalls++;
+                return `token${factoryCalls}`;
+            });
+
+            await client.get("http://example.com/prime");
+            try {
+                await expect(client.get("http://example.com/resource")).rejects.toThrow(HttpError);
+            } catch (e: any) {
+                expect(e).toBeInstanceOf(HttpError);
+                expect(e.statusCode ?? e.status).toBe(status);
+            }
+            expect(factoryCalls).toBe(1);
+            expect(failingCalls).toBe(1);
+        });
+    });
+
+    it("LongPollingTransport continues running after 401 during poll and refreshes token", async () => {
+        await VerifyLogger.run(async (logger) => {
+            let pollIteration = 0;
+            let primed = false;
+            const tokens: string[] = [];
+            const accessTokenFactory = () => {
+                const t = `tok${tokens.length + 1}`;
+                tokens.push(t);
+                return t;
+            };
+            const httpClient = new AccessTokenHttpClient(new TestHttpClient()
+                .on("GET", (r: HttpRequest) => {
+                    // Prime request separate from polling loop
+                    if (!primed && r.url!.includes("/prime")) {
+                        primed = true;
+                        return new HttpResponse(200, "OK", "prime");
+                    }
+                    pollIteration++;
+                    if (pollIteration === 1) { // initial connect poll
+                        return new HttpResponse(200, "OK", "");
+                    }
+                    if (pollIteration === 2) { // trigger 401 -> retry
+                        return new HttpResponse(401);
+                    }
+                    if (pollIteration === 3) { // post-refresh poll
+                        expect(r.headers).toBeDefined();
+                        expect(r.headers?.Authorization).toBeDefined();
+                        expect(r.headers?.Authorization).toContain(tokens[tokens.length - 1]);
+                        return new HttpResponse(204);
+                    }
+                    return new HttpResponse(204);
+                }), accessTokenFactory);
+
+            // Prime token using public API
+            await httpClient.get("http://example.com/prime");
+
+            const transport = new LongPollingTransport(httpClient, logger, { withCredentials: true, headers: {}, logMessageContent: false });
+            await transport.connect("http://example.com?connectionId=abc", TransferFormat.Text);
+            await transport.stop();
+
+            expect(tokens.length).toBe(2); // primed + refreshed
+            expect(pollIteration).toBeGreaterThanOrEqual(3);
+        });
+    });
+
+    it("retries once on 401 HttpResponse status (non-throwing path)", async () => {
+        let primed = false;
+        let attempts = 0;
+        let retryAuthHeader: string | undefined;
+        const inner = new TestHttpClient();
+        inner.on((r: HttpRequest) => {
+            if (!primed && r.url!.includes("/prime")) {
+                primed = true;
+                return new HttpResponse(200, "OK", "prime");
+            }
+            attempts++;
+            if (attempts === 1) {
+                return new HttpResponse(401);
+            }
+            // second attempt after refresh
+            retryAuthHeader = r.headers?.Authorization;
+            return new HttpResponse(200, "OK", "after-retry");
+        });
+
+        let factoryCalls = 0;
+        const client = new AccessTokenHttpClient(inner, () => {
+            factoryCalls++;
+            return `token${factoryCalls}`;
+        });
+
+        await client.get("http://example.com/prime");
+        const resp = await client.get("http://example.com/resource");
+        expect(resp.statusCode).toBe(200);
+        expect(factoryCalls).toBe(2); // prime + refresh
+        expect(attempts).toBe(2); // original 401 + retry 200
+        expect(retryAuthHeader).toContain("token2");
+    });
+
+    it("does not retry when allowRetry is false (initial token acquisition)", async () => {
+        let sends = 0;
+        const inner = new TestHttpClient();
+        inner.on(() => {
+            sends++;
+            return new HttpResponse(401);
+        });
+
+        let factoryCalls = 0;
+        const client = new AccessTokenHttpClient(inner, () => {
+            factoryCalls++;
+            return `token${factoryCalls}`; // Token factory returns a token string for each call.
+        });
+
+        const request: HttpRequest = { method: "GET", url: "http://example.com/resource" };
+        const resp = await client.send(request); // send path with existing logic; allowRetry=false triggered by initial token acquisition above
+        expect(resp.statusCode).toBe(401);
+        expect(factoryCalls).toBe(1);
+        expect(sends).toBe(1);
+    });
+
+    it("does not retry when refreshed token is empty", async () => {
+        let primed = false;
+        let attempts = 0;
+        const inner = new TestHttpClient();
+        inner.on((r: HttpRequest) => {
+            if (!primed && r.url!.includes("/prime")) {
+                primed = true;
+                return new HttpResponse(200, "OK", "prime");
+            }
+            attempts++;
+            return new HttpResponse(401); // cause retry path
+        });
+
+        let factoryCalls = 0;
+        const client = new AccessTokenHttpClient(inner, () => {
+            factoryCalls++;
+            if (factoryCalls === 1) {
+                return "tok1"; // prime
+            }
+            return ""; // refresh returns empty -> should not retry send again
+        });
+
+        await client.get("http://example.com/prime");
+        const resp = await client.get("http://example.com/resource");
+        expect(resp.statusCode).toBe(401); // original response returned
+        expect(factoryCalls).toBe(2); // prime + attempted refresh
+        expect(attempts).toBe(1); // no second send
+    });
+
+    it("retries once when HttpError.status is string '401'", async () => {
+        let primed = false;
+        let attempt = 0;
+        let retryAuth: string | undefined;
+        const inner = new TestHttpClient();
+        inner.on((r: HttpRequest) => {
+            if (!primed && r.url!.includes("/prime")) {
+                primed = true;
+                return new HttpResponse(200, "OK", "prime");
+            }
+            attempt++;
+            if (attempt === 1) {
+                const err: any = new Error("Unauthorized: Status code '401'");
+                err.name = "HttpError"; // mimic HttpError shape without statusCode
+                err.status = "401"; // string status to trigger normalization path
+                throw err;
+            }
+            retryAuth = r.headers?.Authorization;
+            return new HttpResponse(200, "OK", "ok");
+        });
+
+        let factoryCalls = 0;
+        const client = new AccessTokenHttpClient(inner, () => {
+            factoryCalls++;
+            return `token${factoryCalls}`;
+        });
+
+        await client.get("http://example.com/prime");
+        const resp = await client.get("http://example.com/resource");
+        expect(resp.statusCode).toBe(200);
+        expect(factoryCalls).toBe(2); // prime + refresh after string status retry
+        expect(attempt).toBe(2); // original throw + retry
+        expect(retryAuth).toContain("token2");
+    });
+});