diff --git a/.changeset/envvars-update-outside-task.md b/.changeset/envvars-update-outside-task.md
new file mode 100644
index 00000000000..19afdd86a8b
--- /dev/null
+++ b/.changeset/envvars-update-outside-task.md
@@ -0,0 +1,5 @@
+---
+"@trigger.dev/sdk": patch
+---
+
+`envvars.update()`: calling it outside a task run no longer throws `ReferenceError: name is not defined`. The variable name is now resolved from the positional arguments, matching the other env var methods, and a missing name raises a descriptive `name is required` error instead.
diff --git a/packages/core/src/v3/utils/ioSerialization.test.ts b/packages/core/src/v3/utils/ioSerialization.test.ts
new file mode 100644
index 00000000000..593ed256946
--- /dev/null
+++ b/packages/core/src/v3/utils/ioSerialization.test.ts
@@ -0,0 +1,29 @@
+import { describe, expect, it } from "vitest";
+import { stringifyIO } from "./ioSerialization.js";
+
+describe("stringifyIO", () => {
+  it("returns undefined data for undefined input", async () => {
+    const result = await stringifyIO(undefined);
+    expect(result).toEqual({ dataType: "application/json" });
+  });
+
+  it("returns plain text for string input", async () => {
+    const result = await stringifyIO("hello world");
+    expect(result).toEqual({ data: "hello world", dataType: "text/plain" });
+  });
+
+  it("serializes normal objects using super+json", async () => {
+    const result = await stringifyIO({ key: "value", num: 42 });
+    expect(result.dataType).toEqual("application/super+json");
+    expect(typeof result.data).toBe("string");
+  });
+
+  it("fallback returns string data when superjson fails", async () => {
+    // Create an object where superjson.stringify throws or handles non-standard values
+    const cyclic: any = { name: "test" };
+    cyclic.self = cyclic;
+
+    const result = await stringifyIO(cyclic);
+    expect(typeof result.data).toBe("string");
+  });
+});
diff --git a/packages/core/src/v3/utils/ioSerialization.ts b/packages/core/src/v3/utils/ioSerialization.ts
index a63a4397303..cd070c3be3c 100644
--- a/packages/core/src/v3/utils/ioSerialization.ts
+++ b/packages/core/src/v3/utils/ioSerialization.ts
@@ -96,7 +96,13 @@ export async function stringifyIO(value: any): Promise<IOPacket> {
 
     return { data, dataType: "application/super+json" };
   } catch {
-    return { data: value, dataType: "application/json" };
+    try {
+      const data = JSON.stringify(value, makeSafeReplacer());
+
+      return { data, dataType: "application/json" };
+    } catch {
+      return { data: String(value), dataType: "text/plain" };
+    }
   }
 }
 
diff --git a/packages/trigger-sdk/src/v3/envvars.test.ts b/packages/trigger-sdk/src/v3/envvars.test.ts
new file mode 100644
index 00000000000..e27a4cfe545
--- /dev/null
+++ b/packages/trigger-sdk/src/v3/envvars.test.ts
@@ -0,0 +1,192 @@
+import { taskContext } from "@trigger.dev/core/v3";
+import { createServer, type Server } from "node:http";
+import type { AddressInfo } from "node:net";
+import { afterEach, beforeEach, describe, expect, it } from "vitest";
+import { update } from "./envvars.js";
+
+describe("envvars.update outside a task context", () => {
+  let server: Server | undefined;
+  let requests: { method?: string; url?: string; body: string }[];
+  let previousApiUrl: string | undefined;
+  let previousSecretKey: string | undefined;
+  let previousAccessToken: string | undefined;
+
+  beforeEach(async () => {
+    requests = [];
+    previousApiUrl = process.env.TRIGGER_API_URL;
+    previousSecretKey = process.env.TRIGGER_SECRET_KEY;
+    previousAccessToken = process.env.TRIGGER_ACCESS_TOKEN;
+
+    delete process.env.TRIGGER_SECRET_KEY;
+
+    server = createServer((req, res) => {
+      let body = "";
+      req.on("data", (chunk) => {
+        body += chunk;
+      });
+      req.on("end", () => {
+        requests.push({ method: req.method, url: req.url, body });
+        res.writeHead(200, { "content-type": "application/json" });
+        res.end(JSON.stringify({ success: true }));
+      });
+    });
+
+    await new Promise<void>((resolve) => server!.listen(0, "127.0.0.1", resolve));
+
+    const { port } = server!.address() as AddressInfo;
+    process.env.TRIGGER_API_URL = `http://127.0.0.1:${port}`;
+    process.env.TRIGGER_ACCESS_TOKEN = "tr_test_token";
+  });
+
+  afterEach(async () => {
+    if (previousApiUrl === undefined) {
+      delete process.env.TRIGGER_API_URL;
+    } else {
+      process.env.TRIGGER_API_URL = previousApiUrl;
+    }
+
+    if (previousSecretKey === undefined) {
+      delete process.env.TRIGGER_SECRET_KEY;
+    } else {
+      process.env.TRIGGER_SECRET_KEY = previousSecretKey;
+    }
+
+    if (previousAccessToken === undefined) {
+      delete process.env.TRIGGER_ACCESS_TOKEN;
+    } else {
+      process.env.TRIGGER_ACCESS_TOKEN = previousAccessToken;
+    }
+
+    const running = server;
+    server = undefined;
+
+    if (running) {
+      await new Promise<void>((resolve, reject) =>
+        running.close((error) => (error ? reject(error) : resolve()))
+      );
+    }
+  });
+
+  it("sends a PUT for the named variable (regression #4264)", async () => {
+    expect(taskContext.ctx).toBeUndefined();
+
+    await expect(update("proj_xxx", "staging", "MY_VAR", { value: "hello" })).resolves.toEqual({
+      success: true,
+    });
+
+    expect(requests).toHaveLength(1);
+    expect(requests[0]?.method).toBe("PUT");
+    expect(requests[0]?.url).toBe("/api/v1/projects/proj_xxx/envvars/staging/MY_VAR");
+    expect(JSON.parse(requests[0]?.body ?? "")).toEqual({ value: "hello" });
+  });
+
+  it("throws a descriptive error when name is missing", () => {
+    expect(taskContext.ctx).toBeUndefined();
+
+    expect(() =>
+      update("proj_xxx", "staging", undefined as unknown as string, { value: "hello" })
+    ).toThrow("name is required");
+
+    expect(requests).toHaveLength(0);
+  });
+});
+
+describe("envvars.update inside a task context", () => {
+  let server: Server | undefined;
+  let requests: { method?: string; url?: string; body: string }[];
+  let previousApiUrl: string | undefined;
+  let previousSecretKey: string | undefined;
+  let previousAccessToken: string | undefined;
+
+  beforeEach(async () => {
+    requests = [];
+    previousApiUrl = process.env.TRIGGER_API_URL;
+    previousSecretKey = process.env.TRIGGER_SECRET_KEY;
+    previousAccessToken = process.env.TRIGGER_ACCESS_TOKEN;
+
+    delete process.env.TRIGGER_SECRET_KEY;
+
+    server = createServer((req, res) => {
+      let body = "";
+      req.on("data", (chunk) => {
+        body += chunk;
+      });
+      req.on("end", () => {
+        requests.push({ method: req.method, url: req.url, body });
+        res.writeHead(200, { "content-type": "application/json" });
+        res.end(JSON.stringify({ success: true }));
+      });
+    });
+
+    await new Promise<void>((resolve) => server!.listen(0, "127.0.0.1", resolve));
+
+    const { port } = server!.address() as AddressInfo;
+    process.env.TRIGGER_API_URL = `http://127.0.0.1:${port}`;
+    process.env.TRIGGER_ACCESS_TOKEN = "tr_test_token";
+
+    taskContext.setGlobalLocation({
+      ctx: {
+        project: { id: "proj_ctx_id", ref: "proj_ctx_ref", name: "Project Ctx" },
+        environment: { id: "env_ctx_id", slug: "dev", type: "DEVELOPMENT" },
+        organization: { id: "org_ctx_id", slug: "org_ctx", title: "Org Ctx" },
+        run: { id: "run_ctx_id", isTest: false },
+        task: { id: "task_ctx_id", filePath: "task.ts", exportName: "task" },
+
+      },
+    });
+  });
+
+  afterEach(async () => {
+    taskContext.clear();
+
+    if (previousApiUrl === undefined) {
+      delete process.env.TRIGGER_API_URL;
+    } else {
+      process.env.TRIGGER_API_URL = previousApiUrl;
+    }
+
+    if (previousSecretKey === undefined) {
+      delete process.env.TRIGGER_SECRET_KEY;
+    } else {
+      process.env.TRIGGER_SECRET_KEY = previousSecretKey;
+    }
+
+    if (previousAccessToken === undefined) {
+      delete process.env.TRIGGER_ACCESS_TOKEN;
+    } else {
+      process.env.TRIGGER_ACCESS_TOKEN = previousAccessToken;
+    }
+
+    const running = server;
+    server = undefined;
+
+    if (running) {
+      await new Promise<void>((resolve, reject) =>
+        running.close((error) => (error ? reject(error) : resolve()))
+      );
+    }
+  });
+
+  it("correctly parses explicit projectRef, slug, name parameters when taskContext exists", async () => {
+    await expect(update("proj_explicit", "staging", "MY_VAR", { value: "hello" })).resolves.toEqual({
+      success: true,
+    });
+
+    expect(requests).toHaveLength(1);
+    expect(requests[0]?.method).toBe("PUT");
+    expect(requests[0]?.url).toBe("/api/v1/projects/proj_explicit/envvars/staging/MY_VAR");
+    expect(JSON.parse(requests[0]?.body ?? "")).toEqual({ value: "hello" });
+  });
+
+  it("correctly uses taskContext defaults when only name and params are provided", async () => {
+    await expect(update("MY_VAR", { value: "hello_context" })).resolves.toEqual({
+      success: true,
+    });
+
+    expect(requests).toHaveLength(1);
+    expect(requests[0]?.method).toBe("PUT");
+    expect(requests[0]?.url).toBe("/api/v1/projects/proj_ctx_ref/envvars/dev/MY_VAR");
+    expect(JSON.parse(requests[0]?.body ?? "")).toEqual({ value: "hello_context" });
+  });
+});
+
diff --git a/packages/trigger-sdk/src/v3/envvars.ts b/packages/trigger-sdk/src/v3/envvars.ts
index 8ff68ab8907..201e70903a1 100644
--- a/packages/trigger-sdk/src/v3/envvars.ts
+++ b/packages/trigger-sdk/src/v3/envvars.ts
@@ -305,12 +305,12 @@ export function update(
 
   if (taskContext.ctx) {
     if (typeof slugOrParams === "string") {
-      $projectRef = slugOrParams;
-      $slug = slugOrParams ?? taskContext.ctx.environment.slug;
-      $name =
-        typeof nameOrRequestOptions === "string"
-          ? nameOrRequestOptions
-          : taskContext.ctx.environment.slug;
+      $projectRef = projectRefOrName;
+      $slug = slugOrParams;
+      if (typeof nameOrRequestOptions !== "string" || !nameOrRequestOptions) {
+        throw new Error("name is required");
+      }
+      $name = nameOrRequestOptions;
 
       if (!params) {
         throw new Error("params is required");
@@ -332,13 +332,17 @@ export function update(
       throw new Error("projectRef is required");
     }
 
+    if (typeof nameOrRequestOptions !== "string" || !nameOrRequestOptions) {
+      throw new Error("name is required");
+    }
+
     if (!params) {
       throw new Error("params is required");
     }
 
     $projectRef = projectRefOrName;
     $slug = slugOrParams;
-    $name = name!;
+    $name = nameOrRequestOptions;
     $params = params;
   }