diff --git a/packages/cli/cli/changes/unreleased/fix-register-api-definition-payload-too-large.yml b/packages/cli/cli/changes/unreleased/fix-register-api-definition-payload-too-large.yml
new file mode 100644
index 000000000000..72c73b9ba0d7
--- /dev/null
+++ b/packages/cli/cli/changes/unreleased/fix-register-api-definition-payload-too-large.yml
@@ -0,0 +1,6 @@
+- summary: |
+    Fix `PAYLOAD_TOO_LARGE` failures when publishing docs for large APIs with dynamic snippets. The
+    dynamic IRs were being sent inline in the `registerApiDefinition` request once per SDK language,
+    even though the registry only needs the language names to issue upload URLs (the IRs are uploaded
+    to S3 separately).
+  type: fix
diff --git a/packages/cli/generation/remote-generation/remote-workspace-runner/src/__test__/toRegisterDynamicIRsInput.test.ts b/packages/cli/generation/remote-generation/remote-workspace-runner/src/__test__/toRegisterDynamicIRsInput.test.ts
new file mode 100644
index 000000000000..9de5ad0d6ae2
--- /dev/null
+++ b/packages/cli/generation/remote-generation/remote-workspace-runner/src/__test__/toRegisterDynamicIRsInput.test.ts
@@ -0,0 +1,25 @@
+import { describe, expect, it } from "vitest";
+import { toRegisterDynamicIRsInput } from "../toRegisterDynamicIRsInput.js";
+
+describe("toRegisterDynamicIRsInput", () => {
+    it("returns undefined when there are no dynamic IRs", () => {
+        expect(toRegisterDynamicIRsInput(undefined)).toBeUndefined();
+    });
+
+    it("preserves the language keys", () => {
+        const result = toRegisterDynamicIRsInput({
+            python: { dynamicIR: { types: {} } },
+            typescript: { dynamicIR: { types: {} } }
+        });
+
+        expect(Object.keys(result ?? {}).sort()).toEqual(["python", "typescript"]);
+    });
+
+    it("strips the IR bodies so they are not sent in the registration request", () => {
+        const dynamicIR = { types: { User: { name: "User" } } };
+        const result = toRegisterDynamicIRsInput({ python: { dynamicIR }, go: { dynamicIR } });
+
+        expect(result).toEqual({ python: {}, go: {} });
+        expect(JSON.stringify(result)).not.toContain("User");
+    });
+});
diff --git a/packages/cli/generation/remote-generation/remote-workspace-runner/src/publishDocs.ts b/packages/cli/generation/remote-generation/remote-workspace-runner/src/publishDocs.ts
index 9be6aec06e2a..e350eaf52d8a 100644
--- a/packages/cli/generation/remote-generation/remote-workspace-runner/src/publishDocs.ts
+++ b/packages/cli/generation/remote-generation/remote-workspace-runner/src/publishDocs.ts
@@ -69,6 +69,7 @@ import { normalizeRepoUrlToHttps } from "./normalizeRepoUrl.js";
 import { publishDocsViaLedger } from "./publishDocsLedger.js";
 import { publishDocsViaLedgerPreview } from "./publishDocsLedgerPreview.js";
 import { retryWithBackoff } from "./retryWithBackoff.js";
+import { toRegisterDynamicIRsInput } from "./toRegisterDynamicIRsInput.js";
 import { asyncPool } from "./utils/asyncPool.js";
 
 const MEASURE_IMAGE_BATCH_SIZE = 10;
@@ -479,16 +480,22 @@ export async function publishDocs({
 
             const effectiveApiName = apiName ?? getOriginalName(ir.apiName);
 
+            const registerApiDefinitionRequest = {
+                orgId: CjsFdrSdk.OrgId(organization),
+                apiId: CjsFdrSdk.ApiId(effectiveApiName),
+                definition: apiDefinition,
+                dynamicIRs: toRegisterDynamicIRsInput(dynamicIRsByLanguage)
+            };
+            context.logger.debug(
+                `registerApiDefinition request body for ${effectiveApiName}: ${Buffer.byteLength(
+                    JSON.stringify(registerApiDefinitionRequest)
+                )} bytes, ${Object.keys(dynamicIRsByLanguage ?? {}).length} dynamic IR language(s) (IR bodies are uploaded separately)`
+            );
+
             let response;
             try {
                 response = await retryWithBackoff({
-                    fn: () =>
-                        fdr.api.register.registerApiDefinition({
-                            orgId: CjsFdrSdk.OrgId(organization),
-                            apiId: CjsFdrSdk.ApiId(effectiveApiName),
-                            definition: apiDefinition,
-                            dynamicIRs: dynamicIRsByLanguage
-                        }),
+                    fn: () => fdr.api.register.registerApiDefinition(registerApiDefinitionRequest),
                     maxRetries: REGISTER_MAX_RETRIES,
                     baseDelayMs: REGISTER_BASE_DELAY_MS,
                     jitterFactor: REGISTER_JITTER_FACTOR,
diff --git a/packages/cli/generation/remote-generation/remote-workspace-runner/src/toRegisterDynamicIRsInput.ts b/packages/cli/generation/remote-generation/remote-workspace-runner/src/toRegisterDynamicIRsInput.ts
new file mode 100644
index 000000000000..8e2028f42e94
--- /dev/null
+++ b/packages/cli/generation/remote-generation/remote-workspace-runner/src/toRegisterDynamicIRsInput.ts
@@ -0,0 +1,18 @@
+import type { APIV1Write } from "@fern-api/fdr-sdk";
+
+type DynamicIr = APIV1Write.DynamicIr;
+
+/**
+ * FDR only reads the language keys of `dynamicIRs` when registering an API definition — it mints one
+ * presigned upload URL per language, and the IRs themselves are uploaded directly to S3 afterwards.
+ * Sending the IR bodies inline duplicates the entire IR once per language in the registration request
+ * body, which can exceed the server's request size limit for large APIs.
+ */
+export function toRegisterDynamicIRsInput(
+    dynamicIRsByLanguage: Record<string, DynamicIr> | undefined
+): Record<string, DynamicIr> | undefined {
+    if (dynamicIRsByLanguage == null) {
+        return undefined;
+    }
+    return Object.fromEntries(Object.keys(dynamicIRsByLanguage).map((language) => [language, {}]));
+}