diff --git a/packages/app/e2e/regression/session-timeline-lifecycle-state.spec.ts b/packages/app/e2e/regression/session-timeline-lifecycle-state.spec.ts
index d9c85997cf2..f81dd081adc 100644
--- a/packages/app/e2e/regression/session-timeline-lifecycle-state.spec.ts
+++ b/packages/app/e2e/regression/session-timeline-lifecycle-state.spec.ts
@@ -59,12 +59,12 @@ test("transitions a streaming shell from writing through command execution", asy
   await expect(tool.locator('[data-slot="collapsible-trigger"]')).toHaveCSS("height", "28px")
   await expect(tool.locator('[data-component="tool-trigger"]')).toHaveCSS("gap", "6px")
   await expect(title).toHaveCSS("font-size", "13px")
-  await expect(title).toHaveCSS("font-family", "Inter, sans-serif")
+  await expect(title).toHaveCSS("font-family", /^Inter,/)
   await expect(title).toHaveCSS("font-weight", "530")
   await expect(title).toHaveCSS("line-height", "16px")
   await expect(title).toHaveCSS("color", "rgb(22, 22, 22)")
   await expect(subtitle).toHaveCSS("font-size", "13px")
-  await expect(subtitle).toHaveCSS("font-family", "Inter, sans-serif")
+  await expect(subtitle).toHaveCSS("font-family", /^Inter,/)
   await expect(subtitle).toHaveCSS("font-weight", "440")
   await expect(subtitle).toHaveCSS("line-height", "16px")
   await expect(subtitle).toHaveCSS("color", "rgb(92, 92, 92)")
diff --git a/packages/app/src/settings/model.test.ts b/packages/app/src/settings/model.test.ts
new file mode 100644
index 00000000000..36612ac9963
--- /dev/null
+++ b/packages/app/src/settings/model.test.ts
@@ -0,0 +1,30 @@
+import { describe, expect, test } from "bun:test"
+import { monoDefault, monoFontFamily, sansDefault, sansFontFamily, terminalFontFamily } from "./model"
+
+describe("settings font families", () => {
+  test("defaults normal text to Inter", () => {
+    expect(sansDefault).toBe("Inter")
+    expect(sansFontFamily(undefined)).toStartWith('"Inter", ')
+    expect(sansFontFamily("")).toStartWith('"Inter", ')
+    expect(sansFontFamily("   ")).toStartWith('"Inter", ')
+  })
+
+  test("keeps custom normal fonts ahead of the default", () => {
+    expect(sansFontFamily("Custom Sans")).toStartWith('"Custom Sans", "Inter", ')
+  })
+
+  test("defaults monospace text to IBM Plex Mono", () => {
+    expect(monoDefault).toBe("IBM Plex Mono")
+    expect(monoFontFamily(undefined)).toStartWith('"IBM Plex Mono", ')
+    expect(monoFontFamily("")).toStartWith('"IBM Plex Mono", ')
+    expect(monoFontFamily("   ")).toStartWith('"IBM Plex Mono", ')
+  })
+
+  test("keeps custom monospace fonts ahead of the default", () => {
+    expect(monoFontFamily("Custom Mono")).toStartWith('"Custom Mono", "IBM Plex Mono", ')
+  })
+
+  test("preserves the separate terminal font default", () => {
+    expect(terminalFontFamily(undefined)).toStartWith('"JetBrainsMono Nerd Font Mono", ')
+  })
+})
diff --git a/packages/app/src/settings/model.tsx b/packages/app/src/settings/model.tsx
index 614bc5df7ef..f64e99abe69 100644
--- a/packages/app/src/settings/model.tsx
+++ b/packages/app/src/settings/model.tsx
@@ -60,12 +60,12 @@ export interface Settings {
   sounds: SoundSettings
 }
 
-export const monoDefault = "System Mono"
-export const sansDefault = "System Sans"
+export const monoDefault = "IBM Plex Mono"
+export const sansDefault = "Inter"
 export const terminalDefault = "JetBrainsMono Nerd Font Mono"
 const monoFallback =
-  'ui-monospace, SFMono-Regular, Menlo, Monaco, Consolas, "Liberation Mono", "Courier New", monospace'
-const sansFallback = 'ui-sans-serif, system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif'
+  '"IBM Plex Mono", ui-monospace, SFMono-Regular, Menlo, Monaco, Consolas, "Liberation Mono", "Courier New", monospace'
+const sansFallback = '"Inter", ui-sans-serif, system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif'
 const terminalFallback =
   '"JetBrainsMono Nerd Font Mono", ui-monospace, SFMono-Regular, Menlo, Monaco, Consolas, "Liberation Mono", "Courier New", monospace'
 
diff --git a/packages/ui/src/styles/theme.css b/packages/ui/src/styles/theme.css
index b652f9610d3..f37f41b9682 100644
--- a/packages/ui/src/styles/theme.css
+++ b/packages/ui/src/styles/theme.css
@@ -1,8 +1,8 @@
 :root {
-  --font-family-sans: ui-sans-serif, system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif;
+  --font-family-sans: "Inter", ui-sans-serif, system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif;
   --font-family-sans--font-feature-settings: normal;
   --font-family-mono:
-    ui-monospace, SFMono-Regular, Menlo, Monaco, Consolas, "Liberation Mono", "Courier New", monospace;
+    "IBM Plex Mono", ui-monospace, SFMono-Regular, Menlo, Monaco, Consolas, "Liberation Mono", "Courier New", monospace;
   --font-family-mono--font-feature-settings: normal;
 
   --font-size-small: 13px;
diff --git a/packages/ui/src/styles/tokens/theme.css b/packages/ui/src/styles/tokens/theme.css
index ba414282346..41593dfff32 100644
--- a/packages/ui/src/styles/tokens/theme.css
+++ b/packages/ui/src/styles/tokens/theme.css
@@ -129,9 +129,9 @@
     --v2-illustration-illustration-layer-02: var(--v2-grey-400);
     --v2-illustration-illustration-layer-03: var(--v2-grey-500);
 
-    --font-family-text: "Inter", sans-serif;
-    --v2-font-family-sans: "Inter", sans-serif;
-    --v2-font-family-code: "IBM Plex Mono", var(--font-family-mono);
+    --font-family-text: var(--font-family-sans);
+    --v2-font-family-sans: var(--font-family-sans);
+    --v2-font-family-code: var(--font-family-mono);
     --line-height-tight: 12px;
     --line-height-compact: 16px;
     --line-height-base: 20px;