[DOCS] Fullscreen `fullscreen.md` tmux caveat still says synchronized output is unsupported; v2.1.200 enabled it for tmux 3.4+

Documentation Type

Incorrect/outdated documentation

Documentation Location

https://code.claude.com/docs/en/fullscreen

Section/Topic

The "Use with tmux" section of fullscreen.md (the third caveat in the tmux list) and the matching CLAUDE_CODE_FORCE_SYNC_OUTPUT row in env-vars.md.

Current Documentation

fullscreen.md:155 currently reads:

tmux doesn't support synchronized output, so you may see more flicker during redraws than when running Claude Code directly in your terminal. If the flicker is noticeable, especially over SSH, run Claude Code in its own terminal tab outside tmux.

env-vars.md:215 documents CLAUDE_CODE_FORCE_SYNC_OUTPUT as:

Set to 1 to force-enable DEC private mode 2026 synchronized output when your terminal supports it but is not auto-detected. Useful for emulators such as Emacs eat that implement BSU/ESU but do not reply to the capability probe. Has no effect under tmux

What's Wrong or Missing?

A. The "tmux doesn't support synchronized output" claim is no longer true in tmux 3.4+

The v2.1.200 changelog says:

Fixed rendering flicker under tmux 3.4+ by enabling synchronized terminal output

tmux 3.4 added synchronized output support, and Claude Code v2.1.200 turns it on automatically when it detects tmux 3.4 or newer. The fullscreen.md caveat still says tmux never supports synchronized output, which is incorrect for the supported version range.

B. The CLAUDE_CODE_FORCE_SYNC_OUTPUT row claims "Has no effect under tmux"

The variable's description was written for the era when tmux had no synchronized-output support and the variable was therefore irrelevant inside tmux. After v2.1.200 the auto-enable path handles tmux 3.4+, so the variable's "Has no effect under tmux" note is misleading: it now affects tmux sessions only when auto-detection disagrees with the user.

C. The recommendation "run Claude Code in its own terminal tab outside tmux" is no longer necessary

The current prose ends by suggesting the user drop tmux to avoid flicker. With v2.1.200 this workaround is unnecessary on tmux 3.4+, and the user reading the page will waste time chasing a workaround the docs describe as their only option.

Suggested Improvement

Update fullscreen.md:155 to reflect the v2.1.200 behavior, for example:

{/ min-version: 2.1.200 /}Claude Code enables DEC private mode 2026 synchronized output automatically under tmux 3.4 and later, which removes the redraw flicker that older tmux versions produced. On tmux 3.3 and earlier the same flicker is still expected, and running Claude Code in its own terminal tab outside tmux remains the workaround.

Update the CLAUDE_CODE_FORCE_SYNC_OUTPUT row in env-vars.md to drop the "Has no effect under tmux" sentence and note that under tmux 3.4+ the variable is honored when auto-detection is overridden.

Impact

Medium - Makes feature difficult to understand

Additional Context

Affected Pages:
| Page | Line(s) | Context |
|------|---------|---------|
| https://code.claude.com/docs/en/fullscreen | 155 | "Use with tmux" caveat |
| https://code.claude.com/docs/en/env-vars | 215 | CLAUDE_CODE_FORCE_SYNC_OUTPUT row |

Total scope: 2 pages, one prose paragraph and one environment variable row.

The release note for this fix appears in v2.1.200 (July 3, 2026).