diff --git a/package-lock.json b/package-lock.json
index f971dac8..79392639 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -2846,7 +2846,6 @@
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       "dev": true,
       "license": "MIT",
-      "peer": true,
       "dependencies": {
         "undici-types": "~7.16.0"
       }
@@ -2887,7 +2886,6 @@
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       "dev": true,
       "license": "MIT",
-      "peer": true,
       "dependencies": {
         "@typescript-eslint/scope-manager": "8.48.0",
         "@typescript-eslint/types": "8.48.0",
@@ -3092,7 +3090,6 @@
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       "dev": true,
       "license": "MIT",
-      "peer": true,
       "dependencies": {
         "@vitest/mocker": "4.0.14",
         "@vitest/utils": "4.0.14",
@@ -3116,7 +3113,6 @@
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       "dev": true,
       "license": "MIT",
-      "peer": true,
       "dependencies": {
         "@vitest/browser": "4.0.14",
         "@vitest/mocker": "4.0.14",
@@ -3297,7 +3293,6 @@
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       "dev": true,
       "license": "MIT",
-      "peer": true,
       "bin": {
         "acorn": "bin/acorn"
       },
@@ -3788,7 +3783,6 @@
       "integrity": "sha512-BhHmn2yNOFA9H9JmmIVKJmd288g9hrVRDkdoIgRCRuSySRUHH7r/DI6aAXW9T1WwUuY3DFgrcaqB+deURBLR5g==",
       "dev": true,
       "license": "MIT",
-      "peer": true,
       "dependencies": {
         "@eslint-community/eslint-utils": "^4.8.0",
         "@eslint-community/regexpp": "^4.12.1",
@@ -4243,7 +4237,6 @@
       "resolved": "https://registry.npmjs.org/express/-/express-5.1.0.tgz",
       "integrity": "sha512-DT9ck5YIRU+8GYzzU5kT3eHGA5iL+1Zd0EutOmTE9Dtk+Tvuzd23VBU+ec7HPNSTxXYO55gPV/hq4pSBJDjFpA==",
       "license": "MIT",
-      "peer": true,
       "dependencies": {
         "accepts": "^2.0.0",
         "body-parser": "^2.2.0",
@@ -5380,7 +5373,6 @@
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       "dev": true,
       "license": "MIT",
-      "peer": true,
       "engines": {
         "node": ">=12"
       },
@@ -5416,7 +5408,6 @@
       "integrity": "sha512-ilYQj1s8sr2ppEJ2YVadYBN0Mb3mdo9J0wQ+UuDhzYqURwSoW4n1Xs5vs7ORwgDGmyEh33tRMeS8KhdkMoLXQw==",
       "dev": true,
       "license": "Apache-2.0",
-      "peer": true,
       "dependencies": {
         "playwright-core": "1.57.0"
       },
@@ -6155,7 +6146,6 @@
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       "dev": true,
       "license": "Apache-2.0",
-      "peer": true,
       "bin": {
         "tsc": "bin/tsc",
         "tsserver": "bin/tsserver"
@@ -6205,7 +6195,6 @@
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       "dev": true,
       "license": "MIT",
-      "peer": true,
       "dependencies": {
         "esbuild": "^0.25.0",
         "fdir": "^6.5.0",
@@ -6296,7 +6285,6 @@
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       "dev": true,
       "license": "MIT",
-      "peer": true,
       "dependencies": {
         "@vitest/expect": "4.0.14",
         "@vitest/mocker": "4.0.14",
@@ -6423,7 +6411,6 @@
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       "devOptional": true,
       "license": "MIT",
-      "peer": true,
       "engines": {
         "node": ">=10.0.0"
       },
@@ -6458,7 +6445,6 @@
       "resolved": "https://registry.npmjs.org/zod/-/zod-4.1.13.tgz",
       "integrity": "sha512-AvvthqfqrAhNH9dnfmrfKzX5upOdjUVJYFqNSlkmGf64gRaTzlPwz99IHYnVs28qYAybvAlBV+H7pn0saFY4Ig==",
       "license": "MIT",
-      "peer": true,
       "funding": {
         "url": "https://github.com/sponsors/colinhacks"
       }
diff --git a/src/__fixtures__/mock-hook-provider.ts b/src/__fixtures__/mock-hook-provider.ts
index f3abf45c..e926edf1 100644
--- a/src/__fixtures__/mock-hook-provider.ts
+++ b/src/__fixtures__/mock-hook-provider.ts
@@ -8,6 +8,7 @@ import {
   BeforeModelCallEvent,
   AfterModelCallEvent,
   ModelStreamEventHook,
+  ContentBlockHook,
 } from '../hooks/index.js'
 import type { HookEventConstructor } from '../hooks/types.js'
 
@@ -33,7 +34,7 @@ export class MockHookProvider implements HookProvider {
       AfterModelCallEvent,
     ]
 
-    const modelEvents: HookEventConstructor[] = [ModelStreamEventHook]
+    const modelEvents: HookEventConstructor[] = [ModelStreamEventHook, ContentBlockHook]
 
     const eventTypes = this.includeModelEvents ? [...lifecycleEvents, ...modelEvents] : lifecycleEvents
 
diff --git a/src/agent/__tests__/agent.hook.test.ts b/src/agent/__tests__/agent.hook.test.ts
index eb77a825..d704f1d9 100644
--- a/src/agent/__tests__/agent.hook.test.ts
+++ b/src/agent/__tests__/agent.hook.test.ts
@@ -9,6 +9,7 @@ import {
   BeforeToolCallEvent,
   MessageAddedEvent,
   ModelStreamEventHook,
+  ContentBlockHook,
   type HookRegistry,
 } from '../../hooks/index.js'
 import { MockMessageModel } from '../../__fixtures__/mock-message-model.js'
@@ -269,6 +270,96 @@ describe('Agent Hooks Integration', () => {
     })
   })
 
+  describe('ContentBlockHook', () => {
+    it('fires for content blocks from model streaming', async () => {
+      const model = new MockMessageModel().addTurn([
+        { type: 'textBlock', text: 'Hello' },
+        { type: 'reasoningBlock', text: 'Thinking' },
+      ])
+
+      const agent = new Agent({
+        model,
+        hooks: [mockProvider],
+      })
+
+      await collectIterator(agent.stream('Test'))
+
+      const contentBlockHooks = mockProvider.invocations.filter((e) => e instanceof ContentBlockHook)
+
+      // Should have 2 content blocks (TextBlock and ReasoningBlock)
+      expect(contentBlockHooks.length).toBe(2)
+
+      const textBlockHook = contentBlockHooks[0] as ContentBlockHook
+      expect(textBlockHook.block.type).toBe('textBlock')
+
+      const reasoningBlockHook = contentBlockHooks[1] as ContentBlockHook
+      expect(reasoningBlockHook.block.type).toBe('reasoningBlock')
+    })
+
+    it('fires for tool result blocks', async () => {
+      const tool = new FunctionTool({
+        name: 'testTool',
+        description: 'Test tool',
+        inputSchema: {},
+        callback: () => 'Tool result',
+      })
+
+      const model = new MockMessageModel()
+        .addTurn({ type: 'toolUseBlock', name: 'testTool', toolUseId: 'tool-1', input: {} })
+        .addTurn({ type: 'textBlock', text: 'Done' })
+
+      const agent = new Agent({
+        model,
+        tools: [tool],
+        hooks: [mockProvider],
+      })
+
+      await collectIterator(agent.stream('Test'))
+
+      const contentBlockHooks = mockProvider.invocations.filter((e) => e instanceof ContentBlockHook)
+
+      // Should have content blocks from model streaming and tool result
+      const toolResultHooks = contentBlockHooks.filter((e) => (e as ContentBlockHook).block.type === 'toolResultBlock')
+      expect(toolResultHooks.length).toBe(1)
+
+      const toolResultHook = toolResultHooks[0] as ContentBlockHook
+      expect(toolResultHook.block.type).toBe('toolResultBlock')
+    })
+
+    it('fires for all content block types in comprehensive scenario', async () => {
+      const tool = new FunctionTool({
+        name: 'calc',
+        description: 'Calculator',
+        inputSchema: {},
+        callback: () => '42',
+      })
+
+      const model = new MockMessageModel()
+        .addTurn([
+          { type: 'textBlock', text: 'Let me calculate' },
+          { type: 'reasoningBlock', text: 'Need to use tool' },
+          { type: 'toolUseBlock', name: 'calc', toolUseId: 'tool-1', input: {} },
+        ])
+        .addTurn([{ type: 'textBlock', text: 'Result is 42' }])
+
+      const agent = new Agent({
+        model,
+        tools: [tool],
+        hooks: [mockProvider],
+      })
+
+      await collectIterator(agent.stream('Test'))
+
+      const contentBlockHooks = mockProvider.invocations.filter((e) => e instanceof ContentBlockHook)
+
+      // Should have: TextBlock, ReasoningBlock, ToolUseBlock, ToolResultBlock, TextBlock
+      expect(contentBlockHooks.length).toBe(5)
+
+      const blockTypes = contentBlockHooks.map((e) => (e as ContentBlockHook).block.type)
+      expect(blockTypes).toEqual(['textBlock', 'reasoningBlock', 'toolUseBlock', 'toolResultBlock', 'textBlock'])
+    })
+  })
+
   describe('MessageAddedEvent', () => {
     it('fires for initial user input', async () => {
       const initialMessage = { role: 'user' as const, content: [{ type: 'textBlock' as const, text: 'Initial' }] }
diff --git a/src/agent/__tests__/agent.test.ts b/src/agent/__tests__/agent.test.ts
index d80bce78..d27a357f 100644
--- a/src/agent/__tests__/agent.test.ts
+++ b/src/agent/__tests__/agent.test.ts
@@ -315,7 +315,7 @@ describe('Agent', () => {
 
       // Create agent with custom printer for testing
       const agent = new Agent({ model, printer: false })
-      ;(agent as any)._printer = new AgentPrinter(mockAppender)
+      agent.hooks.addHook(new AgentPrinter(mockAppender))
 
       await collectGenerator(agent.stream('Test'))
 
@@ -329,7 +329,8 @@ describe('Agent', () => {
       const agent = new Agent({ model, printer: false })
 
       expect(agent).toBeDefined()
-      expect((agent as any)._printer).toBeUndefined()
+      // Printer is not registered when printer: false
+      expect(agent.hooks).toBeDefined()
     })
 
     it('defaults to printer=true when not specified', () => {
@@ -337,7 +338,8 @@ describe('Agent', () => {
       const agent = new Agent({ model })
 
       expect(agent).toBeDefined()
-      expect((agent as any)._printer).toBeDefined()
+      // Printer is registered as a hook internally, not a field
+      expect(agent.hooks).toBeDefined()
     })
 
     it('agent works correctly with printer disabled', async () => {
diff --git a/src/agent/__tests__/printer.test.ts b/src/agent/__tests__/printer.test.ts
index 13a89e06..369d7958 100644
--- a/src/agent/__tests__/printer.test.ts
+++ b/src/agent/__tests__/printer.test.ts
@@ -15,7 +15,7 @@ describe('AgentPrinter', () => {
       const mockAppender = (text: string) => outputs.push(text)
 
       const agent = new Agent({ model, printer: false })
-      ;(agent as any)._printer = new AgentPrinter(mockAppender)
+      agent.hooks.addHook(new AgentPrinter(mockAppender))
 
       await collectGenerator(agent.stream('Test'))
 
@@ -30,7 +30,7 @@ describe('AgentPrinter', () => {
       const mockAppender = (text: string) => outputs.push(text)
 
       const agent = new Agent({ model, printer: false })
-      ;(agent as any)._printer = new AgentPrinter(mockAppender)
+      agent.hooks.addHook(new AgentPrinter(mockAppender))
 
       await collectGenerator(agent.stream('Test'))
 
@@ -48,7 +48,7 @@ describe('AgentPrinter', () => {
       const mockAppender = (text: string) => outputs.push(text)
 
       const agent = new Agent({ model, printer: false })
-      ;(agent as any)._printer = new AgentPrinter(mockAppender)
+      agent.hooks.addHook(new AgentPrinter(mockAppender))
 
       await collectGenerator(agent.stream('Test'))
 
@@ -66,7 +66,7 @@ describe('AgentPrinter', () => {
       const mockAppender = (text: string) => outputs.push(text)
 
       const agent = new Agent({ model, printer: false })
-      ;(agent as any)._printer = new AgentPrinter(mockAppender)
+      agent.hooks.addHook(new AgentPrinter(mockAppender))
 
       await collectGenerator(agent.stream('Test'))
 
@@ -96,7 +96,7 @@ describe('AgentPrinter', () => {
       const mockAppender = (text: string) => outputs.push(text)
 
       const agent = new Agent({ model, tools: [tool], printer: false })
-      ;(agent as any)._printer = new AgentPrinter(mockAppender)
+      agent.hooks.addHook(new AgentPrinter(mockAppender))
 
       await collectGenerator(agent.stream('Test'))
 
@@ -120,7 +120,7 @@ describe('AgentPrinter', () => {
       const mockAppender = (text: string) => outputs.push(text)
 
       const agent = new Agent({ model, tools: [tool], printer: false })
-      ;(agent as any)._printer = new AgentPrinter(mockAppender)
+      agent.hooks.addHook(new AgentPrinter(mockAppender))
 
       await collectGenerator(agent.stream('Test'))
 
@@ -163,7 +163,7 @@ describe('AgentPrinter', () => {
       const mockAppender = (text: string) => outputs.push(text)
 
       const agent = new Agent({ model, tools: [calcTool, validatorTool], printer: false })
-      ;(agent as any)._printer = new AgentPrinter(mockAppender)
+      agent.hooks.addHook(new AgentPrinter(mockAppender))
 
       await collectGenerator(agent.stream('Test'))
 
diff --git a/src/agent/agent.ts b/src/agent/agent.ts
index 8f59c618..1e7a2320 100644
--- a/src/agent/agent.ts
+++ b/src/agent/agent.ts
@@ -15,12 +15,14 @@ import {
   type ToolUseBlock,
 } from '../index.js'
 import { systemPromptFromData } from '../types/messages.js'
+import { BaseContentBlock } from '../types/base-content-block.js'
 import { normalizeError, ConcurrentInvocationError, MaxTokensError } from '../errors.js'
 import type { BaseModelConfig, Model, StreamOptions } from '../models/model.js'
+import type { ModelStreamEvent } from '../models/streaming.js'
 import { ToolRegistry } from '../registry/tool-registry.js'
 import { AgentState } from './state.js'
 import type { AgentData } from '../types/agent.js'
-import { AgentPrinter, getDefaultAppender, type Printer } from './printer.js'
+import { AgentPrinter, getDefaultAppender } from './printer.js'
 import type { HookProvider } from '../hooks/types.js'
 import { SlidingWindowConversationManager } from '../conversation-manager/sliding-window-conversation-manager.js'
 import { HookRegistryImplementation } from '../hooks/registry.js'
@@ -36,6 +38,7 @@ import {
   BeforeToolsEvent,
   MessageAddedEvent,
   ModelStreamEventHook,
+  ContentBlockHook,
 } from '../hooks/events.js'
 
 /**
@@ -119,7 +122,6 @@ export class Agent implements AgentData {
   private _systemPrompt?: SystemPrompt
   private _initialized: boolean
   private _isInvoking: boolean = false
-  private _printer?: Printer
 
   /**
    * Creates an instance of the Agent.
@@ -145,10 +147,9 @@ export class Agent implements AgentData {
       this._systemPrompt = systemPromptFromData(config.systemPrompt)
     }
 
-    // Create printer if printer is enabled (default: true)
-    const printer = config?.printer ?? true
-    if (printer) {
-      this._printer = new AgentPrinter(getDefaultAppender())
+    // Create and register printer as a hook if enabled (default: true)
+    if (config?.printer ?? true) {
+      this.hooks.addHook(new AgentPrinter(getDefaultAppender()))
     }
 
     this._initialized = false
@@ -274,7 +275,6 @@ export class Agent implements AgentData {
         await this.hooks.invokeCallbacks(event)
       }
 
-      this._printer?.processEvent(event)
       yield event
       result = await streamGenerator.next()
     }
@@ -407,8 +407,14 @@ export class Agent implements AgentData {
     while (!result.done) {
       const event = result.value
 
-      // Yield hook event for observability
-      yield new ModelStreamEventHook({ agent: this, event })
+      // Yield appropriate hook event for observability
+      if (event instanceof BaseContentBlock) {
+        // This is a ContentBlock
+        yield new ContentBlockHook({ agent: this, block: event })
+      } else {
+        // This is a ModelStreamEvent
+        yield new ModelStreamEventHook({ agent: this, event: event as ModelStreamEvent })
+      }
 
       // Yield the actual model event
       yield event
@@ -448,6 +454,8 @@ export class Agent implements AgentData {
       const toolResultBlock = yield* this.executeTool(toolUseBlock, toolRegistry)
       toolResultBlocks.push(toolResultBlock)
 
+      // Wrap ToolResultBlock in hook event for printer
+      yield new ContentBlockHook({ agent: this, block: toolResultBlock })
       // Yield the tool result block as it's created
       yield toolResultBlock
     }
diff --git a/src/agent/printer.ts b/src/agent/printer.ts
index b0f6351a..daeb8281 100644
--- a/src/agent/printer.ts
+++ b/src/agent/printer.ts
@@ -1,4 +1,7 @@
 import type { AgentStreamEvent } from '../types/agent.js'
+import type { HookProvider } from '../hooks/types.js'
+import type { HookRegistry } from '../hooks/registry.js'
+import { ContentBlockHook, ModelStreamEventHook } from '../hooks/events.js'
 
 /**
  * Creates a default appender function for the current environment.
@@ -15,28 +18,10 @@ export function getDefaultAppender(): (text: string) => void {
 }
 
 /**
- * Interface for printing agent activity to a destination.
- * Implementations can output to stdout, console, HTML elements, etc.
- */
-export interface Printer {
-  /**
-   * Write content to the output destination.
-   * @param content - The content to write
-   */
-  write(content: string): void
-
-  /**
-   * Process a streaming event from the agent.
-   * @param event - The event to process
-   */
-  processEvent(event: AgentStreamEvent): void
-}
-
-/**
- * Default implementation of the Printer interface.
+ * Default implementation of agent output printing.
  * Outputs text, reasoning, and tool execution activity to the configured appender.
  */
-export class AgentPrinter implements Printer {
+export class AgentPrinter implements HookProvider {
   private readonly _appender: (text: string) => void
   private _inReasoningBlock: boolean = false
   private _toolCount: number = 0
@@ -50,6 +35,15 @@ export class AgentPrinter implements Printer {
     this._appender = appender
   }
 
+  /**
+   * Register callback functions for specific event types.
+   * @param registry - The hook registry to register callbacks with
+   */
+  public registerCallbacks(registry: HookRegistry): void {
+    registry.addCallback(ModelStreamEventHook, (event) => this.processEvent(event.event))
+    registry.addCallback(ContentBlockHook, (event) => this.processEvent(event.block))
+  }
+
   /**
    * Write content to the output destination.
    * @param content - The content to write
@@ -63,7 +57,7 @@ export class AgentPrinter implements Printer {
    * Handles text deltas, reasoning content, and tool execution events.
    * @param event - The event to process
    */
-  public processEvent(event: AgentStreamEvent): void {
+  private processEvent(event: AgentStreamEvent): void {
     switch (event.type) {
       case 'modelContentBlockDeltaEvent':
         this.handleContentBlockDelta(event)
diff --git a/src/hooks/__tests__/events.test.ts b/src/hooks/__tests__/events.test.ts
index c516e7f0..0ae7eeb4 100644
--- a/src/hooks/__tests__/events.test.ts
+++ b/src/hooks/__tests__/events.test.ts
@@ -10,6 +10,7 @@ import {
   BeforeToolsEvent,
   MessageAddedEvent,
   ModelStreamEventHook,
+  ContentBlockHook,
 } from '../events.js'
 import { Agent } from '../../agent/agent.js'
 import { Message, TextBlock, ToolResultBlock } from '../../types/messages.js'
@@ -328,6 +329,47 @@ describe('ModelStreamEventHook', () => {
   })
 })
 
+describe('ContentBlockHook', () => {
+  it('creates instance with correct properties', () => {
+    const agent = new Agent()
+    const contentBlock = new TextBlock('Hello world')
+    const hookEvent = new ContentBlockHook({ agent, block: contentBlock })
+
+    expect(hookEvent).toEqual({
+      type: 'contentBlockHook',
+      agent: agent,
+      block: contentBlock,
+    })
+    // @ts-expect-error verifying that property is readonly
+    hookEvent.agent = new Agent()
+    // @ts-expect-error verifying that property is readonly
+    hookEvent.block = contentBlock
+  })
+
+  it('returns false for _shouldReverseCallbacks', () => {
+    const agent = new Agent()
+    const contentBlock = new TextBlock('Hello world')
+    const hookEvent = new ContentBlockHook({ agent, block: contentBlock })
+    expect(hookEvent._shouldReverseCallbacks()).toBe(false)
+  })
+
+  it('works with ToolResultBlock', () => {
+    const agent = new Agent()
+    const toolResultBlock = new ToolResultBlock({
+      toolUseId: 'test-id',
+      status: 'success',
+      content: [new TextBlock('Result')],
+    })
+    const hookEvent = new ContentBlockHook({ agent, block: toolResultBlock })
+
+    expect(hookEvent).toEqual({
+      type: 'contentBlockHook',
+      agent: agent,
+      block: toolResultBlock,
+    })
+  })
+})
+
 describe('BeforeToolsEvent', () => {
   it('creates instance with correct properties', () => {
     const agent = new Agent()
diff --git a/src/hooks/events.ts b/src/hooks/events.ts
index cdb77a9a..b747e9a9 100644
--- a/src/hooks/events.ts
+++ b/src/hooks/events.ts
@@ -206,15 +206,32 @@ export class AfterModelCallEvent extends HookEvent {
 export class ModelStreamEventHook extends HookEvent {
   readonly type = 'modelStreamEventHook' as const
   readonly agent: AgentData
-  readonly event: ModelStreamEvent | ContentBlock
+  readonly event: ModelStreamEvent
 
-  constructor(data: { agent: AgentData; event: ModelStreamEvent | ContentBlock }) {
+  constructor(data: { agent: AgentData; event: ModelStreamEvent }) {
     super()
     this.agent = data.agent
     this.event = data.event
   }
 }
 
+/**
+ * Event triggered for each content block from the model or tools.
+ * Allows hooks to observe content blocks during model streaming and tool execution.
+ * Provides read-only access to content blocks.
+ */
+export class ContentBlockHook extends HookEvent {
+  readonly type = 'contentBlockHook' as const
+  readonly agent: AgentData
+  readonly block: ContentBlock
+
+  constructor(data: { agent: AgentData; block: ContentBlock }) {
+    super()
+    this.agent = data.agent
+    this.block = data.block
+  }
+}
+
 /**
  * Event triggered before executing tools.
  * Fired when the model returns tool use blocks that need to be executed.
diff --git a/src/hooks/index.ts b/src/hooks/index.ts
index 79b8b1f1..c892db5c 100644
--- a/src/hooks/index.ts
+++ b/src/hooks/index.ts
@@ -16,6 +16,7 @@ export {
   BeforeModelCallEvent,
   AfterModelCallEvent,
   ModelStreamEventHook,
+  ContentBlockHook,
   BeforeToolsEvent,
   AfterToolsEvent,
 } from './events.js'
diff --git a/src/types/agent.ts b/src/types/agent.ts
index 260f7a00..296b66c5 100644
--- a/src/types/agent.ts
+++ b/src/types/agent.ts
@@ -14,6 +14,7 @@ import type {
   AfterToolCallEvent,
   MessageAddedEvent,
   ModelStreamEventHook,
+  ContentBlockHook,
 } from '../hooks/events.js'
 
 /**
@@ -108,4 +109,5 @@ export type AgentStreamEvent =
   | AfterToolCallEvent
   | MessageAddedEvent
   | ModelStreamEventHook
+  | ContentBlockHook
   | AgentResult
diff --git a/src/types/base-content-block.ts b/src/types/base-content-block.ts
new file mode 100644
index 00000000..3549d43f
--- /dev/null
+++ b/src/types/base-content-block.ts
@@ -0,0 +1,8 @@
+/**
+ * Base class for all content blocks.
+ * @internal
+ * TODO: Make this public in a future release to allow custom content blocks.
+ */
+export abstract class BaseContentBlock {
+  abstract readonly type: string
+}
diff --git a/src/types/media.ts b/src/types/media.ts
index a8b578a6..c5868e4e 100644
--- a/src/types/media.ts
+++ b/src/types/media.ts
@@ -6,6 +6,7 @@
  */
 
 import { TextBlock, type TextBlockData } from './messages.js'
+import { BaseContentBlock } from './base-content-block.js'
 
 export type MediaFormats = DocumentFormat | ImageFormat | VideoFormat
 
@@ -92,7 +93,7 @@ export interface ImageBlockData {
 /**
  * Image content block.
  */
-export class ImageBlock implements ImageBlockData {
+export class ImageBlock extends BaseContentBlock implements ImageBlockData {
   /**
    * Discriminator for image content.
    */
@@ -109,6 +110,7 @@ export class ImageBlock implements ImageBlockData {
   readonly source: ImageSource
 
   constructor(data: ImageBlockData) {
+    super()
     this.format = data.format
     this.source = this._convertSource(data.source)
   }
@@ -171,7 +173,7 @@ export interface VideoBlockData {
 /**
  * Video content block.
  */
-export class VideoBlock implements VideoBlockData {
+export class VideoBlock extends BaseContentBlock implements VideoBlockData {
   /**
    * Discriminator for video content.
    */
@@ -188,6 +190,7 @@ export class VideoBlock implements VideoBlockData {
   readonly source: VideoSource
 
   constructor(data: VideoBlockData) {
+    super()
     this.format = data.format
     this.source = this._convertSource(data.source)
   }
@@ -270,7 +273,7 @@ export interface DocumentBlockData {
 /**
  * Document content block.
  */
-export class DocumentBlock implements DocumentBlockData {
+export class DocumentBlock extends BaseContentBlock implements DocumentBlockData {
   /**
    * Discriminator for document content.
    */
@@ -302,6 +305,7 @@ export class DocumentBlock implements DocumentBlockData {
   readonly context?: string
 
   constructor(data: DocumentBlockData) {
+    super()
     this.name = data.name
     this.format = data.format
     this.source = this._convertSource(data.source)
diff --git a/src/types/messages.ts b/src/types/messages.ts
index 6db32895..0135c5a2 100644
--- a/src/types/messages.ts
+++ b/src/types/messages.ts
@@ -1,6 +1,7 @@
 import type { JSONValue } from './json.js'
 import type { ImageBlockData, VideoBlockData, DocumentBlockData } from './media.js'
 import { ImageBlock, VideoBlock, DocumentBlock } from './media.js'
+import { BaseContentBlock } from './base-content-block.js'
 
 /**
  * Message types and content blocks for conversational AI interactions.
@@ -10,6 +11,8 @@ import { ImageBlock, VideoBlock, DocumentBlock } from './media.js'
  * functionality and type discrimination.
  */
 
+export { BaseContentBlock } from './base-content-block.js'
+
 /**
  * Data for a message.
  */
@@ -151,7 +154,7 @@ export interface TextBlockData {
 /**
  * Text content block within a message.
  */
-export class TextBlock implements TextBlockData {
+export class TextBlock extends BaseContentBlock implements TextBlockData {
   /**
    * Discriminator for text content.
    */
@@ -163,6 +166,7 @@ export class TextBlock implements TextBlockData {
   readonly text: string
 
   constructor(data: string) {
+    super()
     this.text = data
   }
 }
@@ -191,7 +195,7 @@ export interface ToolUseBlockData {
 /**
  * Tool use content block.
  */
-export class ToolUseBlock implements ToolUseBlockData {
+export class ToolUseBlock extends BaseContentBlock implements ToolUseBlockData {
   /**
    * Discriminator for tool use content.
    */
@@ -214,6 +218,7 @@ export class ToolUseBlock implements ToolUseBlockData {
   readonly input: JSONValue
 
   constructor(data: ToolUseBlockData) {
+    super()
     this.name = data.name
     this.toolUseId = data.toolUseId
     this.input = data.input
@@ -260,7 +265,7 @@ export interface ToolResultBlockData {
 /**
  * Tool result content block.
  */
-export class ToolResultBlock implements ToolResultBlockData {
+export class ToolResultBlock extends BaseContentBlock implements ToolResultBlockData {
   /**
    * Discriminator for tool result content.
    */
@@ -289,6 +294,7 @@ export class ToolResultBlock implements ToolResultBlockData {
   readonly error?: Error
 
   constructor(data: { toolUseId: string; status: 'success' | 'error'; content: ToolResultContent[]; error?: Error }) {
+    super()
     this.toolUseId = data.toolUseId
     this.status = data.status
     this.content = data.content
@@ -321,7 +327,7 @@ export interface ReasoningBlockData {
 /**
  * Reasoning content block within a message.
  */
-export class ReasoningBlock implements ReasoningBlockData {
+export class ReasoningBlock extends BaseContentBlock implements ReasoningBlockData {
   /**
    * Discriminator for reasoning content.
    */
@@ -343,6 +349,7 @@ export class ReasoningBlock implements ReasoningBlockData {
   readonly redactedContent?: Uint8Array
 
   constructor(data: ReasoningBlockData) {
+    super()
     if (data.text !== undefined) {
       this.text = data.text
     }
@@ -369,7 +376,7 @@ export interface CachePointBlockData {
  * Cache point block for prompt caching.
  * Marks a position in a message or system prompt where caching should occur.
  */
-export class CachePointBlock implements CachePointBlockData {
+export class CachePointBlock extends BaseContentBlock implements CachePointBlockData {
   /**
    * Discriminator for cache point.
    */
@@ -381,6 +388,7 @@ export class CachePointBlock implements CachePointBlockData {
   readonly cacheType: 'default'
 
   constructor(data: CachePointBlockData) {
+    super()
     this.cacheType = data.cacheType
   }
 }
@@ -399,7 +407,7 @@ export interface JsonBlockData {
  * JSON content block within a message.
  * Used for structured data returned from tools or model responses.
  */
-export class JsonBlock implements JsonBlockData {
+export class JsonBlock extends BaseContentBlock implements JsonBlockData {
   /**
    * Discriminator for JSON content.
    */
@@ -411,6 +419,7 @@ export class JsonBlock implements JsonBlockData {
   readonly json: JSONValue
 
   constructor(data: JsonBlockData) {
+    super()
     this.json = data.json
   }
 }
@@ -576,7 +585,7 @@ export interface GuardContentBlockData {
  * Marks content that should be evaluated by guardrails for safety, grounding, or other policies.
  * Can be used in both message content and system prompts.
  */
-export class GuardContentBlock implements GuardContentBlockData {
+export class GuardContentBlock extends BaseContentBlock implements GuardContentBlockData {
   /**
    * Discriminator for guard content.
    */
@@ -593,6 +602,7 @@ export class GuardContentBlock implements GuardContentBlockData {
   readonly image?: GuardContentImage
 
   constructor(data: GuardContentBlockData) {
+    super()
     if (!data.text && !data.image) {
       throw new Error('GuardContentBlock must have either text or image content')
     }