diff --git a/src/application/services/MemoryService.ts b/src/application/services/MemoryService.ts
index ac904257..c8f899dc 100644
--- a/src/application/services/MemoryService.ts
+++ b/src/application/services/MemoryService.ts
@@ -38,7 +38,7 @@ export class MemoryService implements IMemoryService {
         this.logger?.warn('Skipping trailer write for non-HEAD commit', { sha: targetSha });
       } else {
         try {
-          const trailers = this.buildTrailers(memory);
+          const trailers = this.buildTrailers(memory, options);
           this.trailerService.addTrailers(trailers, options?.cwd);
           this.logger?.info('Trailers written', { count: trailers.length, sha: memory.sha });
         } catch (err) {
@@ -62,7 +62,7 @@ export class MemoryService implements IMemoryService {
     return value.replace(/\r?\n+/g, ' ').trim();
   }
 
-  private buildTrailers(memory: IMemoryEntity): ITrailer[] {
+  private buildTrailers(memory: IMemoryEntity, options?: ICreateMemoryOptions): ITrailer[] {
     const trailers: ITrailer[] = [
       { key: MEMORY_TYPE_TO_TRAILER_KEY[memory.type], value: this.normalizeTrailerValue(memory.content) },
       { key: AI_TRAILER_KEYS.CONFIDENCE, value: memory.confidence },
@@ -73,6 +73,14 @@ export class MemoryService implements IMemoryService {
       trailers.push({ key: AI_TRAILER_KEYS.TAGS, value: this.normalizeTrailerValue(memory.tags.join(', ')) });
     }
 
+    if (options?.agent) {
+      trailers.push({ key: AI_TRAILER_KEYS.AGENT, value: this.normalizeTrailerValue(options.agent) });
+    }
+
+    if (options?.model) {
+      trailers.push({ key: AI_TRAILER_KEYS.MODEL, value: this.normalizeTrailerValue(options.model) });
+    }
+
     return trailers;
   }
 
diff --git a/src/cli.ts b/src/cli.ts
index a84a091d..a8ead64a 100644
--- a/src/cli.ts
+++ b/src/cli.ts
@@ -39,6 +39,8 @@ program
   .option('--confidence <level>', 'Confidence: verified, high, medium, low', 'high')
   .option('--lifecycle <tier>', 'Lifecycle: permanent, project, session', 'project')
   .option('--tags <tags>', 'Comma-separated tags')
+  .option('--agent <name>', 'AI agent name (default: auto-detect from $GIT_MEM_AGENT / $CLAUDE_CODE)')
+  .option('--model <name>', 'AI model identifier (default: $GIT_MEM_MODEL)')
   .option('--no-trailers', 'Skip writing AI-* trailers to the commit message')
   .action((text, options) => rememberCommand(text, options, logger));
 
diff --git a/src/commands/remember.ts b/src/commands/remember.ts
index 87b2a0bf..0f82aa8f 100644
--- a/src/commands/remember.ts
+++ b/src/commands/remember.ts
@@ -15,6 +15,8 @@ interface IRememberOptions {
   lifecycle?: string;
   tags?: string;
   noTrailers?: boolean;
+  agent?: string;
+  model?: string;
 }
 
 export async function rememberCommand(text: string, options: IRememberOptions, logger?: ILogger): Promise<void> {
@@ -22,6 +24,14 @@ export async function rememberCommand(text: string, options: IRememberOptions, l
   const { memoryService, logger: log } = container.cradle;
   log.info('Command invoked', { type: options.type || 'fact' });
 
+  // Resolve agent: explicit flag > $GIT_MEM_AGENT > $CLAUDE_CODE heuristic
+  const agent = options.agent
+    || process.env.GIT_MEM_AGENT
+    || (process.env.CLAUDE_CODE ? 'Claude-Code' : undefined);
+
+  // Resolve model: explicit flag > $GIT_MEM_MODEL
+  const model = options.model || process.env.GIT_MEM_MODEL || undefined;
+
   const memory = memoryService.remember(text, {
     sha: options.commit,
     type: (options.type || 'fact') as MemoryType,
@@ -29,6 +39,8 @@ export async function rememberCommand(text: string, options: IRememberOptions, l
     lifecycle: (options.lifecycle || 'project') as MemoryLifecycle,
     tags: options.tags,
     trailers: !options.noTrailers,
+    agent,
+    model,
   });
 
   console.log(`Remembered: ${memory.content}`);
diff --git a/src/domain/entities/IMemoryEntity.ts b/src/domain/entities/IMemoryEntity.ts
index 7cd3ce0f..9db94911 100644
--- a/src/domain/entities/IMemoryEntity.ts
+++ b/src/domain/entities/IMemoryEntity.ts
@@ -71,6 +71,10 @@ export interface ICreateMemoryOptions {
   readonly cwd?: string;
   /** Write AI-* trailers to the commit message (default: true). */
   readonly trailers?: boolean;
+  /** AI agent name (e.g. 'Claude-Code'). */
+  readonly agent?: string;
+  /** AI model identifier (e.g. 'claude-opus-4-6'). */
+  readonly model?: string;
 }
 
 /**
diff --git a/src/domain/entities/ITrailer.ts b/src/domain/entities/ITrailer.ts
index e11d74f1..63cf22b8 100644
--- a/src/domain/entities/ITrailer.ts
+++ b/src/domain/entities/ITrailer.ts
@@ -33,6 +33,7 @@ export const AI_TRAILER_KEYS = {
   LIFECYCLE: 'AI-Lifecycle',
   MEMORY_ID: 'AI-Memory-Id',
   AGENT: 'AI-Agent',
+  MODEL: 'AI-Model',
 } as const;
 
 /**
diff --git a/src/hooks/prepare-commit-msg.ts b/src/hooks/prepare-commit-msg.ts
index 77176f0b..dcf91eca 100644
--- a/src/hooks/prepare-commit-msg.ts
+++ b/src/hooks/prepare-commit-msg.ts
@@ -1,12 +1,13 @@
 /**
  * prepare-commit-msg git hook
  *
- * Installs/uninstalls a git hook that injects AI-Agent trailers
- * into commit messages when an AI-assisted session is detected.
+ * Installs/uninstalls a git hook that injects AI-Agent and AI-Model
+ * trailers into commit messages when an AI-assisted session is detected.
  *
  * Detection heuristics (checked in order):
  *   - $GIT_MEM_AGENT env var (explicit, user-defined agent string)
  *   - $CLAUDE_CODE env var (Claude Code session)
+ *   - $GIT_MEM_MODEL env var (explicit, user-defined model string)
  *
  * The hook uses `git interpret-trailers` for proper formatting.
  */
@@ -15,8 +16,11 @@ import { existsSync, readFileSync, writeFileSync, renameSync, unlinkSync, chmodS
 import { join, resolve } from 'path';
 import { execFileSync } from 'child_process';
 
-/** Fingerprint comment used to detect our hook. */
-const HOOK_FINGERPRINT = '# git-mem:prepare-commit-msg v1';
+/** Prefix used to detect any version of our hook. */
+const HOOK_FINGERPRINT_PREFIX = '# git-mem:prepare-commit-msg';
+
+/** Full fingerprint with version — used for upgrade detection. */
+const HOOK_FINGERPRINT = `${HOOK_FINGERPRINT_PREFIX} v2`;
 
 /**
  * The shell hook script.
@@ -24,7 +28,7 @@ const HOOK_FINGERPRINT = '# git-mem:prepare-commit-msg v1';
  */
 const HOOK_SCRIPT = `#!/bin/sh
 ${HOOK_FINGERPRINT}
-# Injects AI-Agent trailer when an AI-assisted session is detected.
+# Injects AI-Agent and AI-Model trailers when an AI-assisted session is detected.
 
 COMMIT_MSG_FILE="$1"
 COMMIT_SOURCE="$2"
@@ -42,14 +46,26 @@ elif [ -n "$CLAUDE_CODE" ]; then
   AGENT="Claude-Code"
 fi
 
+# Detect AI model
+MODEL=""
+if [ -n "$GIT_MEM_MODEL" ]; then
+  MODEL="$GIT_MEM_MODEL"
+fi
+
 # No agent detected — exit silently
 [ -z "$AGENT" ] && exit 0
 
 # Skip if AI-Agent trailer already present
 grep -q "^AI-Agent:" "$COMMIT_MSG_FILE" && exit 0
 
-# Append trailer using git's built-in formatter
+# Append agent trailer using git's built-in formatter
 git interpret-trailers --in-place --trailer "AI-Agent: $AGENT" "$COMMIT_MSG_FILE"
+
+# Append model trailer if detected
+if [ -n "$MODEL" ]; then
+  grep -q "^AI-Model:" "$COMMIT_MSG_FILE" ||
+    git interpret-trailers --in-place --trailer "AI-Model: $MODEL" "$COMMIT_MSG_FILE"
+fi
 `;
 
 /**
@@ -70,9 +86,18 @@ function findGitDir(cwd: string): string {
 }
 
 /**
- * Check if an existing hook file was installed by git-mem.
+ * Check if an existing hook file was installed by git-mem (any version).
  */
 function isGitMemHook(hookPath: string): boolean {
+  if (!existsSync(hookPath)) return false;
+  const content = readFileSync(hookPath, 'utf8');
+  return content.includes(HOOK_FINGERPRINT_PREFIX);
+}
+
+/**
+ * Check if an installed hook is the current version.
+ */
+function isCurrentVersion(hookPath: string): boolean {
   if (!existsSync(hookPath)) return false;
   const content = readFileSync(hookPath, 'utf8');
   return content.includes(HOOK_FINGERPRINT);
@@ -91,6 +116,7 @@ export interface IHookInstallResult {
  * Install the prepare-commit-msg hook.
  * Idempotent: re-running is safe.
  * Wraps existing non-git-mem hooks by renaming them to .user-backup.
+ * Upgrades outdated git-mem hooks in-place.
  */
 export function installHook(cwd?: string): IHookInstallResult {
   const gitDir = findGitDir(cwd || process.cwd());
@@ -98,11 +124,18 @@ export function installHook(cwd?: string): IHookInstallResult {
   const hookPath = join(hooksDir, 'prepare-commit-msg');
   const backupPath = join(hooksDir, 'prepare-commit-msg.user-backup');
 
-  // Already installed — idempotent
-  if (isGitMemHook(hookPath)) {
+  // Already installed and up-to-date — idempotent
+  if (isGitMemHook(hookPath) && isCurrentVersion(hookPath)) {
     return { installed: false, wrapped: false, hookPath };
   }
 
+  // Outdated git-mem hook — upgrade in-place
+  if (isGitMemHook(hookPath) && !isCurrentVersion(hookPath)) {
+    writeFileSync(hookPath, HOOK_SCRIPT);
+    chmodSync(hookPath, 0o755);
+    return { installed: true, wrapped: false, hookPath };
+  }
+
   let wrapped = false;
 
   // Existing non-git-mem hook — wrap it
diff --git a/src/mcp/tools/remember.ts b/src/mcp/tools/remember.ts
index cf8e200f..5a19ccf2 100644
--- a/src/mcp/tools/remember.ts
+++ b/src/mcp/tools/remember.ts
@@ -22,6 +22,8 @@ export function registerRememberTool(server: McpServer): void {
       confidence: z.enum(['verified', 'high', 'medium', 'low']).optional().describe('Confidence level (default: high)'),
       tags: z.string().optional().describe('Comma-separated tags'),
       lifecycle: z.enum(['permanent', 'project', 'session']).optional().describe('Lifecycle tier (default: project)'),
+      agent: z.string().optional().describe('AI agent name (default: auto-detect from $GIT_MEM_AGENT / $CLAUDE_CODE)'),
+      model: z.string().optional().describe('AI model identifier (default: $GIT_MEM_MODEL)'),
       trailers: z.boolean().optional().describe('Write AI-* trailers to commit message (default: true)'),
     },
     async (args) => {
@@ -30,6 +32,14 @@ export function registerRememberTool(server: McpServer): void {
       try {
         logger.info('Tool invoked', { type: args.type || 'fact' });
 
+        // Resolve agent: explicit param > $GIT_MEM_AGENT > $CLAUDE_CODE heuristic
+        const agent = args.agent
+          || process.env.GIT_MEM_AGENT
+          || (process.env.CLAUDE_CODE ? 'Claude-Code' : undefined);
+
+        // Resolve model: explicit param > $GIT_MEM_MODEL
+        const model = args.model || process.env.GIT_MEM_MODEL || undefined;
+
         const memory = memoryService.remember(args.text, {
           sha: args.commit,
           type: (args.type || 'fact') as MemoryType,
@@ -37,6 +47,8 @@ export function registerRememberTool(server: McpServer): void {
           lifecycle: (args.lifecycle || 'project') as MemoryLifecycle,
           tags: args.tags,
           trailers: args.trailers,
+          agent,
+          model,
         });
 
         return {
diff --git a/tests/unit/application/services/MemoryService.test.ts b/tests/unit/application/services/MemoryService.test.ts
index f76beff0..f8fda6f3 100644
--- a/tests/unit/application/services/MemoryService.test.ts
+++ b/tests/unit/application/services/MemoryService.test.ts
@@ -153,6 +153,38 @@ describe('MemoryService', () => {
       const trailers = trailerService.readTrailers('HEAD', repoDir);
       assert.ok(!trailers.find(t => t.key === 'AI-Tags'));
     });
+
+    it('should write AI-Agent and AI-Model trailers when provided', () => {
+      writeFileSync(join(repoDir, 'agent-model.txt'), 'agent-model');
+      git(['add', '.'], repoDir);
+      git(['commit', '-m', 'feat: agent model test'], repoDir);
+
+      serviceWithTrailers.remember('Memory with agent and model', {
+        cwd: repoDir,
+        type: 'fact',
+        agent: 'Claude-Code',
+        model: 'claude-opus-4-6',
+      });
+
+      const trailers = trailerService.readTrailers('HEAD', repoDir);
+      assert.ok(trailers.find(t => t.key === 'AI-Agent' && t.value === 'Claude-Code'));
+      assert.ok(trailers.find(t => t.key === 'AI-Model' && t.value === 'claude-opus-4-6'));
+    });
+
+    it('should not write AI-Agent or AI-Model trailers when not provided', () => {
+      writeFileSync(join(repoDir, 'no-agent-model.txt'), 'no-agent');
+      git(['add', '.'], repoDir);
+      git(['commit', '-m', 'feat: no agent model test'], repoDir);
+
+      serviceWithTrailers.remember('Memory without agent', {
+        cwd: repoDir,
+        type: 'fact',
+      });
+
+      const trailers = trailerService.readTrailers('HEAD', repoDir);
+      assert.ok(!trailers.find(t => t.key === 'AI-Agent'));
+      assert.ok(!trailers.find(t => t.key === 'AI-Model'));
+    });
   });
 
   describe('recall', () => {
diff --git a/tests/unit/hooks/prepare-commit-msg.test.ts b/tests/unit/hooks/prepare-commit-msg.test.ts
index 7bfcf820..ca9716bb 100644
--- a/tests/unit/hooks/prepare-commit-msg.test.ts
+++ b/tests/unit/hooks/prepare-commit-msg.test.ts
@@ -39,7 +39,7 @@ describe('installHook', () => {
 
     const content = readFileSync(result.hookPath, 'utf8');
     assert.ok(content.includes('#!/bin/sh'));
-    assert.ok(content.includes('git-mem:prepare-commit-msg v1'));
+    assert.ok(content.includes('git-mem:prepare-commit-msg v2'));
     assert.ok(content.includes('git interpret-trailers'));
     assert.ok(content.includes('AI-Agent'));
   });
@@ -75,12 +75,44 @@ describe('installHook', () => {
 
       // Installed hook should contain both fingerprint and wrapper reference
       const content = readFileSync(hookPath, 'utf8');
-      assert.ok(content.includes('git-mem:prepare-commit-msg v1'));
+      assert.ok(content.includes('git-mem:prepare-commit-msg v2'));
       assert.ok(content.includes('user-backup'));
     } finally {
       rmSync(freshRepo, { recursive: true, force: true });
     }
   });
+
+  it('should upgrade v1 hook to v2 on reinstall', () => {
+    const freshRepo = mkdtempSync(join(tmpdir(), 'git-mem-hook-upgrade-'));
+    git(['init'], freshRepo);
+
+    const hooksDir = join(freshRepo, '.git', 'hooks');
+    const hookPath = join(hooksDir, 'prepare-commit-msg');
+
+    // Write a v1 hook (old fingerprint, no AI-Model support)
+    const v1Hook = '#!/bin/sh\n# git-mem:prepare-commit-msg v1\n# Old hook without AI-Model\nexit 0\n';
+    mkdirSync(hooksDir, { recursive: true });
+    writeFileSync(hookPath, v1Hook);
+    chmodSync(hookPath, 0o755);
+
+    try {
+      const result = installHook(freshRepo);
+
+      // Should have upgraded in-place
+      assert.equal(result.installed, true);
+      assert.equal(result.wrapped, false);
+
+      const content = readFileSync(hookPath, 'utf8');
+      assert.ok(content.includes('git-mem:prepare-commit-msg v2'), 'Should be upgraded to v2');
+      assert.ok(content.includes('AI-Model'), 'Should include AI-Model support');
+
+      // Second install should be idempotent
+      const result2 = installHook(freshRepo);
+      assert.equal(result2.installed, false);
+    } finally {
+      rmSync(freshRepo, { recursive: true, force: true });
+    }
+  });
 });
 
 describe('uninstallHook', () => {
@@ -245,6 +277,52 @@ describe('hook integration — commit message modification', () => {
     assert.ok(message.includes('ExistingAgent'));
   });
 
+  it('should add AI-Model trailer when GIT_MEM_MODEL is set', () => {
+    writeFileSync(join(repoDir, 'model-test.txt'), 'model');
+    git(['add', '.'], repoDir);
+
+    execFileSync('git', ['commit', '-m', 'feat: model trailer test'], {
+      encoding: 'utf8',
+      cwd: repoDir,
+      env: { ...process.env, GIT_MEM_AGENT: 'TestAgent', GIT_MEM_MODEL: 'claude-opus-4-6' },
+    });
+
+    const message = git(['log', '-1', '--format=%B'], repoDir);
+    assert.ok(message.includes('AI-Model: claude-opus-4-6'), `Expected AI-Model trailer in: ${message}`);
+  });
+
+  it('should not add AI-Model trailer when GIT_MEM_MODEL is not set', () => {
+    writeFileSync(join(repoDir, 'no-model.txt'), 'no-model');
+    git(['add', '.'], repoDir);
+
+    const cleanEnv = { ...process.env, GIT_MEM_AGENT: 'TestAgent' };
+    delete cleanEnv.GIT_MEM_MODEL;
+
+    execFileSync('git', ['commit', '-m', 'feat: no model test'], {
+      encoding: 'utf8',
+      cwd: repoDir,
+      env: cleanEnv,
+    });
+
+    const message = git(['log', '-1', '--format=%B'], repoDir);
+    assert.ok(!message.includes('AI-Model:'), `Should not have AI-Model trailer in: ${message}`);
+  });
+
+  it('should add both AI-Agent and AI-Model when both env vars set', () => {
+    writeFileSync(join(repoDir, 'both-trailers.txt'), 'both');
+    git(['add', '.'], repoDir);
+
+    execFileSync('git', ['commit', '-m', 'feat: both trailers test'], {
+      encoding: 'utf8',
+      cwd: repoDir,
+      env: { ...process.env, GIT_MEM_AGENT: 'Claude-Code', GIT_MEM_MODEL: 'claude-opus-4-6' },
+    });
+
+    const message = git(['log', '-1', '--format=%B'], repoDir);
+    assert.ok(message.includes('AI-Agent: Claude-Code'), `Expected AI-Agent trailer in: ${message}`);
+    assert.ok(message.includes('AI-Model: claude-opus-4-6'), `Expected AI-Model trailer in: ${message}`);
+  });
+
   it('should skip merge commits', () => {
     // Determine the default branch name before creating feature branch
     const defaultBranch = git(['rev-parse', '--abbrev-ref', 'HEAD'], repoDir);