diff --git a/src/app/new/form-reducer.test.ts b/src/app/new/form-reducer.test.ts
index 1b2949f9..d5ac6ed3 100644
--- a/src/app/new/form-reducer.test.ts
+++ b/src/app/new/form-reducer.test.ts
@@ -1,5 +1,6 @@
 import { describe, it, expect } from 'vitest';
 import { formReducer, initialFormState } from './form-reducer';
+import { SESSION_NAME_MAX_LENGTH } from '@/lib/types';
 import type { FormState } from './form-reducer';
 import type { Repo } from '@/components/RepoSelector';
 import type { Issue } from '@/lib/types';
@@ -204,6 +205,25 @@ describe('formReducer', () => {
       expect(result.initialPrompt).toBe('');
     });
 
+    it('truncates session name to max length when issue title is very long', () => {
+      const longTitle = 'A'.repeat(200);
+      const longIssue: Issue = {
+        ...mockIssue,
+        number: 1,
+        title: longTitle,
+      };
+      const state: FormState = {
+        ...initialFormState,
+        selectedRepo: mockRepo,
+        selectedBranch: 'main',
+      };
+
+      const result = formReducer(state, { type: 'selectIssue', issue: longIssue });
+
+      expect(result.sessionName.length).toBe(SESSION_NAME_MAX_LENGTH);
+      expect(result.sessionName).toBe(`#1: ${longTitle}`.slice(0, SESSION_NAME_MAX_LENGTH));
+    });
+
     it('preserves session name when issue is deselected and name was manually edited', () => {
       const state: FormState = {
         ...initialFormState,
diff --git a/src/app/new/form-reducer.ts b/src/app/new/form-reducer.ts
index a089b76a..cc19df07 100644
--- a/src/app/new/form-reducer.ts
+++ b/src/app/new/form-reducer.ts
@@ -1,5 +1,5 @@
 import type { Repo } from '@/components/RepoSelector';
-import type { Issue } from '@/lib/types';
+import { SESSION_NAME_MAX_LENGTH, type Issue } from '@/lib/types';
 
 export interface FormState {
   selectedRepo: Repo | null;
@@ -44,7 +44,7 @@ export function formReducer(state: FormState, action: FormAction): FormState {
         sessionName: state.nameManuallyEdited
           ? state.sessionName
           : action.issue
-            ? `#${action.issue.number}: ${action.issue.title}`
+            ? `#${action.issue.number}: ${action.issue.title}`.slice(0, SESSION_NAME_MAX_LENGTH)
             : '',
         initialPrompt: state.promptManuallyEdited
           ? state.initialPrompt
diff --git a/src/app/new/page.tsx b/src/app/new/page.tsx
index c0f8eaf7..0b22ab3b 100644
--- a/src/app/new/page.tsx
+++ b/src/app/new/page.tsx
@@ -18,6 +18,7 @@ import { BranchSelector } from '@/components/BranchSelector';
 import { IssueSelector } from '@/components/IssueSelector';
 import type { Repo } from '@/components/RepoSelector';
 import type { Issue } from '@/lib/types';
+import { SESSION_NAME_MAX_LENGTH } from '@/lib/types';
 import { formReducer, initialFormState } from './form-reducer';
 
 function generateIssuePrompt(issue: Issue, repoFullName: string): string {
@@ -115,9 +116,9 @@ function NewSessionForm() {
       return;
     }
 
-    const defaultName = isNoRepo
-      ? 'Workspace'
-      : `${form.selectedRepo.name} - ${form.selectedBranch}`;
+    const defaultName = (
+      isNoRepo ? 'Workspace' : `${form.selectedRepo.name} - ${form.selectedBranch}`
+    ).slice(0, SESSION_NAME_MAX_LENGTH);
 
     createMutation.mutate({
       name: form.sessionName || defaultName,
@@ -164,6 +165,7 @@ function NewSessionForm() {
               type="text"
               value={form.sessionName}
               onChange={handleNameChange}
+              maxLength={SESSION_NAME_MAX_LENGTH}
               placeholder={
                 isNoRepo
                   ? 'Workspace'
diff --git a/src/lib/types.ts b/src/lib/types.ts
index 754c5b97..44e373db 100644
--- a/src/lib/types.ts
+++ b/src/lib/types.ts
@@ -19,6 +19,9 @@ export const MessageType = {
 
 export type MessageType = (typeof MessageType)[keyof typeof MessageType];
 
+// Session constants
+export const SESSION_NAME_MAX_LENGTH = 100;
+
 // Session interface
 export interface Session {
   id: string;
diff --git a/src/server/routers/sessions.ts b/src/server/routers/sessions.ts
index d20abfb3..4fcaa6f1 100644
--- a/src/server/routers/sessions.ts
+++ b/src/server/routers/sessions.ts
@@ -13,6 +13,7 @@ import { runClaudeCommand, stopSession } from '../services/claude-runner';
 import { sseEvents } from '../services/events';
 import { createLogger, toError } from '@/lib/logger';
 import { env } from '@/lib/env';
+import { SESSION_NAME_MAX_LENGTH } from '@/lib/types';
 
 const log = createLogger('sessions');
 
@@ -111,7 +112,7 @@ export const sessionsRouter = router({
   create: protectedProcedure
     .input(
       z.object({
-        name: z.string().min(1).max(100),
+        name: z.string().min(1).max(SESSION_NAME_MAX_LENGTH),
         repoFullName: z
           .string()
           .regex(/^[\w-]+\/[\w.-]+$/)