fix(anthropic): allow null content in compaction_delta streaming schema (#12471)

leog25 · Embedder · aayush-kapoor · web-flow · commit b094c0748613 · 2026-02-19T19:44:33.000-05:00
## Background PR #12384 introduced support for Anthropic's compaction feature, but the streaming Zod schema for compaction_delta events requires content to be a non-nullable string. Anthropic's API sends compaction_delta events with content: null (e.g. the initial frame before the compaction summary text), which causes Zod validation to fail at runtime. ## Summary Changed content: z.string() to content: z.string().nullish() in the compaction_delta streaming schema in packages/anthropic/src/anthropic-messages-api.ts. This matches the existing content_block_start schema for compaction, which already uses .nullish(). ## Manual Verification Reproduction requires streaming a conversation that exceeds the compaction trigger threshold (50k+ tokens) with @ai-sdk/anthropic, which triggers a compaction_delta event with content: null. This is not practical to verify without an API key and a large conversation, but the added regression test simulates this exact scenario by streaming a compaction_delta chunk with content: null. ## Checklist - Tests have been added / updated (for bug fixes / features) - Documentation has been added / updated (for bug fixes / features) - A patch changeset for relevant packages has been added (for bug fixes / features - run pnpm changeset in the project root) - I have reviewed this pull request (self-review) ## Related Issues Fixes #12470 --------- Co-authored-by: Embedder <215220128+embedder-dev@users.noreply.github.com> Co-authored-by: Aayush Kapoor <83492835+aayush-kapoor@users.noreply.github.com>
diff --git a/.changeset/great-grapes-dress.md b/.changeset/great-grapes-dress.md
@@ -0,0 +1,5 @@
+---
+'@ai-sdk/anthropic': patch
+---
+
+fix compaction_delta streaming schema to allow null content
diff --git a/packages/anthropic/src/anthropic-messages-api.ts b/packages/anthropic/src/anthropic-messages-api.ts
@@ -1128,7 +1128,7 @@ export const anthropicMessagesChunkSchema = lazySchema(() =>
           }),
           z.object({
             type: z.literal('compaction_delta'),
-            content: z.string(),
+            content: z.string().nullish(),
           }),
           z.object({
             type: z.literal('citations_delta'),
diff --git a/packages/anthropic/src/anthropic-messages-language-model.test.ts b/packages/anthropic/src/anthropic-messages-language-model.test.ts
@@ -5679,6 +5679,40 @@ describe('AnthropicMessagesLanguageModel', () => {
       });
     });
 
+    it('should handle compaction_delta with null content', async () => {
+      server.urls['https://api.anthropic.com/v1/messages'].response = {
+        type: 'stream-chunks',
+        chunks: [
+          `data: {"type":"message_start","message":{"id":"msg_test","type":"message","role":"assistant","model":"claude-3-haiku-20240307","stop_sequence":null,"usage":{"input_tokens":100,"output_tokens":0},"content":[],"stop_reason":null}}\n\n`,
+          `data: {"type":"content_block_start","index":0,"content_block":{"type":"compaction","content":null}}\n\n`,
+          `data: {"type":"content_block_delta","index":0,"delta":{"type":"compaction_delta","content":null}}\n\n`,
+          `data: {"type":"content_block_delta","index":0,"delta":{"type":"compaction_delta","content":"Summary of conversation."}}\n\n`,
+          `data: {"type":"content_block_stop","index":0}\n\n`,
+          `data: {"type":"message_delta","delta":{"stop_reason":"end_turn","stop_sequence":null},"usage":{"output_tokens":10}}\n\n`,
+          `data: {"type":"message_stop"}\n\n`,
+        ],
+      };
+
+      const { stream } = await model.doStream({
+        prompt: TEST_PROMPT,
+      });
+
+      const result = await convertReadableStreamToArray(stream);
+
+      // No parsing errors should occur (schema must accept null content)
+      const errors = result.filter(part => part.type === 'error');
+      expect(errors).toHaveLength(0);
+
+      const compactionDeltas = result.filter(
+        part => part.type === 'text-delta' && part.id === '0',
+      );
+      // null content delta should be skipped, only the string delta comes through
+      expect(compactionDeltas).toHaveLength(1);
+      expect((compactionDeltas[0] as { delta: string }).delta).toBe(
+        'Summary of conversation.',
+      );
+    });
+
     it('should stream tool deltas', async () => {
       server.urls['https://api.anthropic.com/v1/messages'].response = {
         type: 'stream-chunks',
diff --git a/packages/anthropic/src/anthropic-messages-language-model.ts b/packages/anthropic/src/anthropic-messages-language-model.ts
@@ -1840,11 +1840,13 @@ export class AnthropicMessagesLanguageModel implements LanguageModelV3 {
                 }
 
                 case 'compaction_delta': {
-                  controller.enqueue({
-                    type: 'text-delta',
-                    id: String(value.index),
-                    delta: value.delta.content,
-                  });
+                  if (value.delta.content != null) {
+                    controller.enqueue({
+                      type: 'text-delta',
+                      id: String(value.index),
+                      delta: value.delta.content,
+                    });
+                  }
 
                   return;
                 }

-Original file line number
+Diff line change
@@ @@ -0,0 +1,5 @@ @@
 +---
 +'@ai-sdk/anthropic': patch
 +---
++
 +fix compaction_delta streaming schema to allow null content